home > Water supply > What options exist for database classification? According to the nature of the information stored. Classification of databases based on the type of stored data

What options exist for database classification? According to the nature of the information stored. Classification of databases based on the type of stored data

Database

For example:

Factual

takh presented in strictly a certain format.

Documentary

)

Information storage input procedure

search – request processing process;

treatment

issuance of information

Centralized database –

According to the organizational structure, databases are divided into

Relational databases data are called databases with a tabular form of organization.

In relational databases, a table row is called a record, and a column is called a field. In general it looks like this:

The main key in databases is a field (or a set of fields) whose value is not repeated in different records.

BASIC DATA TYPES

text	one line of text (up to 255 characters)
MEMO field	text consisting of several lines that can be
	view using scroll bars (up to 65535 characters)
numerical	number of any type (can be used in calculations)
monetary	field expressed in monetary units (rubles, dollars, etc.)
date Time	a field containing a date or time
counter	field that is entered automatically with each entry
logical	contains one of the values True (true) or False (false) and is used in logical operations

OLE object field	contains pictures, audio files, Excel spreadsheets, Word document, etc.

Database

Database- database and its management system (DBMS). A DBMS (for example, FoxPro) is an application for creating databases as a collection of two-dimensional tables.

Data Bank (BnD)	is a system of specially organized data, software, language, organizational and technical tools designed for centralized accumulation and collective multi-purpose use of data.
Databases (DB)	is a named collection of data that reflects the state of objects and their relationships in the subject area under consideration. A characteristic feature of databases is persistence: data is constantly accumulated and used; the composition and structure of data, necessary for solving certain applied problems, are usually constant and stable over time; individual or even all data elements may change - but these are also manifestations of constancy - constant relevance.
Database management system (DBMS)	is a set of language and software tools designed for creating, maintaining and sharing a database with many users.

2.The concept of a database, DBMS, IP . Examples of use and scope of databases

Database(DB) is structured knowledge about objects.

A database helps organize and store information from a specific subject area, makes it easier to access data, search and provide the necessary information. The simplest database can be considered a telephone directory or a list of books in your home library. Modern databases operate with information presented in a variety of formats, from ordinary numbers and text to graphic and video data.

Database- a set of information stored in some ordered way. You can compare a database to a cabinet in which documents are stored. In other words, a database is a data store. Databases themselves would not be of interest if there were no database management systems (DBMS).

Database Management System is a set of language and software tools that provides access to data, allows them to be created, changed and deleted, ensures data security, etc. In general, a DBMS is a system that allows you to create databases and manipulate information from them. And it provides this access to DBMS data through a special language - SQL.

SQL is a structured query language whose main purpose is to provide a simple way to read and write information to a database.

So, the simplest scheme for working with a database looks something like this:

The main purpose of the database is “permanent use”. Speaking about the use of databases, it is necessary to mention the concept Information system(IS).

IP is a complex of software, hardware, organizational and other tools that provide data processing.

The core, the “heart” of the IS is precisely the database. Of course, information systems can be quite complex, including those built on several databases, but this does not change the essence - a database, in principle, can be imagined as something autonomous, but it is impossible to imagine an information system that is not based on a database.

Database structure

When creating a database, we strive to organize information according to various criteria in order to then extract from it the data we need in any combination. This can only be done if the data is structured. Structuring is a set of conventions about ways to present data. It is clear that information can be structured in different ways. Depending on the structure, there are hierarchical, network, relational, object-oriented and hybrid database models.

It is customary to distinguish the following types of databases: hierarchical, network, relational And object-oriented.

Keys

Table keyis a field or group of fields containing unique values within a given table. The key uniquely identifies the corresponding table row. If the key consists of a single field, it is often called simple, if from several - composite.

7. Types of relationships between tables in the relational database model

Communication allows you to model relationships between domain objects. The connection name must be unique throughout the model.

There are 4 types of connections:

1. "One to one"- any instance of entity A corresponds to only one instance of entity B, and vice versa.

Any given student can only have one characteristic, and that characteristic applies to a single student.

2. "One-to-many"- any instance of entity A corresponds to 0, 1 or several instances of entity B, but any instance of entity B corresponds to only one instance of entity A.

The student is given many grades; The assigned grade belongs to only one student.

3. "Many-to-one"- any instance of entity A corresponds to only one instance of entity B, but any instance of entity B corresponds to 0, 1 or several instances of entity A.

A teacher works in only one office, but an office can be assigned to several teachers.

What's the difference between one-to-many and many-to-one relationships? The same as between the phrases “student’s briefcase” and “student’s briefcase.” That is, it is important who is in charge in the relationship between two objects - the student or the portfolio. The essence of the relationship between two objects is reflected in the name of the relationship.

If, when defining a connection, it is difficult for you to identify subordination, then there is only one conclusion: you have a poor understanding of the subject area.

4. "Many-to-many"- any instance of entity A corresponds to 0, 1 or several instances of entity B, and any instance of entity B corresponds to 0, 1 or several instances of entity A.

Student Ivanov studies with several teachers. And each teacher works with many students.

Normalization of relations

The results of information modeling can be summarized in a single table. But it is impossible to use it, because... Most likely, these tables will contain redundant, repeating information.
Therefore, the obtained data is subjected to transformations called normalization.

First normal form

The relationship is called reduced to first normal form, if all its attributes are simple.

First normal form dictates that all data contained in a table must be atomic(indivisible).

The rule means that each field of each record must contain only one value, and not an array or any other data structure.

Since the value of the Ratings field is not atomic, the table does not meet the requirements of 1NF.

Second normal form

The relation is in second normal form, if it is in first normal form and the values in each non-key attribute are uniquely determined by the value of the primary key.

In other words, the value of each field must be determined entirely by the value of the primary key. It is important to note that dependence on a primary key is understood precisely as a dependence on the key as a whole, and not on its individual component (in the case of a composite key).

Let's give an example of a table that is not in 2NF.

As we remember, this table has a composite key Date+Time of day. The Temperature field is completely dependent on the primary key - there are no problems with it. But the Sunrise field depends only on the Date field. The time of day does not naturally affect the time of sunrise.

Here it is appropriate to ask the question: what is the practical meaning of 2NF? What is the use of these restrictions? It turns out it's big. Let's say that in the above example the developer ignores the 2NF requirements. Firstly, most likely there will be a so-called redundancy- storage of unnecessary data. After all, if for one record with a given date the sunrise time is already stored, then for all other records with a given date it should be the same and, generally speaking, there is no need to store it.

Third normal form

The relation is in third normal form, if it is in second normal form and all non-key attributes are independent of each other.

The mutual dependence of the columns is conveniently understood as follows: Columns are mutually dependent if it is impossible to change one of them without changing the other.

Let's give an example of a table that is not in 3NF. Let's consider an example of a simple notebook for storing home telephone numbers of people living, perhaps, in different regions of the country.

This table has a dependency between the non-key columns City and City Code, therefore the table is not in 3NF.

Fourth normal form

The relation is in fourth normal form, if it is in third normal form and if it does not contain independent groups of attributes between which there is a many-to-many relationship.

