First part
Seven, database system structure
1, mode (Schema): It is a description of the logical structure and characteristics of all data in the database, which only involves the description of the type, does not involve specific values.
2, three-level mode structure, as shown below:
3, logical mode: ie mode, is a description of the logical structure and characteristics of all data in the database, is a public data view of all users
4, external mode: Subschema, ie, user mode, is a description of the logical structure and feature of the database user to see and use, is a data view of the database user.
5, Internal Schema): Even if the storage schema, the data physical structure, and storage mode is a representation of data within the database.
6, Secondary Image: Ensure that the data in the database system can have high logical independence and physical independence.
1, external mode / mode image:
When the mode changes, the database administrator changes the image of each outer mode / mode, so that the external mode can remain unchanged, so that the application does not have to be modified to ensure logical independence of the data.
2, mode / internal mode image
When the storage structure of the database changes (eg, a more advanced storage structure) is used, the database administrator changes the pattern / internal mode image, which allows the mode to remain unchanged, thereby ensuring the physical independence of the data.
7. Database architecture:
1. Single user mode: The entire database system, including applications, dbms, data, all being installed on a computer, exclusive, unable to share data between different machines.
2, the database system of the main slave structure: refers to a multi-user structure with a host with multiple terminals. In this configuration, the database system, including applications, dbms, data, allocated on the host, all processing tasks are completed by the host, and each user uses the host's terminal to access the database to share data resources.
3. Database system of distributed structures: Database system of distributed structures refers to data in the database is logically a whole, but physically distributes on different nodes of computer networks. Each node in the network can independently handle data in the local database, perform local applications; simultaneous access and processing data in multiple off-site databases, and perform global applications.
4. Database System of Customer / Server Structure: Server: Computers on a (some) node in the network specifically used to perform DBMS functions, called database servers. Client: Computer installed on other nodes Install the peripheral application development tool to support users, called a client. Working Principle: In the client / server structure, the client's user request is transmitted to the database server. After the database server is performed, only the result is returned to the user (not the entire data).
8, the composition of the database system
1. Hardware: Sufficient memory and storage space; system should be higher channel capabilities
2, software: DBMS; supports DBMS OS; there is a high-level language with database interfaces and its compilation system 3, person: DBA, system analyst, database designer, application programmer, user.
Eight, database library technology research field
1, database theory
2, DBMS development
3, database design
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