Approaches to DB construction, Ascending and descending DB design - Databases

Approaches to building a database

They are based on two approaches to the creation of an automated control system (ACS). The first of these, widely used in the 1980s and therefore named classical ( traditional ), is related to the automation of document management (a set of documents moving in the process of the enterprise). The initial and output coordinates were the documents, as can be seen from Example 2.1. Transformation of input documents to the output is performed by the conversion algorithm.

Example 2.1. The task is as follows. There is a system of manual documents, the form of one of which is shown in Table. 2.1. It is necessary with the help of the database to get - according to regulations or on request - information in the form of another system of documents, the form of one of which is given in Table. 2.2.

Table 2.1

Student

Group number

Gradebook number

Number of student card

Last name

Address

И4

I-99/12

I-99/12

Petrov

Cash rush, 5

FROM

I-9X/1

I-98/1

Ivanov

Nevsky Prospekt 7, Apt. 3

Table 2.2

List of students in group I4

Gradebook number

Last name

I-99/12

Petrov

I-99/17

Sergeyev

The following thesis was used. The data is less mobile than the algorithms, so you need to create a universal database, which can then be used for any algorithm. However, it soon became clear that the creation of a universal database is problematic. Until recently, the concept of data integration, which had prevailed until recently, proved to be untenable. Moreover, applications began to appear (for example, text, graphic editors), based on widely used standard algorithms. The standard algorithms were also found in management (business), as it follows from Example 2.2.

Example 2.2. We use the computer to support the decision-making process of the manager in the process of accepting specialists for work (staffing the research firm). Some people are already working (in the staff of the firm), it is necessary to carry out pre-staffing. On the basis of personal data on applicants for vacancies in the staffing table, the computer, in accordance with the system of rules laid down by the designer, issues decisions to the manager on the positions to be taken by the applicants. The final decision remains with the manager.

If the manager doubts the correctness of the solution received by the computer, he can request an explanation in the form of a system used to solve the rules.

If the number of people recommended for admission exceeds the number of vacancies in the staffing table, the manager can adjust either the rules (the quantitative component) or the results of their work. The manager's decisions are entered into the computer.

The listed procedures take place on each of several (by default - of three) time intervals (cycles).

Finally, the computer displays the final results of the manager's work. This example is implemented on a computer and is described in detail in Ch. 15.

By the 90s of the XX century. a second, modern approach, related to automation of management, was formed. It involves the initial identification of standard application algorithms (business algorithms in foreign terminology), under which data are determined, and hence the database. Object-oriented programming only strengthened the importance of this approach. The composition of the database for different approaches is shown in Fig. 2.4.

Schematic of the classical (a) and modern (b) approach for building a database

Fig. 2.4. The scheme of the classical ( a ) and modern ( b ) approach in building the database

In the operation of the database, single-user and multi-user modes are possible. In the latter case, several users connect to the same computer through different ports.

Ascending and descending database design

The first is used in distributed databases when integrating the projected local databases, which can be performed using different data models. More characteristic for centralized databases is top-down design.

In the following sections, the classical approach for the centralized database will be initially considered, and then the modern one. A distributed database is devoted to Ch. 10-12 of this work.

Working with databases can be presented in the form of the scheme shown in Fig. 2.5. It shows that it is necessary to distinguish the methodology of creation, the methodology of use and the methodology for the operation of the database. The methodology of the database is defined in the design procedure, but it also manifests itself in the usage procedure.

Stages of creating (Cl, C2) and using (И1 - ИЗ) БД

Fig. 2.5. Stages of creation (Cl, С2) and use (И1 - ИЗ) of a DB

7. Data Warehouse - a subject-oriented, integrated, time-bound and unchanging data set designed to support decision making [2, 3, 17]. In accordance with the definition, the data store is not oriented to the application algorithm, as an (operational) database, but to the domain.

Integration is determined by the fact that data sources can be multiple databases that can have different data formats and the degree of database coverage. This data must be returned to the & quot; standard & quot; used in the CD.

Snap to time means that the original data characterizes a certain time interval, while the time is present in the database explicitly. Because of this, the incoming data does not change the previous data in the CD, but complements them.

Consider the methodological aspects of the database and CD.

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