Delphi Development Database Application Overview

13.1 Database System Overview

The database system provides us with a way to bring together information that is closely related to our work and life, and it also provides a way to store and maintain this information in a centralized location. The database system is mainly composed of three major parts: Database management System (DBMS: A program that specializes in organizing and managing data information), database applications (which enable us to acquire, display, and update data stored by the DBMS), a database (a collection of related data grouped together by a certain structure).

In general, DBMS and database applications reside on the same computer and run on the same computer, in many cases even in the same program, and most database systems used previously were designed in this way. However, with the development of DBMS technology, the current database system is developing to the client/server model. The client/server database separates the DBMS from the database application, which improves the processing power of the database system. The database application runs on one or more user workstations (clients) and communicates over the network with one or more DBMS running on another computer (the server).

The following are some concepts and references in the database system.

13.1.1 Database management System (DBMS)

Database management System (DBMS) is a program system which is used to describe, manage and maintain database, and is the core component of database system. It is based on the operating system, unified management and control of the database. Its main functions are:

1. Description database: Describes the logical structure of the database, storage structure, semantic information and confidentiality requirements.

2. Management database: Control the operation of the entire database system, control the user's concurrent access, verify the data security, confidentiality and integrity, perform data retrieval, insert, delete, modify, and other operations.

3. Maintain the database: control the initial data loading of the database, log the work log, monitor the database performance, modify the update database, organize the database, restore the failed database.

4. Data communication: Organization of the transmission of information.

There are four main types of DBMS: File management system, hierarchical database system, network database system and relational database system. Because the current relational database system is most widely used, we focus on the introduction of several concepts in relational database system.

relational databases (relational database): A relational database is made up of several tables. In Delphi, the database concept corresponding to the physical file is somewhat different. For the three database systems of dBASE, FoxPro, and Paradox, the database corresponds to a subdirectory, while other types such as Ms Access and Btrieve refer to a file. This is because the table for the former is a separate file, and the table of the latter is clustered in a database file.

Table: A table is a set of related data arranged in rows, like a table. For example, a class of all students in the final exam results, there is a table, each line corresponds to a student, in this line, including the student's number, name and the results of each course.

Fields (field): In a table, each column is called a field. Each field has corresponding descriptive information, such as data type, data width, and so on.

Record: In a table, each row is called a record.

Index: To speed up access to a database, many databases use indexes.