Areas of application of databases in economics
Automated information systems (AIS), which are based on databases, appeared in the 60s in the military industry and in business, where significant volumes of useful data were accumulated. Initially, automated information systems were focused only on working with information of a factual nature - numerical or textual characteristics of objects. Then, with the development of technology, it became possible to process textual information in natural language.
The principles of storing different types of information in AIS are similar, but the algorithms for its processing are determined by the nature of information resources. Accordingly, two classes of AIS were distinguished: documentary and factual.
Documentary AIS is used to work with documents in natural language. The most common type of documentary AIS is information retrieval systems designed for the accumulation and selection of documents that meet the specified criteria. They can view and select monographs, publications in periodicals, press agency reports, texts of legislative acts, etc.
Factographic AIS operate with factual information presented in a formalized form. Factographic AIS is used to solve data processing problems.
Data processing is a special class of computer-solved tasks related to the input, storage, sorting, selection and grouping of data records of a homogeneous structure. The tasks of this class are solved when accounting for goods in stores and warehouses, payroll, production management, finance, telecommunications.
Distinguish between factual AIS of operational data processing, implying fast service of relatively simple requests from a large number of users, and factual AIS of analytical processing, focused on fulfilling complex queries.
Principles of operation of the Microsoft Access DBMS
Microsoft Access is an interactive relational database management system (RDBMS) for WINDOWS. It is a program that you can use to store and retrieve data depending on the relationships that you have established. Working with it is simplified by means of a mouse manipulator. The graphical capabilities of the shell are impressive for producing high quality reports and printouts. All this thanks to support for True-type fonts and embedding of OLE-objects (Object Linking and Embeding) within the framework of the WINDOWS environment. OLE - an object is a link to certain information that remains in its original form. An OLE object can be an EXCEL table, a Paintbrush illustration, or a Sound file.
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Access also provides the user with mechanisms for working with databases of various formats. For example, you can directly access dBASE, Paradox, or Btrieve databases without converting them to the format used by Access. The Access package also includes the Access Basic language (a built-in dialect of the Visual Basic language), which makes it possible to form specialized database management systems.
The basic concepts or objects of this system are: tables, queries, forms, reports, macros and modules. And, of course, the main concept will be the database (database).
To create a database, follow these steps:
Activate the Microsoft Access window and select the New Database directive from the File menu (or click the New Database button in the icon bar). Microsoft Access displays the New Database dialog box and automatically gives the database a name that can be replaced.
In the File Name line, print a variant of the database name. It can contain up to 8 characters without spaces. Microsoft Access automatically adds the MDB extension to the database name.
To store the database in a specific location, select the appropriate directory in the Directories list.Click the OK button.
Microsoft Access creates an empty database file and opens the Database window.
The database can be filled with objects of various kinds and perform operations with them. But with the database, you can perform operations as an indivisible entity. All operations of this kind - database management operations - are concentrated in the File menu of the Access application window or in the database window.
When opening a database, you can restrict possible operations with the database to read-only and restrict the range of users who have access to the database only by their own person. If you only want to view the database and the objects it contains, but not modify them, then when you open the database, you must activate the Read Only watchdog. If it is necessary to prevent changes to the data and objects of this database by other users, then when opening the database, you must set the Exlusive option.
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If the user has finished working with the database, then it should be closed using the Close Database directive in the File menu, by double-clicking Click on the button to call the control menu of the database window or by pressing the keys (Ctrl + F4).
Tables.
The next step in building the database will be filling it, that is, creating objects and assigning the latter the necessary properties. Whatever type of data you have, you will have to store it in one or more tables.
Tables are the main form of presentation of information contained in a database. A form cannot be designed without a table; queries and reports are based on tables.
Each field included in a record is assigned a data type that determines the type of information that will be stored in this field. The data type is entered in the Data Type column, and it can be selected from the list of available types.
You can make changes to the finished specification. But at the same time, you should try to make all the corrections to the specification before filling the database, since an attempt to change the parameters of the fields of the filled database may result in data loss or corruption.
You can embed objects from other OLE-capable applications into Access tables and associate these objects with their parent programs.
When you embed an object, Access stores the object in a table. Double-clicking on the object starts the application program with which it was made - you can make changes to the object in it. After finishing work with the parent program, the object in the modified form will be saved in the table.
You can import tables that are in a database created by another program into Access, or you can export Access tables, saving them in formats that other database applications can understand. But before proceeding directly with the import or export, it is necessary to make the appropriate import or export settings.
Requests.
