Database Fundamentals-Database System Overview

four basic concepts of a database

1. Data: A description of the record symbol of a thing, video, audio, Chinese characters, graphics is a form of data.
2. Database: A data warehouse that organizes, stores, and manages data that is stored on a computer's storage device. Strictly speaking, the database refers to the long-term storage in the computer, organized, shareable data collection. The data in the database is organized, described and stored by a certain data model, which has small redundancy, high data independence and expansibility, and is shared by various users.
3. Database management system: is the data management software between user and operating system, including data definition function, data organization, storage and management function, data manipulation function, database transaction management and operation management, database establishment and maintenance, other functions, such as communication, data conversion.
4. Database system: A system consisting of databases, database management systems (and their application development tools), applications, and database administrators that store, manage, process, and maintain data. Left is the internal structure diagram of the database management system, and right is the computer hierarchy diagram after the introduction of the database

characteristics of the database system

• Structure of the data

the structure of the data is not for an application, but for all organizations, not only the internal structure of the data, the overall structure, the data are linked. For example, a student selection system, need to include department information and academic Office information, not only student information and student information

• The sharing of data

Data within a database can be shared by multiple users and applications, reducing data redundancy, saving space, and avoiding data inconsistencies and incompatibilities.

• The independence of the data

The independence of data is divided into physical independence and logical independence.

Physical independence means that the user's application is independent of the physical storage of the database. The data of the database is determined by the DBA to determine the storage policy and storage details and so on, the user does not need to know;

Logical independence refers to the user's application and the logical structure of the database is independent of each other, the structure of the database changes the user's application does not need to change.

• Data database management system management and control

Data sharing-database data can be accessed by multiple users at the same time, or even access the same data.

Data security protection-protect data against unsafe disclosure and destruction of data.

Data my integrity check-ensure the correctness, validity and compatibility of the data. Make the data in the right range, and ensure that there is a certain connection between the data.

Concurrency control-The simultaneous operation of multiple users needs to be controlled to avoid errors.

Database recovery-Data hardware, software, data administrators, and vandalism can cause data errors, and database management software needs to provide recovery to restore data from the wrong state to the correct state.

use a wide range of databases now

Now the mainstream database software in the market is: Oracle,db2,sql server,mysql,sybase.

Oracle

In 1977, Oracle's founder created Oracle with the relational data theory to enable basic query functionality for the database.

Oracle is a relational database management system, a system that organizes data into related rows and columns, other relational data management systems, and SQL Server.

Oracle database is the most widely used database management system in the world, as a general database system, it has complete data management function, as a relational database, it is a complete relational product; As a distributed database, it realizes the distributed processing function.

Many of the enterprise's online transaction processing systems, internal financial systems, customer management systems and other large data volume systems are mostly Oracle-based.

Db2

IBM DB2 is a relational database management system developed by IBM in the United States, and its main operating environment is UNIX (including IBM's own Aix), Linux, IBM i (formerly known as os/400), z/OS, and the Windows Server version.

DB2 is mainly used in large-scale applications, with good scalability and support from mainframe to single-user environments, to all common server operating system platforms.

DB2 provides high-level data utilization, integrity, security, recoverability, and execution capabilities for small to large-scale applications, with basic platform-agnostic functionality and SQL commands.

The DB2 employs data classification technology to enable mainframe data to be easily downloaded to a LAN database server, enabling client/server users and LAN-based applications to access mainframe data and make database localization and remote connectivity transparent.

DB2 is known for having a very complete query optimizer, whose external connections improve query performance and support multitasking parallel queries.

DB2 has a good network support capability, each subsystem can connect a hundred thousand of distributed users, can activate thousands of active threads at the same time, especially for large distributed application system.

Oracle vs. DB2 use comparison: DB2 and Oracle Impressions compare http://www.itpub.net/thread-1265829-1-1.html (Source: Itpub Forum-The most professional IT technology community in China

SQL Server

SQL Server is a relational database management system launched by Microsoft Corporation. Originally developed jointly by Microsoft, Sybase and ashton-tate three companies, it was launched in 1988 with the first OS/2 release. After the launch of Windows NT, Microsoft and Sybase split up on SQL Server development, and Microsoft migrated SQL Server to the Windows NT system, focusing on developing windows for promoting SQL Server NT version, which becomes MS SQL Server. Sybase is more focused on SQL Server applications on the Unⅸ operating system.

MS SQL Server is primarily for SMBs. Its biggest advantage is the integration of MS Company's various products and resources, provide a powerful visual interface, highly integrated management development tools, in small and medium-sized enterprises can achieve rapid development.

MySQLMysq L is a relational data management system developed by the Swedish MySQL AB company and is currently part of Oracle's product portfolio. While MySQL offers less functionality than large software such as Oracle, MySQL provides more than enough functionality for general personal users and small and midsize businesses, and because MYSQ L is open source software, it can significantly reduce total cost of ownership. MySQL often develops free systems with a combination of PHP, Python, and Perl software. SybaseA relational database system developed by Sybase, a typical UNIX or WindowsNT platform, is a large database system in a client/server environment. Database, although no Oracle, DB2 fame, but many large enterprises in the domestic use it, especially financial enterprises.

Database Fundamentals-Database System Overview