In the theory of relational databases, higher order forms are also considered - Boyce-Codd normal form, 4NF, 5NF and even higher. These forms do not have much practical significance, and developers, as a rule, always stop at 3NF.

Indexing

Indexing is extremely important from the point of view of practical application.

The main purpose of indexing is to optimize (speed up) search (and, accordingly, some other operations with the database).

Indexing in any case requires additional resources (special index files are most often created at the physical level). Indexing may even slow down operations related to data modification; therefore, tables that are rarely modified and frequently searched are usually indexed.

An index file is very similar to a regular book index. For each index value, a list of table rows that contain that value is stored. Accordingly, to search, you do not need to look through the entire table - just look into the index. However, when modifying records, you may need to rebuild the index. And this takes extra time.

Data types

When they talk about the properties of an entity (object), they explicitly or implicitly mean that each specific property (in a table - a record field) takes values from a certain set. This set is called data type.

All relational DBMSs support data of the following main types:

· numeric;

· strings;

· brain teaser;

The above list is not exhaustive. As a rule, DBMSs also have types for storing large text and binary data, special “monetary” types, etc. The following figure, a screenshot of the Microsoft Access Table Designer, shows the types supported by this system.

Note also that, as a rule, types can be equipped with modifiers that clarify the corresponding set of data (range of values). For example, in Microsoft Access, numeric data type can simply be “integer”, “long integer”, “real”, etc. - see picture.

11.Codd Rules (requirements for relational databases)

Most DBMSs distributed on PCs are considered to be relational, although they are not fully so. In addition to presenting data in the form of two-dimensional tables, belonging to the category of relational systems is determined by a number of characteristics formulated by Codd, called Codd's rules.

Let's list these rules:

1) Explicit presentation of data.

All data must be presented explicitly and their values must be calculated by indirect algorithms (with the exception of single-valued mappings).

Example: if gender is not explicitly specified, then it cannot be (erroneously) obtained from the surname, because Different algorithms for interpreting a surname in different applications can cause inconsistencies (violate integrity) in the database. For explicit representation, types are needed: numbers, strings, dates, times, etc.

2) Guaranteed access to data.

All information in the database must be accessible to the application. Selection of any value in the RDB is performed when specifying:

a) the name of the relationship;

b) a pointer to a tuple (for example, the value of the primary key of the tuple);

c) attribute name;

(relation_name, primary key, attribute)

3) Complete handling of undefined values.

Null values other than any defined value must be supported for all data types in all operations.

4) Access to the database in terms of the relational model.

The description of the database (list of relationships, definitions of relationship schemes and keys, statistical information, etc.) must be written in a relational language. The user must be able to access this information using a relational language. Those. It should be possible to administer databases independently of applications.

5) Completeness of a subset of a relational language.

A relational schema can support multiple languages, at least DDL and DML. However, at least one of the languages must have a sentence syntax that supports the following concepts:

Data definition (relationships, attributes, domains, keys, integrity constraints);

Definition of virtual (imaginary) relations formed using relational expressions based on one or more relations (definition of representations);

Data manipulation (interactive or programmatic);

Integrity constraint;

Authorized access;

Transaction management (starting a transaction, committing execution, abandoning execution).

6) Updateability of views.

All views (virtual relations) should be automatically updated when data in the underlying relations is modified. If, for example, A = R È S, and A is a representation, then A must be updated as soon as R or S changes.

7) Availability of a high-level data manipulation language.

The insert, update, and delete operations must be applied to the relation as a whole:

providing control over the integrity of the database when modifying relationships. When performing an insert on a relation as a whole, it is easy to check the uniqueness of the primary key, restrictions on values, etc.

8) Physical independence of data.

Application programs should not depend on the methods used for storing data on storage media and methods of accessing them.

Physically independent ensures the functionality of applications when the location of data on the network changes.

9) Logical data independence.

Application programs should not depend on the implementation of any of the views (virtual relations) used.

By defining virtual relations within the database, you can develop applications that use this relation without worrying that the database structure will change and the virtual relations will be built on the basis of a different relational expression.

10) Independence of integrity control.

All integrity constraints and external representations (virtual relationships, reports) should not be defined in applications, but should be defined using a data definition language and stored in a database directory (dictionary).

11) Distributive independence.

A relational system must be distributable and portable. Creating heterogeneous computer systems requires providing access to databases in different OS and on different platforms.

Distribution independence involves the full implementation of a DBMS for various platforms or the implementation of communication blocks as part of a DBMS, allowing data exchange between different DBMSs.

12) Coordination of language levels.

If the relational system has a low-level access language (access element - record) and a high-level access language (access element - relationships). The execution of low-level commands must be carried out with integrity control, just as with high-level commands.

12.Formalization of the datalogical model in the language of a specific DBMS (using the example of Access)

After the structure of the database has been determined, it is necessary to formalize the datalogical model in the language of a specific DBMS, in other words - describe the tables. Most modern DBMSs provide convenient visual designers for this purpose (for example, we have already mentioned the Microsoft Access table designer above). The description (construction) of each table includes:

· Determining the table name. If the table is a representation of some entity, then the name usually corresponds to the name of the entity. The names of link tables are usually formed from the names of the entities being linked.

· Define field names and types. At the same stage, it is usually necessary to set the specific properties of specific fields - whether the field can contain “empty” (undefined) values, what the “default” value should be, etc.

· Defining a primary key. Although the relational model requires each table to have a primary key, most DBMSs allow you to not define a key in a table. This, of course, should be avoided. To the credit of the DBMS, they almost always try to “guide the developer on the right path” (see, for example, the figure).

· Defining (if necessary) indexed fields.

After constructing the tables, you need to install communications between them. Microsoft Access has a special tool for this - “Data Schema”. It is very convenient to “draw” connections between tables on the diagram by dragging and overlaying related fields on top of each other. In most cases, Access is able to determine the type of connection being made. For example, if the primary key of one table is linked to a non-primary key field in another, it is easy to understand—and Access understands—that this is a one-to-many relationship.

Other DBMSs have similar functions and interfaces to visual design tools.

Whatever visual interface a particular DBMS provides to developers, in the vast majority of cases, behind the scenes there is a common SQL language for all relational DBMSs ( S structuredQ ueryL anguage).

It is clear that this possibility can be provided only if there is some common system-independent kernel, which is SQL.)

13.Database objects . Tables, reports, pages, macros and modules. Requests and Forms.

Tables– the main objects of any database, which store all the data in the database and the structure of the database itself (fields, their types and properties).

Reports– are intended for data output, and for output not to the screen, but to a printing device (printer). They take special measures to group the output data and to display special design elements characteristic of printed documents (header and footer, page numbers, time of report creation, etc.).

Pages or data access pages - special database objects executed in HTML code, placed on a web page and transmitted to the client along with it. The object itself is not a database; a visitor can use it to view database records in the fields of the access page. Thus, pages are the interface between the client, server and database hosted on the server.