Queries are used to select and filter a dataset. They allow you to select from the database only the necessary information, that is, the one that meets a certain criterion (condition) and is needed to solve a specific problem. For example, you may need information about suppliers and the goods they supply. You can create a query like "What goods are supplied by Moscow suppliers" or "Which of the St. Petersburg suppliers of cigarettes sold the largest batch in the last quarter". The result of Access processing such a query is a table called Dynaset. This table includes data blocks selected from the main table (or multiple tables) that meet the query criteria. Dynaset is a dynamic, temporary dataset, so it is rebuilt on the basis of "fresh" tabular data each time a query is executed.
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There are two types of requests:
QBE queries (Query by Example). The user defines them by specifying individual parameters in the design window using prompts (samples).
SQL - queries (Structured Query Language - Structured Query Language). The user formulates them using instructions and functions, building a description. Access easily translates the QBE query into the corresponding SQL query. The reverse operation is also easy. In general, Access doesn't care what type of query the user is working with.
Queries can be created using the Query Builder as well as without the Query Builder. However, the first method speeds up the design of several custom query types.
Selection criteria are instructions by which the user tells Access which blocks of data should be fetched upon request and displayed in Dynaset. Criteria can be specified for one or more query fields.
The user can use the request to perform calculations with data blocks. He can define in each field some function that processes the contents of this field. The processing result is sent to Dynaset. The processing function is set in the Total line, which appears after clicking the button with the Greek letter "sigma" in the pictographic menu. The function itself can be selected in this line by expanding the list of possible values.
Once the query is designed, it can be run by clicking on the exclamation mark button in the icon bar or by calling the Run directive on the Query menu. Access displays the blocks selected on request in Dynaset in the form of a table.
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Using the structured SQL query language within Access, the user can formulate queries that are arbitrarily complex in terms of the structure of criteria and calculations. The same language allows you to control the processing of requests. An SQL query is a sequence of statements that can include expressions and calls to aggregate functions.
If the user wants to have the developed project request at his disposal during the next sessions, he must save it using the Save directive in the File menu. If the project is saved for the first time, then after referring to this directive, the Save As dialog box will appear. In it, you should assign a name to the request, under which m it will be saved and included in the list of requests in the databank window. The query name must not be the same as the table name.
If the given request has already been saved once and the user has selected the Save directive, then the old version will be replaced by the new, modified request project. If the changes should not spoil the previous version, but should be saved in another request, then you should call the Save As directive and assign a new name to the saved project. To save the table view of a query, select the Save Query directive from the File menu. This directive saves changes to the project of an existing request and replaces the previous version of the request with the active version. To save a query for the first time or to create a copy of an active query, the Dynaset of which is visible on the screen, you should select the Save Query As directive.In addition to selection queries, you can also implement action queries, parametric queries, and crosstab queries with Access.
CONCLUSION
Modern database management systems such as IMS, Lotus Approach, Cetop, Oracle, Clipper, FoxPro, Access are really powerful tools for managing large amounts of data. They allow for quick sorting of a large data set, for quick navigation through records in random order, for quick selection of a large amount of data from the entire data set according to specified criteria. In such DBMS, each data file is considered as a two-dimensional table, the columns of which correspond to the fields of the records, and the rows correspond to the individual records of the file, and the data is accessed by specifying the record number of the field name. At the same time, working with a separate field of a data table resembles working with variables - access to data is simplified as much as possible, and the user does not need to know the entire hierarchical data structure.
In addition, the command language of these database management systems contains a wide range of commands that perform complex actions, for example, sorting file records is reduced to only two commands. In addition, they provide commands for creating a light menu for organizing a direct dialogue with the user. All this makes writing programs as easy as possible and confirms that modern database management systems are indeed a powerful tool for creating and processing large databases.
REFERENCES
1. Informatics. Basic course / Simonovich S.V. and others - St. Petersburg: Publishing house "Peter", 2006.
2. Digo S.M. Databases: design and use. Textbook for universities. - Moscow: Finance and Statistics, 2005.
3. Agibalov A.V., Goryukhina E.Yu. Automated systems for processing economic information. Textbook - 3rd ed., Add .: Voronezh: VGAU, 2000.
4. Computer workshop. Programming in Turbo-Pascal environment and DBMS like Fox. Methodical instructions for the implementation of the course project. / Comp .: O. N. Leonova, I.A. Nesmeyanov; GAU, M., 1998.
5. Lemashko E.V., Romanchukov V.G. Programming in the Fox Family DBMS Command System: a tutorial / GAU, M., 1998.
6. Golitsina O.L., Maksimov N.V., Popov I.I. Databases: Tutorial. - M .: FORUM: INFRA-M, 2003.
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