Welcome to my “Characteristics of database management system.”
The basic characteristics of the database are.
1. The basic characteristics of the database are.
A. (1) data can be shared (or data structure) (2) data independence
(3) data redundancy, easy to transplant (4) unified management and control
B. (1) data can be shared (or data structure) (2) data independence
(3) small data redundancy, easy to expand (4) unified management and control
C. (1) data can be shared (or data structure) (2) data interchangeability
(3) small data redundancy, easy to expand (4) unified management and control
D. (1) data unstructured (2) data independence
(3) small data redundancy, easy to expand (4) unified management and control
1. The basic characteristics of the database are.
A. (1) data can be shared (or data structure) (2) data independence
(3) data redundancy, easy to transplant (4) unified management and control
B. (1) data can be shared (or data structure) (2) data independence
(3) small data redundancy, easy to expand (4) unified management and control
C. (1) data can be shared (or data structure) (2) data interchangeability
(3) small data redundancy, easy to expand (4) unified management and control
D. (1) data unstructured (2) data independence
(3) small data redundancy, easy to expand (4) unified management and control
Data Structured Data has a relationship between, for the entire system. 2. Data sharing, low redundancy, easy to expand 3. High data independence 4. Data by the DBMS unified management and control
(A) data can be shared, data independence, data redundancy, easy to transplant, unified management, and control
(B) Data can be shared, data independence, data redundancy is small, easy to expand, unified management and control
(C) data can not be shared, data interchangeability, data redundancy is small, easy to expand, unified management and control
(D) Unstructured data, data independence, large data redundancy, easy expansion, unified management, and control.
(A) data can be shared, data independence, data redundancy, easy to transplant, unified management, and control
(B) Data can be shared, data independence, data redundancy is small, easy to expand, unified management and control
(C) data can not be shared, data interchangeability, data redundancy is small, easy to expand, unified management and control
(D) Unstructured data, data independence, large data redundancy, easy expansion, unified management, and control.
Data structure
The data structure is the fundamental difference between the database and the file system. In the file system, records of mutually independent files are structured internally. The simplest form of a traditional file is a record set of the same length and the same format. For example a student's personnel records, each record has the record format shown in Figure 1.
2. Data sharing, low redundancy, easy to expand
Database system describes the data from an overall perspective, the data is no longer for an application but for the entire system, so the data can be shared by multiple users, multiple applications. Data sharing can greatly reduce data redundancy and save storage space. Data sharing also avoids data inconsistencies and inconsistencies. The so-called data inconsistency refers to the same data different copies of the value is not the same. When using manual management or file system management, because the data is repeatedly stored, data inconsistencies can easily result when different applications use and modify different copies. Data sharing in the database reduces inconsistencies caused by data redundancy. As the data for the entire system is structured data, not only can be shared by multiple applications but also easy to add new applications, which makes the database system flexible and easy to expand, you can adapt to various user requirements. Can take a variety of subset of the data in different application systems, when the application requirements change or increase, as long as the re-select a different subset or add some of the data to meet new needs.
3 data independence
The independence of data is a common term in the database domain, including the physical independence of data and the logical independence of data. Physical independence means that the user's application and the data stored in the database on the disk are independent of each other. That is, data is stored in the database on the disk by the DBMS, and the user program does not need to know that the application processes only the logical structure of the data so that when the physical storage of the data changes and the application does not change. Logical independence refers to the logical structure of the user's application and the database is independent, that is, the logical structure of the data changes, the user program cannot change. Data and program independence, the definition of data separated from the program, coupled with the data access by the DBMS is responsible for simplifying the preparation of the application, greatly reducing the maintenance and modification of the application.
4. The data is managed and controlled by the DBMS
Database sharing is concurrent sharing, that is, multiple users can access the data in the database at the same time, and can even access the same data in the database at the same time. To this end, DBMS must also provide the following data control functions:
(1) data security (Security) protection
Data security refers to the protection of data to prevent data leakage and destruction caused by illegal use. So that each user can only according to the provisions of some of the data in some ways to use and processing.
(2) Integrity check of the data
Data integrity refers to the correctness, validity, and compatibility of the data. Integrity checks to control the data within the effective range, or to ensure that the data to meet a certain relationship.
(3) Concurrency control
When multiple users simultaneously access concurrent processes, modify the database may interfere with each other to get the wrong results, or the integrity of the database has been destroyed, it must be the multi-user concurrent operation to be controlled and coordinated.