Macros and modules– designed to automate repetitive operations when working with the database management system, as well as to create new functions through programming. Macros consist of a sequence of internal DBMS commands and are one of the means of automating work with the database. Modules are created using an external programming language. This is one of the means by which a database developer can add non-standard functionality to it, satisfy specific customer requirements, increase the performance of the control system, and its level of security.

Requests and Forms.

Requests– serve to extract data from tables and present them to the user in a convenient form. With their help, data is selected, sorted and filtered. You can convert data using a given algorithm, create new tables, automatically populate tables with data imported from other sources, perform simple calculations in tables, and much more.

The peculiarity of queries is that they draw data from base tables and create temporary data based on them. resulting table(snapshot) – an image of fields and records selected from the base tables. Working with an image is faster and more efficient than working with tables stored on the hard drive.

The database can also be updated using a query. All data is entered into the base tables in the order they are received, i.e. they are not ordered. But with the appropriate request, you can get data sorted and filtered as needed.

Forms– data entry tools that provide the user with the fields necessary to fill out. You can place special controls in them (counters, drop-down lists, switches, checkboxes, etc.) to automate input. Example, filling out certain fields of the form. When displaying data using forms, you can use special means for their design.

14.SQL language (structured query language) .History of occurrence. Subsets of the language.

From SQL history:

All relational DBMSs support a special SQL language ( S texturedQ uery L anguage) on which requests are recorded. In fact, SQL consists of two languages - DML ( D ataM anipulationL anguage) and DDL ( D ataD eclarationL anguage).

The history of the SQL language began in 1974. The first prototype of the language was called SEQUEL (the name is derived from S structuredE nglishQue ryL anguage). Subsequently, the revised version of SEQUEL was called SQL. The first language standard was adopted in 1987.

SQL is a declarative language. This means that the client only specifies What exactly what he needs, and How it is decided by the DBMS itself to obtain this.

It must be said that although SQL was intended to be an end-user tool, it eventually became so complex that it became a programmer's tool. SQL defines two subsets of the language:

SQL-DDL(Data Definition Language) - a language for defining structures and integrity constraints of databases. These include commands for creating and deleting databases; creating, modifying and deleting tables; user management, etc.
SQL-DML(Data Manipulation Language) - data manipulation language: adding, changing, deleting and retrieving data, transaction management

Database. Types of databases by the nature of the information stored, by the method of storage, by the structure of the organization. Basic data types.

Database- an organized collection of data intended for long-term storage in external computer memory and permanent use

For example:

Library book collection database;

Database of the institution's personnel;

Database of legislative acts in the field of criminal law;

Database of modern pop songs.

Factual

Factual databases contain brief information about the objects being described.

takh presented in strictly a certain format.

For example, the library database stores bibliographic information about each book.

Documentary

Documentary databases contain documents (information) of various types: text, graphic, audio, multimedia

(for example, various reference books, dictionaries )

An information system is a combination of a database and the entire complex of hardware and software for storing, changing and retrieving information for interaction with the user.

Information storage – railway station database; input procedure – entering the client’s passport data;

search – request processing process;

treatment – the client’s choice of the date and time of train departure;

issuance of information – your order has been accepted, the ticket is booked

Centralized database –

The database is stored on one computer

Distributed database – different parts of one database are stored on multiple

a number of computers interconnected by a network

DBS are complex systems, and their classification can be made both for the entire DBS and for each component separately (Fig. 9). The central component of the SDB is the database and most of the classification criteria relate to it.

According to the form of information presentation distinguish between visual, audio and multimedia systems. This classification shows the form in which information is stored in the database and provided to users.

By the nature of data organization Databases can be divided into unstructured, semi-structured and structured.

To unstructured databases organized in the form of semantic networks can be included.

Partially structured can be considered a plain text database or a hypertext system.

Structured databases require preliminary design and description of the structure.

Structured databases by type of model used are divided into

· hierarchical,

· network,

· relational,

· mixed and

· multi model.

This classification also applies to DBMS.

In structured databases there are several levels information units (IE) , included in one another.

Most systems support:

· field – the smallest semantic unit of information;

· a set of fields (or more complex IUs) forms record b;

· a set of records of the same type represents database file .

Many DBMSs explicitly support the database level as a collection of interconnected database files.

By type of information stored DBs are divided into

· factual,

· documentary and

· lexicographic.

In factual databases information of a factual nature is stored - numerical or textual characteristics of objects, presented in a formalized form. In response to a request, information about the object of interest is provided.

In documentary databases the storage unit is a document and the user is given a link to the document or the document itself. Documentary databases are organized without storage and with storage of the document on computer media. The first type includes bibliographic, abstract and database indexes , referring to the source of information. Systems that store the full text of a document are called full text . Their variety is DB of document forms, in which a document is searched for use as a template.

To lexicographic databases include various dictionaries (classifiers, multilingual dictionaries, dictionaries of basic words, etc.).

By the nature of the organization of data storage and access to it differentiate

· local (personal),

· general (integrated,

· centralized) and

· distributed databases (Fig. 10).

Rice. 10. Classification of databases according to the nature of data storage and access

Personal database intended for local use by one user. Local databases can be created by each user independently, or can be retrieved from a common database.

Integrated and distributed databases suggest the possibility of simultaneous access to information by several users (multi-user access mode). Parts of distributed databases are physically located on different computers, but logically represent a single whole.

Other components of the database can also be distributed among network nodes. The database itself may be undistributed. Therefore they distinguish:

· distributed databases;

· distributed databases(in which at least one component is distributed).

Some sources mention extensional and intensional DB. The first ones are built using explicit storage of data in the database, the second ones are built using rules that determine their content.

Databases are also classified by volume . A special place here is occupied by the so-called very large databases . For large databases, the issues of ensuring the efficiency of storing information and ensuring its processing are posed differently.

DBMS classification

By language of communication DBMS are divided into

· open,

· closed and

· mixed.

In open systems, universal languages are used to access databases. Closed systems have their own languages of communication with DBS users.

According to the DBMS functions performed are divided into

· informational and

· operating rooms.

Information systems allow you to organize information storage and access to it. For more complex processing, special programs are required. Operating rooms perform complex processing and can change processing algorithms.

By scope of possible application differentiate

· universal and

· specialized (problem-oriented DBMS).

The set of data types in different DBMSs is different. A number of DBMSs allow the developer to add new data types and new operations. Such systems are called extensible database systems . Further developments are object-oriented database systems, with powerful modeling capabilities for complex objects.

By DBMS power are divided into

· desktop (Dbase, FoxBase/FoxPro, Clipper, Paradox, Access, Approach) and

· corporate (Oracle, DB2, Sybase, Informix, Ingres, Progress).

For the first characterized by low requirements for technical means, focus on the end user and low cost.

Second provide work in a distributed environment, high performance, have developed administration tools, and ample capabilities for maintaining integrity. They are complex, expensive and require significant resources.

Among the DBMSs occupying an intermediate position between desktop and industrial systems, one can name Interbase, Microsoft SQL Server. In recent years, there has been a trend towards blurring the boundaries between desktop and professional systems.

By targeting the predominant category of users you can select a DBMS

TOPIC 2 CLASSIFICATION OF BnD

Questions studied:

1. Database classification

2. Classification of DBMS

Literature:, chapter 1, chapter 2, chapter 3.

