วันจันทร์ที่ 4 พฤศจิกายน พ.ศ. 2556

■Database component


A database management system (DBMS) consists of several components. Each component plays very important role in the database management system environment. The major components of database management system are:

  • Software
  • Hardware
  • Data
  • Procedures
  • Database Access Language
Software
The main component of a DBMS is the software. It is the set of programs used to handle the database and to control and manage the overall computerized database

Hardware
Hardware consists of a set of physical electronic devices such as computers (together with associated I/O devices like disk drives), storage devices, I/O channels, electromechanical devices that make interface between computers and the real world systems etc, and so on. It is impossible to implement the DBMS without the hardware devices, In a network, a powerful computer with high data processing speed and a storage device with large storage capacity is required as database server.

Data 
Data is the most important component of the DBMS. The main purpose of DBMS is to process the data. In DBMS, databases are defined, constructed and then data is stored, updated and retrieved to and from the databases. The database contains both the actual (or operational) data and the metadata (data about data or description about data).

Procedures
Procedures refer to the instructions and rules that help to design the database and to use the DBMS. The users that operate and manage the DBMS require documented procedures on hot use or run the database management system. These may include. Procedure to install the new DBMS.

Database Access Language
The database access language is used to access the data to and from the database. The users use the database access language to enter new data, change the existing data in database and to retrieve required data from databases. The user write a set of appropriate commands in a database access language and submits these to the DBMS. The DBMS translates the user commands and sends it to a specific part of the DBMS called the Database Jet Engine. The database engine generates a set of results according to the commands submitted by user, converts these into a user readable form called an Inquiry Report and then displays them on the screen. The administrators may also use the database access language to create and maintain the databases.The most popular database access language is SQL (Structured Query Language). Relational databases are required to have a database query language.

Users
The users are the people who manage the databases and perform different operations on the databases in the database system.There are three kinds of people who play different roles in database system

    ■Database


    A database is an organized collection of data. The data are typically organized to model relevant aspects of reality in a way that supports processes requiring this information. For example, modeling the availability of rooms in hotels in a way that supports finding a hotel with vacancies.Database management systems (DBMSs) are specially designed applications that interact with the user, other applications, and the database itself to capture and analyze data. A general-purpose database management system (DBMS) is a software system designed to allow the definition, creation, querying, update, and administration of databases. Well-known DBMSs include MySQL, PostgreSQL, SQLite, Microsoft SQL Server,Oracle, SAP, dBASE, FoxPro, IBM DB2, LibreOffice Base and FoleMaker Pro. A database is not generally portable across different DBMS, but different DBMSs can interoperate by using standard such asSQL and ODBG or JDBC to allow a single application to work with more than one database.


    ■Data type


    ข้อมูลสามารถแบ่งได้หลายลักษณะขึ้นกับว่าจะใช้เกณฑ์ใดในการแบ่ง เช่น
    1.ข้อมูลปฐมภูมิ ( Primary Data)คือข้อเท็จจริงหรือรายละเอียดที่ผู้เก็บข้อมูลลงมือเก็บด้วยตนเองได้มา จากแหล่งกำเนิดที่แท้จริง เช่น ข้อมูลจากการสัมภาษณ์ การสังเกต การทดลอง การทดสอบหรือการวัดจากกลุ่มตัวอย่างโดยตรง
    2.ข้อมูลทุติยภูมิ (Secondary Data) คือข้อเท็จจริง หรือรายละเอียดที่ผู้อื่นรวบรวมไว้อย่างเป็นระบบ สามารถนำมาเป็นข้อมูล โดยไม่ต้องลงมือเก็บรวบรวมเอง เช่น ข้อมูลจากระเบียนสะสม รายงานประจำปี สารานุกรม เอกสารเผยแพร่ เป็นต้น