Database system learning and foundation compaction--basic knowledge (II.)

Database architecture

Understanding the entire structure of the database, can help us to learn further.

Today we use the mainstream database system (such as MSSQLServer), basically the ANSI/SPARC system and structure: including internal mode, conceptual mode and external mode three layer.

Internal Mode-storage mode, the physical storage method of data;

External mode-user mode, the user can actually see the view of the data;

Conceptual mode-public logic mode, which is the middle layer of the first two modes.

From, it can also be seen that for the external model (as for a single user) there will be more than one, and they only have a "conceptual view" (conceptual mode), can be analogous to a

The company database can correspond to multiple users. Further down, the data storage view (internal mode) also corresponds to only one, which is used to represent the physical storage of the data.

In a relational system, there are several key points to understanding the three-level architecture:

First, the conceptual pattern of a relational system is a matter of relation, and this layer of visible entities is the operator of the relationship's table and relationship;

Second, the external view is also relational or close to the relationship;

Thirdly, the internal mode is not the relationship, it is not the same as the copy of the relational table, even if the system is actually the same model (pointers, indexes, hash tables, etc.);

System Architecture Diagram:

　　

Other important concepts

Database administrator (DBA): A person who formulates policies and policy decisions based on the data of the enterprise.

Database management System (DBMS): It is the software that handles database access.

Generally there should be a process,

1) A user may use a data language (SQL) to make an access request;

2) The DBMS accepts requests for access and makes analysis;

3) The DBMS then checks the user's external mode, corresponding to the mapping of the external mode/concept mode, the conceptual mode, the concept mode/internal schema mapping and the storage structure definition;

4) The DBMS performs the necessary operations on the database.

At least some features can be supported,

1) data definition, support various data definition language (DDL), such as creating database, creating table, etc.;

2) Data manipulation, data in the database can be modified and deleted, including the database Manipulation language (DML) support;

3) Also, DML should be "planned" (Request execution can anticipate its related requirements) or "unplanned" (unpredictable before execution of requests, i.e. special queries);

4) optimization and execution, the manipulation of language requests must be handled by the optimizer (SQL Server optimizer), which determines

5) Data security and integrity, real-time monitoring of user requests, and can deny the DBA to define database security and integrity constraints disruptive operations;

6) Data recovery and concurrency, transaction manager (monitor);

7) The data dictionary, which itself can also be regarded as a database (that is, the system database), it is called "Data data".

This article refers to the introduction of database System (7th edition)

PS: Tiandaochouqin, willing to share with everyone, through the blog to stimulate learning, do not like to spray 0.0, hope that the future better more original content.

Database system learning and foundation compaction--basic knowledge (II.)