BnDs are complex systems, and their classification can be made both for the entire BnD as a whole, and for each of its components separately. Classification for each component can be carried out according to many different criteria.

1. Database classification

1) According to the form of information presentation differentiate visual And audio systems, as well as systems multimedia. This classification shows in what form information is stored in the database and presented to users: in the form of images (symbolic text, pictures, drawings, photographs, etc.), sound, or the possibility of using different forms of displaying information.

2) By the nature of data organization Databases can be divided into unstructured(DB in the form of semantic networks), semi-structured(for example, plain text databases or hypertext systems) and structured(they require preliminary design and description of the database structure, only after that they can be filled with data). This attribute refers to information presented in symbolic form.

3) Structured databases by type of model used data are divided into hierarchical, network, relational, mixed And multi-model. The development of data processing technologies has led to the emergence post-relational, object-relational or hybrid , object-oriented , multidimensional DB.

4) By type of information stored DBs are divided into documentary And lexicographic. Among the documentary databases there are bibliographic, abstract And full text.

TO lexicographical Databases include various dictionaries, classifiers, rubricators, etc. They are usually used as reference data in conjunction with documentary or factual databases.

IN documentary DB storage unit is a document ( For example, text of law or article). Searching and issuing of documents occurs based on their content. The simplest search method is based on using descriptors – keywords from the problem area that characterize the content of the document. Their totality, extracted from the request, is compared with the document descriptors (“search pattern”). In response to the user's request, either a link to the document or the document itself is given, in which he can find the information he is interested in.

In systems factual type, the database stores information about objects of interest to the user in the subject area in the form of “facts” ( For example, biographical information about employees, data on product releases by manufacturers, etc.). In response to the user's request, the required information or a message is given that the required information is not in the database.

5) By the nature of the organization of data storage and access to it differentiate local And distributed DB.

Local database is a database intended for use by a single user. Local databases can be created by each user independently, or can be retrieved from a common database.

Distributed DB assume the possibility of simultaneous access by several users to the same information (multi-user, parallel access mode). Physically, different parts of the database can be located on different computers, but logically, from the user’s point of view, they must represent a single whole.

2. Classification of DBMS

1) By languages of communication DBMS are divided into open(use universal programming languages), closed(own languages of communication with users) and mixed.

2) By functions performed DBMS are divided into informational And operating rooms. Information DBMS allow you to organize information storage and access to it. Operational DBMS perform quite complex processing, For example, automatically allow you to obtain aggregated indicators that are not stored directly in the database, etc.

3) By scope of possible application differentiate universal And specialized, problem-oriented DBMS(have powerful expressive tools to model complex objects).

4) By "power" DBMS are divided into desktop And corporate. Characteristics desktop DBMS are relatively low requirements for technical means, focus on the end user, low cost.

Corporate DBMS provide work in a distributed environment, high performance, support for teamwork when designing systems, have developed administration tools and greater capabilities for maintaining integrity. These systems are complex, expensive, and require significant computing resources.

Table 2.1 - The most popular desktop DBMS

DBMS	Manufacturer
Visual dBase	dBase, Inc.
Paradox	Corel
Microsoft Access	Microsoft
Microsoft FoxPro	Microsoft
Microsoft Data Engine	Microsoft

Table 2.2 - Server DBMS

DBMS	Manufacturer
Oracle	Oracle Corp.
Microsoft SQL Server	Microsoft
Informix	Informix
Sybase	Sybase

5) By targeting the predominant category of users you can select a DBMS for developers And for end users.

Developer-oriented systems , must:

¾ have high-quality compilers;

¾ allow the creation of “alienable” software products;

¾ have advanced debugging tools;

¾ include means of documenting the project;

¾ have the capabilities to create efficient complex systems.

Main requirements, presented to end-user oriented systems, are:

¾ user-friendliness of the interface;

¾ high level of language skills;

¾ the presence of intelligent prompt modules;

¾ increased protection against unintentional errors (“fool proof”), etc.

3. Classification of data banks

1) According to the terms of service There are free and paid ones. Paid ones are divided into commercial and non-profit.

Non-profit databases operate on the principle of self-sufficiency and do not aim to make a profit (scientific, library or socially significant BnD).

The main purpose of creation commercial BnD is to make a profit from information activities.

2) By type of ownership BnDs are divided into state and non-state (private, group, personal).

3) According to accessibility distinguish between public and limited users .

4) By subject area coverage BnD can be classified in different “cuts”:

¾ territorial (worldwide, country, city, etc.);

¾ temporary (year, month, since the beginning of the century, etc.);

¾ departmental ;

¾ problem ( thematic ) .

5) By the nature of user interaction BnDs are divided into active and passive. IN passive BnD The leading role belongs to the user. IN active– the system can independently change behavior.

6) According to the nature of the predominant information processing distinguish between OLTP systems (On - Line Transaction Processing ) – online transaction processing systems(implement a large number of fairly simple queries) and OLAP – systems (On - Line Analytical Processing ) – analytical data processing systems(implement complex analytical data processing) or strategic decision support systems (DSS).

Until the mid-90s of the twentieth century. Databases were understood as static databases ( OLTP ). By the mid-90s in the DB class OLTP So much chronological information has accumulated that the volume of the database has increased sharply, and performance has begun to decline. For example, in the work of the dean's office, detailed data about the current academic year is most often required. At the same time, the database stores retrospective data for previous years. Such data is needed much less frequently and most often in aggregated form. For example, give out the names of students who received only excellent grades in the last three semesters.

Table 2.3 - Comparison OLTP and OLAP

Characteristic	OLTP	OLAP
Predominant operations	Data entry, search	Data analysis
Nature of requests	Lots of simple transactions	Complex transactions
Stored data	Operational, detailed	Covering a large period of time, aggregated
Kind of activity	Operational, tactical, uncomplicated processing	Analytical, strategic: forecasting, modeling, analysis and identification of connections, identification of statistical patterns
Data type	Structured	Various types
Data retention period	Up to a year	Up to several decades
Data variability	Are changing	Are being added
Organizing data	For any field	Chronologically
Volume of information processed	Small	Very big
Processing speed	Average	Very high
	Often and in small portions	Rarely and in very large portions

Separate databases can combine all the data necessary to solve one or more applied problems, or data related to any subject area (for example, finance, students, teachers, etc.). The first ones are usually called applied databases , and the second - subject databases (correlated with the objects of the organization, and not with its information applications).

Subject databases allow you to provide support for any current and future applications, since their set of data elements includes sets of application database data elements. As a result, subject databases provide the basis for processing unformalized, changing and unknown queries and applications (applications for which it is impossible to determine the data requirements in advance). Such flexibility and adaptability makes it possible to create fairly stable information systems based on subject databases, i.e. systems in which most changes can be made without having to rewrite old applications.

Discipline: Information technologies in management

Topic: Database classification

Moscow 2004

PLAN

1. Classification of DBMS.

2. DBMS functionality.

3. Database description models.

Database is an information model of a subject area, a collection of interrelated data stored together with such minimal redundancy that it can be used optimally for one or more applications. Data (files) are stored in external memory and are used as input for solving problems.