(4) database recovery (Recovery)
Computer system hardware failure, software failure, operator error, and intentional damage will affect the correctness of the data in the database, and even cause some or all of the database data loss. The DBMS must have the ability to recover the database from the error state to a known, correct state (also known as full state or consistent state), which is the database recovery feature. Database management phase Application and the correspondence between the database can be used as shown in Figure 1-3 structure. See the book. Databases are long-term, organized, massively shared data sets stored in computers. It can be shared by a variety of users, with minimal redundancy and high data independence. DBMS database in the establishment, use and maintenance of unified control of the database in order to ensure data integrity, security, and multi-user concurrent use of the database for concurrent control in the event of a failure to recover the system. The advent of database systems has transformed information systems from a process that processes data to a new phase that centers around shared databases. This not only facilitates the centralized management of data but also facilitates the development and maintenance of application programs, improves the utilization and compatibility of data, and improves the reliability of decision-making. At present, the database has become an inseparable part of the modern information system. Databases with millions or even billions of bytes of information are common in information systems in science and technology, industry, agriculture, commerce, services, and government.
The data structure is the fundamental difference between the database and the file system. In the file system, records of mutually independent files are structured internally. The simplest form of a traditional file is a record set of the same length and the same format. For example a student's personnel records, each record has the record format shown in Figure 1.
2. Data sharing, low redundancy, easy to expand
Database system describes the data from an overall perspective, the data is no longer for an application but for the entire system, so the data can be shared by multiple users, multiple applications. Data sharing can greatly reduce data redundancy and save storage space. Data sharing also avoids data inconsistencies and inconsistencies. The so-called data inconsistency refers to the same data different copies of the value is not the same. When using manual management or file system management, because the data is repeatedly stored, data inconsistencies can easily result when different applications use and modify different copies. Data sharing in the database reduces inconsistencies caused by data redundancy. As the data for the entire system is structured data, not only can be shared by multiple applications but also easy to add new applications, which makes the database system flexible and easy to expand, you can adapt to various user requirements. Can take a variety of subset of the data in different application systems, when the application requirements change or increase, as long as the re-select a different subset or add some of the data to meet new needs.
3 data independence
The independence of data is a common term in the database domain, including the physical independence of data and the logical independence of data. Physical independence means that the user's application and the data stored in the database on the disk are independent of each other. That is, data is stored in the database on the disk by the DBMS, and the user program does not need to know that the application processes only the logical structure of the data so that when the physical storage of the data changes and the application does not change. Logical independence refers to the logical structure of the user's application and the database is independent, that is, the logical structure of the data changes, the user program cannot change. Data and program independence, the definition of data separated from the program, coupled with the data access by the DBMS is responsible for simplifying the preparation of the application, greatly reducing the maintenance and modification of the application.
4. The data is managed and controlled by the DBMS
Database sharing is concurrent sharing, that is, multiple users can access the data in the database at the same time, and can even access the same data in the database at the same time. To this end, DBMS must also provide the following data control functions:
(1) data security (Security) protection
Data security refers to the protection of data to prevent data leakage and destruction caused by illegal use. So that each user can only according to the provisions of some of the data in some ways to use and processing.
(2) Integrity check of the data
Data integrity refers to the correctness, validity, and compatibility of the data. Integrity checks to control the data within the effective range, or to ensure that the data to meet a certain relationship.
(3) Concurrency control
When multiple users simultaneously access concurrent processes, modify the database may interfere with each other to get the wrong results, or the integrity of the database has been destroyed, it must be the multi-user concurrent operation to be controlled and coordinated.
(4) database recovery (Recovery)
Computer system hardware failure, software failure, operator error, and intentional damage will affect the correctness of the data in the database, and even cause some or all of the database data loss. The DBMS must have the ability to recover the database from the error state to a known, correct state (also known as full state or consistent state), which is the database recovery feature. Database management phase Application and the correspondence between the database can be used as shown in Figure 1-3 structure. See the book. Databases are long-term, organized, massively shared data sets stored in computers. It can be shared by a variety of users, with minimal redundancy and high data independence. DBMS database in the establishment, use and maintenance of unified control of the database in order to ensure data integrity, security, and multi-user concurrent use of the database for concurrent control in the event of a failure to recover the system. The advent of database systems has transformed information systems from a process that processes data to a new phase that centers around shared databases. This not only facilitates the centralized management of data but also facilitates the development and maintenance of application programs, improves the utilization and compatibility of data, and improves the reliability of decision-making. At present, the database has become an inseparable part of the modern information system. Databases with millions or even billions of bytes of information are common in information systems in science and technology, industry, agriculture, commerce, services, and government.
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