Database management System

Today summed up the "database", drew two pictures, below according to my diagram, say the knowledge of learning.

Figure 1

Figure 2

1, the database life cycle is divided into three major stages: planning, design, implementation, the three are layers of progressive relationship. Then a detailed description is made from three aspects.

First, the planning stage is mainly to explain the software is "what", according to user needs to produce a conceptual model, the most image of the method is the use of ER model, that is, the entity contact model.

Then say the design phase, this phase is mainly divided into logical design and physical design, of course, also related to the development environment, here are two kinds: Power builder and SQL sever2000, we have used SQL sever2008, this book is obviously "too old". Logical design produces a logical model, which should appear after the selected DBMS software in Figure 2, and relies primarily on software, which has three classifications, hierarchies, meshes, and relational models (two-dimensional tables). We are now most used in the relationship model, the relationship model contains a number of relational patterns, the purpose of the logical design is to transform the conceptual design phase design of the conceptual model to the selected machine based on the data model supported by the DBMS to conform to the logical structure, here is to convert the ER model to relational mode. Define the language of the relational schema we can choose the SQL language. Physical design produces physical structure, that is, the database storage record format, storage record arrangement and access method, different from the logical design, it is completely dependent on the hardware.

The last is the implementation of the database. Database design should start to use, then you should compile and debug the corresponding application, and then carry out a small part of the data storage, start the database trial run. It is mainly for performance and function debugging. Of course, maintenance is essential. The security of the data we should all consider.

Below 2, the big role of Figure 2 is DBS (database system), which includes DBA (database administrator), DBMS (software), DB (Database). The application uses the DBMS to reach the data in db, and then the DB passes the query results back to the application through the DBMS. The DBMS contains the DDL compiler (defining level three of the database), the DML compiler or interpreter (add, delete, change, check), and the data dictionary-dd that holds the three-level structure definition. The DBMS monitors the DBS when it is running. The minimum logical unit of a DBS run is "transactions", and operations on the database are performed or revoked in the transaction unit. The DBA uses some of the programs in the DBMS and the DD system to master the work of the entire DBS. So the responsibility of the DBA is rather heavy and requires a high level of seniority.

This is my understanding of the book, the shortcomings of the more advice please!

Database management System