DBMS is a program that allows for centralized management of data stored in the database, access to it, and keeping it up to date.

Database management systems can be classified according to the method of establishing connections between data, the nature of the functions they perform, the scope of application, the number of supported data models, the nature of the language used to communicate with the database, and other parameters.

DBMS classification:

Based on the functions they perform, DBMSs are divided into operational and informational;

According to the scope of application, DBMSs are divided into universal and problem-oriented;

Based on the communication language used, DBMSs are divided into closed ones, which have their own independent languages for users to communicate with databases, and open ones, in which a programming language extended by data manipulation language operators is used to communicate with the database;

Based on the number of supported levels of data models, DBMSs are divided into one-, two-, and three-level systems;

According to the method of establishing connections between data, relational, hierarchical and network databases are distinguished;

Based on the way they organize data storage and perform processing functions, databases are divided into centralized and distributed.

Network-accessible centralized database systems involve two main architectures: file-server or client-server.

File server architecture. It involves the allocation of one of the network machines as a central one (the main file server), where a shared centralized database is stored. All other machines act as workstations. Database files, in accordance with user requests, are transferred to workstations, where they are mainly processed. With a high intensity of access to the same data, the performance of the information system decreases.

Client-server architecture. This model of computer interaction on a network has actually become a standard for modern DBMSs. Each of the computers connected to the network and making up this architecture plays its role: the server owns and manages the information resources of the system, the client has the opportunity to use them. In addition to storing the centralized database, the database server handles most of the data processing. A request for data issued by a client (workstation) triggers a search and retrieval of data on the server. The extracted data is transported over the network from the server to the client. A specific feature of the client-server architecture is the use of the SQL query language.

The database server is a DBMS that processes queries received from all workstations in parallel. As a rule, the client and server are geographically separated from each other, in which case they form a distributed data processing system.

The characteristics of the DBMS are:

Performance;

Ensuring data integrity at the database level;

Ensuring data security;

Ability to work in multi-user environments;

Ability to import and export data;

Providing access to data using the SQL language;

Ability to create queries;

Availability of tools for developing application programs.

DBMS performance is assessed:

Request execution time;

Speed of information retrieval;

Time to import databases from other formats;

Speed of operations (such as updating, inserting, deleting);

Report generation time and other indicators.

Data security is achieved:

Encryption of application programs;

Data encryption;

Password protection of data;

Restricting access to the database (to a table, to a dictionary, etc.).

Ensuring data integrity implies the presence of means to ensure that the information in the database always remains correct and complete. Data integrity must be ensured regardless of how the data is entered into memory (online, through import, or using a special program). Currently used DBMSs have the means to ensure data integrity and reliable security.

The database management system manages data in external memory, provides reliable data storage, and supports appropriate database languages. An important function of the DBMS is the function of managing RAM buffers. Typically, DBMSs work with large databases, often exceeding the size of the computer's RAM. Developed DBMSs maintain their own set of RAM buffers with their own discipline for replacing them.

The most widely used database management systems are Microsoft Access and Oracle.

The stages of work in the DBMS are:

Creating the database structure, i.e. determining the list of fields that make up each table record, the types and sizes of fields (numeric, text, logical, etc.), identifying key fields to ensure the necessary connections between data and tables;

Entering and editing data in database tables using the default standard table form and using screen forms specially created by the user;

Processing of data contained in tables, query-based and program-based;

Outputting information from a computer using reports and without using reports.

The named stages of work are implemented using various commands.

A centralized database provides ease of management, improved on-site data utilization for remote queries, higher processing concurrency, and lower processing costs.

A distributed database involves storing and executing data management functions across multiple nodes and transferring data between these nodes as queries are executed. In such a database, not only its different tables can be stored on different computers, but also different fragments of one table. At the same time, it does not matter to the user how the data storage is organized; he works with such a database as if it were centralized.

There are three types of database description models - hierarchical, network and relational, the main difference between which is the nature of the description of relationships and interactions between objects and attributes of the database.

Hierarchical model involves the use of tree structures consisting of a certain number of levels to describe the database. A "tree" is a hierarchy of elements called nodes. Elements mean a list, a collection, a set of attributes, elements that describe objects.

An example of a simple hierarchical structure is the administrative structure of a higher education institution, the elements of which are: “University – Faculty – Group”. At each level of the hierarchy of a given structure, different attributes can be used. For example, attributes of the third level can be: group specialization, numerical composition, surname of the group leader, and others.

In this model there is a root node or simply a root - “University”, which is at the highest level of the hierarchy, and therefore has no nodes above it. Each node of the model has only one initial one, located in relation to it at a higher level, and at subsequent levels of classification it can have one, two or more nodes, or not have them at all.

Hierarchy principles:

The hierarchy always starts at the root node (or master node);

The original node from which a tree is built is called a root node or simply a root, and one tree can only have one root;

A node can contain one or more attributes that describe the object it contains;

The generated nodes can be embedded in the “tree” both horizontally and vertically;

Child nodes can only be accessed through the source node, so there is only one access path to each node.

The advantage of the model is the simplicity of its construction, ease of understanding the essence of the hierarchy principle, and the availability of industrial DBMSs that support this model. The disadvantage is the complexity of operations to include information about new database objects into the hierarchy and delete outdated information.

Network model describes elementary data and the relationships between them in the form of a directed network. These are relationships between objects when each generated element has more than one parent element and can be associated with any other element of the structure. For example, in the management structure of an educational institution, the generated element “Student” may have not one, but two initial elements: “Student – Study Group”, and “Student – Dorm Room”.

Network structures can be multi-level and have varying degrees of complexity. A circuit that has at least one many-to-many relationship and requires complex methods to be implemented is a complex circuit.

The database described by the network model consists of areas, each of which consists of records, and the latter, in turn, consists of fields. The disadvantage of the network model is its complexity and the possibility of losing data independence when the database is reorganized. With the appearance of new users, new applications and new types of queries, the database grows, which can lead to disruption of the logical representation of data.

Relational model is based on the concept of “relationships”, and its data is formed in the form of tables. A relation is a two-dimensional table, which has its own name, in which the minimum action object that preserves its structure is a table row (tuple), consisting of table cells - fields.

Each table column corresponds to only one component of this relationship. From a logical point of view, a relational database is represented by many two-dimensional tables of various subject content.

Depending on the content, the relationships in a relational database are objective and coherent. Objective relations store data about any one object, an instance of an entity. In them, one of the attributes uniquely identifies the object and is called the relation key or primary attribute (for convenience, it is written in the first column of the table). The remaining attributes are functionally dependent on this key. Objectively, there cannot be duplicate objects, and this is the main limitation of a relational database. A linked relation stores the keys of several object relations through which connections are established between them.

If the set of database attributes is not fixed in advance, then various options for grouping them are possible, however, regardless of the chosen method, the same requirements must be met. In particular, if the database contains many relationships, then they should have minimal redundancy in the representation of information; the attributes included in the database must support mass calculations; When new attributes are added to the database, rearrangement of relationship sets should be minimal.

