Interaction with the database, Types of databases...

Interaction with the database

A typical DBMS is never visible to a database user; it does not have a graphical user interface ( Graphical User Interface , GUI for short), but only issues or writes data in response to requests submitted in the appropriate command language. The most common command language is SQL, or Stmetured Query Language , which we will consider below. The DBMS must be used in combination with an application that provides the user interface, usually a set of forms with text fields for data entry, and buttons or menus for performing various actions.

The interface can be provided with an automatic machine for selling train tickets, a cash register, a bar code reader, or perhaps an eye tracking device that collects data for psycholinguistics experiments. The database model makes it possible to use either of these interfaces or several interfaces simultaneously with the same set of data. The data type for the end user can be very different from the tables used by the DBMS for data storage. The presentation of the data should be understandable and informative for the user: data from several tables can be combined and different fields can be hidden when they are not relevant. The interface can give the user much more than just a way to view and edit data.

The interface can be implemented as an application for MS Windows , is installed on the user's desktop computer. But an extremely popular alternative is the combination of DBMS with the creation of web pages on the fly, which provides Internet access to the database. End users use a web browser to view the pages generated by the remote web server. A computer program (for example, written in PHP ) interprets user actions by querying data as required from the DBMS, and formats the results for display in the browser. The web server and DBMS can be located on the same server or on different computers - it does not matter, since the web server has access to the data only through the DBMS, and the user has access to the data only through the web server.

In Fig. Figure 13.1 shows a typical LAMP technology (operating system Linux + web server Apache + DBMS MySQL + programming language PHP ) .

LAMP Technology

Fig. 13.1. LAMP technology

Database Types

The general purpose database management systems are based on some formal, common data organization model. The most common type of database today is the so-called relational database. All popular DBMSs are relational databases, including Oracle , MySQL, Postgres, FileMaker Pro and Microsoft Access .

1. The simplest type of data model has one table, or file. Each line corresponds to some object (for example, a language), and each column represents a property (attribute), for example, the name, scope of use, or the preferred word order (for example, the order of the words Subject-Verb-Object is preferred for the United States sentence). >

2. A relational database consists of several tables (relations) of this kind, connected with each other in a certain way.

3. The hierarchical database is organized not in the form of a table, but in the form of a tree structure, similar to the structure of nested files on the computer's disk. Each data block belongs to a larger block and contains smaller units. A similar organization is adopted in books, divided into chapters, sections, then subsections, etc.

4. In an object-oriented database, data is modeled as objects of different types. Objects inherit properties depending on their type, for example, in the database of word classes, the objects of the class transitive verb inherit properties of the verb class.

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