The advantages of the relational model include: simplicity of construction, ease of understanding, the ability to operate a database without knowledge of the methods and methods of its construction, data independence, flexibility of structure, and others. The disadvantages of the model are: low performance compared to hierarchical and network models, software complexity, redundancy.

LITERATURE

1. Veretennikova E.I., Patrushina S.M., Savelyeva N.G. Computer Science: Textbook. Series "Training Course". – Rostov n/d: Publishing center “MarT”, 2002.

2. Mogilev A.V. Informatics: Textbook. aid for students ped. universities / A.V. Mogliev, N.I. Park, E.K. Henner; Ed. E.K. Henner. - 2nd ed., erased. – M.: Publishing Center “Academy”, 2003.

Tutoring

Need help studying a topic?

Our specialists will advise or provide tutoring services on topics that interest you.
Submit your application indicating the topic right now to find out about the possibility of obtaining a consultation.

Introduction

Chapter 1. Database Basics

1.1. Classification of databases

1.3 Database description models

1.4. Basics of desktop DBMS

1.5. Requirements and standards for databases

Chapter 2. Working with a Microsoft Access database

2.1. Basics of the desktop DBMS Microsoft Access

2.2. Working with a Microsoft Access database

Conclusion

List of used literature

Introduction

The flows of information circulating in the world that surrounds us are enormous. In

over time they tend to increase. Therefore, in any organization, like

big and small, the problem of such management organization arises

data that would ensure the most efficient operation. Some

organizations use filing cabinets for this, but most prefer

computerized methods - databases that allow efficient storage,

structure and systematize large volumes of data. And today without bases

data it is impossible to represent the work of most financial, industrial,

trade and other organizations. Without databases, they would simply drown in

information avalanche.

There are many good reasons to transfer existing information to a computer basis. Now the cost of storing information in computer files is cheaper than on paper. Databases allow you to store, structure information and retrieve

in an optimal way for the user. This topic is relevant at present, because... the use of client/server technologies allows you to save significant funds, and most importantly, time to obtain the necessary information, and also simplify access and maintenance, since they are based on comprehensive data processing and centralization of their storage. In addition, the computer allows you to store any data formats, text, drawings, handwritten data, photographs, voice recordings, etc.

To use such huge volumes of stored information, in addition to the development

system devices, data transmission media, memory, necessary means

ensuring human-computer dialogue that allows the user to enter

or make decisions based on stored data. To provide these functions

specialized tools have been created - database management systems (DBMS).

The purpose of this work is to reveal the concept of a database and database management system, and also to consider the operation of a desktop DBMS using a specific example.

1.1. Classification of databases

A database is an information model of a subject area, a collection of interrelated data stored together with such minimal redundancy that it can be used optimally for one or more applications. Data (files) are stored in external memory and are used as input for solving problems.

A DBMS is a program that implements centralized management of data stored in a database, access to it, and keeping it up to date.

DBMS classification:

· according to the functions performed, DBMSs are divided into operational and informational;

· according to the scope of application, DBMSs are divided into universal and problem-oriented;

· according to the communication language used, DBMSs are divided into closed ones, which have their own independent languages for users to communicate with databases, and open ones, in which a programming language extended by data manipulation language operators is used to communicate with the database;

· according to the number of supported levels of data models, DBMSs are divided into one-, two-, and three-level systems;

· according to the method of establishing connections between data, relational, hierarchical and network databases are distinguished;

· Based on the way they organize data storage and perform processing functions, databases are divided into centralized and distributed.

Network-accessible centralized database systems involve two main architectures: file-server or client-server.

1.2. DBMS functionality

The characteristics of the DBMS are:

· productivity;

· ensuring data integrity at the database level;

· ensuring data security;

· ability to work in multi-user environments;

· ability to import and export data;

· providing access to data using the SQL language;

· ability to create queries;

· Availability of tools for developing application programs.

DBMS performance is assessed:

· request execution time;

· speed of information retrieval;

· time of importing databases from other formats;

· speed of operations (such as updating, inserting, deleting);

· report generation time and other indicators.

· Data security is achieved:

· encryption of application programs;

· data encryption;

· data protection with a password;

· restriction of access to the database (to a table, to a dictionary, etc.).

The most widely used database management systems are Microsoft Access and Oracle.

The stages of work in the DBMS are:

· creating a database structure, i.e. determining the list of fields that make up each table record, the types and sizes of fields (numeric, text, logical, etc.), identifying key fields to ensure the necessary connections between data and tables;

· entering and editing data in database tables using the standard form presented by default in the form of a table and using screen forms specially created by the user;

· processing of data contained in tables, based on queries and based on the program;

· outputting information from a computer using reports and without using reports.

The named stages of work are implemented using various commands.

A centralized database provides ease of management, improved on-site data utilization for remote queries, higher processing concurrency, and lower processing costs.

1.3.Models for describing databases

Hierarchy principles:

· hierarchy always starts from the root node (or main node);

· the source node from which the tree is built is called the root node or simply the root, and one tree can have only one root;

· a node can contain one or more attributes that describe the object located in it;

· generated nodes can be built into the “tree” both horizontally and vertically;

· child nodes can only be accessed through the source node, so there is only one access path to each node.

Each table column corresponds to only one component of this relationship. From a logical point of view, a relational database is represented by many two-dimensional tables of various subject content.

1.4. Desktop DBMS

Desktop DBMSs differ in that they use a network and file server computing model (file-server architecture). The increasing complexity of tasks, the emergence of personal computers and local area networks were the prerequisites for the emergence of a new “file-server” architecture. This network-accessible database architecture involves designating one of the computers on the network as a dedicated server on which database files will be stored. In accordance with user requests, files are transferred from the file server to user workstations, where the bulk of data processing is carried out. The central server mainly performs only the role of file storage, without participating in the processing of the data itself.

The work is structured as follows:

The database in the form of a set of files is located on the hard drive of a specially dedicated computer (file server). There is a local network consisting of client computers, each of which has a DBMS and an application for working with the database installed. On each of the client computers, users have the ability to run the application. Using the user interface provided by the application, it initiates a call to the database to retrieve/update information.

All calls to the database go through the DBMS, which encapsulates within itself all the information about the physical structure of the database located on the file server. The DBMS initiates calls to data located on the file server, as a result of which part of the database files is copied to the client computer and processed, which ensures the fulfillment of user requests (the necessary operations on the data are carried out). If necessary (if data changes), the data is sent back to the file server to update the database. The DBMS returns the result to the application. The application, using the user interface, displays the result of the queries. Within the framework of the “file-server” architecture, the first versions of the popular so-called. desktop DBMSs such as dBase and Microsoft Access.

The following main disadvantages of this architecture are indicated: when many users simultaneously access the same data, performance drops sharply, because it is necessary to wait until the user working with the data completes his work. Otherwise, corrections made by some users may be overwritten by changes made by other users.

Today, more than two dozen desktop DBMS data formats are known, but the most popular, based on the number of copies sold, are dBase, Paradox, FoxPro and Access. Of the recently appeared DBMSs, one should also note Microsoft Data Engine - essentially a server DBMS, which is<облегченную>version of Microsoft SQL Server, but intended, however, for use primarily on desktop systems and small workgroups.

	Manufacturer
		http://www.dbase2000.com/
		http://www.corel.com/
Microsoft Access 2000		http://www.microsoft.com/
Microsoft FoxPro		http://www.microsoft.com/
Microsoft Visual FoxPro		http://www.microsoft.com/
Microsoft Visual FoxPro		http://www.microsoft.com/
Microsoft Data Engine		http://www.microsoft.com/

1.5. Requirements and standards for databases

The following basic requirements apply to modern databases, and, consequently, to the DBMS on which they are built:

· High performance (short response time to a request).

To create a new database using the wizard, follow these steps:

Execute the File [New] command

In the “Create” dialog box that opens, select the “Databases” shortcut. A list of databases offered by the wizard will appear on the screen. This list is very large and can reach several dozen different options that can be used immediately or will serve as the basis for building other databases. For example, “Work Orders”, “Invoices”, “Contacts”, “Events”, ... etc.

Select the sample database that suits you from the list and run the database creation wizard by clicking OK.

In the “New Database File” dialog box that opens, from the Folder drop-down list, select the folder in which you want to save the database being created, and enter its name in the File name field. Then click the Create button.

In the next dialog window, the wizard tells you what information the database it creates will contain. At the bottom of this dialog box are the following buttons:

Cancel - stops the wizard;

Back - allows you to return to the previous step in the wizard;

Finish - launches the database creation wizard with the selected parameters, and before clicking this button, the information that will be stored in the database is displayed.

The dialog box that opens contains two lists. The first one is a list of database tables, and the second one is a list of fields of the selected table. This list indicates the fields that will be included in the table. Usually almost all table fields are checked, with the exception of fields that are used quite rarely. By checking or unchecking fields, you can select the table fields. Once you have selected the table fields, click Next.

In the next dialog window, select a screen design type from the proposed samples and click Next (at the same time, the screen offers you the opportunity to preview screen design types, which you can sort through in the right window of the dialog window).

At the next step of the wizard, you can determine the type of reports to be created for the database. After selecting the type that suits you, click Next (here you are also invited to first familiarize yourself with the possible options, which you can also sort through).

The Database Creation Wizard dialog box that then opens allows you to specify its title and image (for example, a company trademark) that will appear in all reports. If you decide to use a picture, check the Yes box. In this case, the Picture button becomes available, clicking on which opens the “Select Picture” dialog box for selecting a file with a picture that you created in advance. Click Next to make further settings.

By clicking the Finish button in the last dialog window, you launch the wizard to build a database with the specified parameters. Using the Back button, you can return to any of the previous steps and change database parameters. You can click the Finish button in any wizard dialog window, refusing to further set additional parameters. In this case, the wizard uses the default settings in its work.

After clicking the Finish button, the wizard proceeds to creating a database consisting of tables with the fields you specify, simple forms for entering and viewing information, and simple reports. After completing the database creation process, you can immediately use the finished database: enter data into tables, view it and print it.

If the options for the proposed databases do not suit you, then you can create an empty database and add tables, queries, forms and reports to it.

So, you begin to create database tables into which information will subsequently be entered. In the future, the data in the table can be supplemented with new data, edited or excluded from the table. You can view data in tables or organize it according to certain criteria. The information contained in the tables can be used to generate reports. In addition, you can give a graphical interpretation of the information contained in the database. You will learn how to solve these problems in subsequent chapters.

Creating a table in MS Access is done in the database window. Let's look at the sequence of your actions when creating a table in a new database:

Open the window of the database you created and go to the “Tables” tab.

Click the Create button in the database window.

The “New Table” dialog box will open, on the right side of which there is a list of options for further work:

Table mode - allows you to create a new table in table mode;

Designer - allows you to create a new table in the table designer;

Table Wizard - allows you to create a new table using the wizard;

Import tables - allows you to import tables from an external file into the current database;

Linking with tables - allows you to create tables linked to tables from external files.

Select the table creation option that suits you from this table and click OK.

Create a table structure using the tool of your choice. You can create a table using the wizard and using the designer.

To associate a table with the information it contains, each table is given a name. Set the table name in the “Save” dialog box and click OK.

When naming a table, like a database name, you are not limited to eight characters. The table name, like the names of other database objects, is stored in the database itself.

The field name is entered in the input field of the field name column. When specifying field names, you must follow the following rules:

The field name can contain up to 64 characters, but you should not abuse this feature by specifying too long names;

The field name can contain letters, numbers, spaces and special characters, with the exception of period (.), exclamation point (!), straight brackets () and some control characters (ASCII codes 0-31);

The field name cannot begin with a space;

Two fields in the same table cannot have the same names;

Non-compliance with these rules is monitored by MS Access DBMS, but in some cases this can lead to difficult-to-identify errors, so it is recommended to independently monitor compliance with the above rules in practical work.

It is advisable to try to use names that are short to make them easier to identify when viewing tables.

Text;

Numerical;

Monetary;

Counter;

Dates/times;

Logical;

MEMO field:

OLE object field;

Master of substitutions.

Text fields can contain letters, numbers, and special characters. The maximum field width is 255 characters.

To change the field width, in the Field Size line of the “Field Properties” section, set a number that determines the field width (from 1 to 255).

Each data type has its own properties, which are displayed in the “Field Properties” section of the designer window.

Now that we've looked at the data types in Access and the individual table field properties, we can begin creating the table structure. Let's look at creating a table structure using the example of creating the Orders table in the Northwind database supplied with Access. This table already exists in the Northwind database, but reviewing the process of creating this table will be very useful. In order not to disrupt the structure of the Borei database, first create a training database and open its window.

In the table designer window, in the Field Name column, enter Order Code.

Press Tab or Enter to move to the Data Type column. Please note that information appears in the “Field Properties” section at the bottom of the dialog window.

The Data Type column now has the value Text. Click on the expand list button on the right side of the rectangle and you will see a list containing all data types. From this list, use the mouse or the up and down keys to select the Counter value and press the Tab key to move to the Description column. The Description column is the explanation you give for your fields. When you work with this table in the future, this description will appear at the bottom of the MS Access screen whenever you find yourself in the Order Code field, and will remind you of the purpose of this field.

Enter explanatory text in the Description column and press Tab or Enter to move on to entering information about the next field. Enter a description of all table fields in the same way. Once you have completed entering the table structure, save it by using the File/Save command.

Create a table in Datasheet view

We've looked at two ways to create tables, now let's move on to the third. Each method has its own advantages and disadvantages. But we are sure that this method of creating a table will amaze you with its simplicity, clarity and you will really like it. It is not for nothing that it is located first in the list of methods for creating tables in the “New Table” dialog window. You will probably use it most often.

Below is the sequence of actions you have to perform:

Go to the “Tables” tab of the database window and click the Create button.

In the New Table dialog box, select Table Mode from the list of options and click OK. As a result of performing these actions, the “Table” dialog box will open, containing the default table created. This table contains 20 columns and 30 rows, which is enough to get you started. After saving this table, you can, of course, add as many rows and columns as you need.

The table field names are defined by default, but they are unlikely to satisfy your requirements. MS Access makes it very easy to assign new names to fields. To do this, double-click on the selection area of the first field (the title of which contains Field 1). The field name is highlighted and a blinking cursor appears. Type a name for the first field and press the Tab key. Similarly, enter the remaining field names of your table in the following columns.

Now fill out a few rows of your table, entering the information in the form in which it will be entered in the future. Try to write everything in the same style (for example, if you wrote down the first date as 10/14/09, then do not write the next one as November 3, 2009). If MS Access sets the wrong data type, you can change it, but it is better to enter everything correctly at once.

Save the table by running the File/Save Layout command or by clicking the Save button on the toolbar. In the “Save” dialog box that opens, give the table a name and click OK.

When prompted to create a primary key for the table, click Yes, and MS Access will create the table, removing unnecessary rows and columns.

Now make sure that Access has selected the correct data types for each field. To do this, go to the table designer window by executing the View/Table Designer command. If you are not satisfied with something in the table structure, make the necessary changes.

In the previous chapter we looked at the use of filters, and in this chapter we will look at a more powerful means of retrieving data - queries.

In practice, it is often necessary to select from the source table a subset of records that meet certain criteria and order the selection. The criteria may be determined by a combination of a number of conditions. For example, you need to select records about suppliers of a certain product from Minsk and arrange them in alphabetical order by company name. Query wizards and a query designer are designed to solve such problems, with which you can:

Generate complex criteria for selecting records from one or more tables;

Specify the fields displayed for the selected records;

Perform calculations using selected data.

What is a “Sample Request”

Previously, we reviewed general provisions related to databases, where we noted that one of the main purposes of databases is to quickly search for information and obtain answers to various questions. Questions formulated in relation to the database are called queries. In MS Access, to form queries, the query designer and the SELECT statement of the MS Access language are used.

What is a “Sample Request”? A pattern query is an interactive tool for selecting data from one or more tables. When creating a query, you need to specify the criteria for selecting records in the source table. In this case, instead of typing sentences in a special language, you must simply fill out the request form, which is located in the request designer window. The method of creating a request by filling out a form is easy to learn and understand. It facilitates the effective use of MS Access capabilities by users who have even minimal or no experience with the application.

All necessary information is located in the Clients table of the Borei database. Therefore, to create a request, follow these steps:

In the database window, go to the “Queries” tab and click the Create button.

The order of the fields in the query form determines the order in which they appear in the resulting table. To change the location of a field in this list, follow these steps:

Place your mouse pointer over the column selection area, which is located directly above the field name. When the pointer changes to an arrow, click the button to highlight the column.

Click and hold the mouse button in this position. A rectangle will appear at the end of the pointer.

Move the column in the desired direction. A thick vertical line will show its current position.

Release the button when the thick vertical line is in the desired location. The field will be moved to a new location.

Move a request form column. Sometimes it is not immediately possible to select a column to move. Make sure you click the column selector area (the small rectangle that is directly above the field name). This is the only place where you can grab a column for transfer. To transfer a field to the request form, double-click on the field name

Select Auto Report.

A ready-to-use report will appear on the screen in a matter of seconds. This report includes all table fields. Their names are arranged vertically in volume the same order in which they are in the table. To the right of the name of each field its value is displayed in the table.

Conclusion

This course work examined the concept of a database and a database management system, with the help of which centralized management of data stored in the database is implemented, access to it, and keeping it up to date. So, a database is a collection of interrelated data stored together in one or more computer files. We also looked at working with one of the popular DBMSs, Microsoft Access.

The Microsoft Access DBMS provides the necessary tools for working with databases to the inexperienced user, allowing him to easily and simply create databases, enter information into them, process queries and generate reports. Unfortunately, the built-in help system does not clearly explain the operation procedure to a novice user, so there is a need for a manual.

Marchenko A.P. Microsoft Access: A short course. – St. Petersburg: Peter, 2005. – p. 56

Lazarev I.P.. “Microsoft Access for Dummies”.. St. Petersburg - Peter, 2004. - p. 139.

Lazarev I.P. “Microsoft Access for Dummies.” St. Petersburg - Peter, 2004. - p. 196.

Marchenko A.P. Microsoft Access: A short course. – St. Petersburg: Peter, 2005. – 239.

Articles By topic:

Nobody's thing. Sean Tan. Nobody's Thing Books by Sean Tan, translated into Russian “I guess you want to know what this book is about just by reading the cover? I get it—everyone is short on time, there’s a lot to do, and most of us probably have more important things to do than look at a picture book about a giant red thing, lost.	Artificial intelligence (AI) The Turing Test, proposed by Alan Turing, was developed as a satisfactory functional definition of intelligence. Turing decided that there was no point in developing an extensive list of requirements needed to create artificial intelligence.
By the nature of the information stored Database For example: Factual documents presented in a strictly defined format.	Documentary ) Information storage input procedure search - the process of processing a request; Most of the words we use in everyday life have certain meanings. But there are also terms whose meaning cannot be clearly explained. Let's try to explain what quintessence is. This word often appears in various

Popular

2024-05-17 02:59:06	B2C sales: how to apply and where Basic B2C sales techniques
2024-05-17 02:59:06	What is the binary number system?
2024-05-16 02:18:18	Protocol in modern office work
2024-05-16 02:18:18	What planets are visible from earth
2024-05-16 02:18:18	Topic: Scientific style of speech
2024-05-15 02:18:06	What a bartender should know
2024-05-15 02:18:06	Open integrated lesson in the middle group “Tasks of Baba Yaga Notes of integrated lessons in the middle group of doe
2024-05-14 02:18:11	Pumpkin: benefits and harm to the body
2024-05-14 02:18:11	Instructions. FPI test. Freiburg Multifactor Personality Questionnaire. Methodology for personality research Scale XI – emotional lability
2024-05-14 02:18:11	Editor-in-Chief of the magazine "Hunting" Valery Kuzenkov told "Russian Planet" why the country's fauna has become so impoverished

New

2024-05-13 02:17:14	Fertilization of horsetails. Horsetails. Horsetail: properties and contraindications
2024-05-13 02:17:14	Heat generation and release Heat is generated to a greater extent
2024-05-13 02:17:14	Biology at the Lyceum For what purpose does a person use vegetative propagation?
2024-05-13 02:17:14	Description, features, types and properties of horsetail
2024-05-13 02:17:14	Levels of organization and function of proteins
2024-05-13 02:17:14	Structure of the respiratory organs
2024-05-17 02:59:06	Nobody's thing. Sean Tan. Nobody's Thing Books by Sean Tan, translated into Russian
2024-05-17 02:59:06	Artificial intelligence (AI)
2024-05-17 02:59:06	By the nature of the information stored
2024-05-17 02:59:06	Definition of the concept, where it is used and where the word came from. Quintessence meaning of the word.
2024-05-17 02:59:06	B2C sales: how to apply and where Basic B2C sales techniques
2024-05-17 02:59:06	What is the binary number system?