Database system principle and design ~ Basic concept of contact (i) __ Database

One: What is a database. Database is a software system that organizes, stores and manages data according to certain data structure. (In simple terms, the management of the data is achieved) II: Classification of databases:Hierarchical database: A text structure similar to XML (HTML). Mesh Database:

Relational database:

Corresponding to three kinds of models: hierarchical model, mesh model, relational model.
The storage structure of the data is different. Next, we introduce the characteristics of three kinds of models, understand on the line, the unimportant hierarchical model: The earliest data model appearing in the database management system. Hierarchical database is the organization way of data by using hierarchical model
The following two-feature collection is a hierarchical model:

         * There is only one node that does not have a parent node, which is called the root section
         * root node, and the other node has only one parent node

The main advantages are:

        Data structure relatively simple
        and clear query efficiency
        provides good data integrity support

Main disadvantages:

        Query child node must be through parent node
        because of the tight structure, the hierarchy commands tend to be programmed.
        many links in the real world are not hierarchical (such as many-to-many connections), too idealistic

2. Mesh Model:
A set of basic hierarchical connections that meet the following two conditions is called a mesh model

        * Allow more than one node without parents
        * A node can have multiple parents

The main advantages are:

        <font size = "5" >* can more directly describe the real world
        * with good performance, high access efficiency </font>

The main disadvantages are:

        * Structure is more complex, and with the expansion of application scale, the structure of the database will become more and more complex, not conducive to the end user master
        

3. Relationship Model
The main advantages are:

Rigorous mathematical basis: relational algebra as a language model, relational data theory as the theoretical basis
of the concept of a single: whether the relationship between entities or entities are expressed in relation to the data (relationship) operations (query and update) results or relationships. So its data structure is simple, clear, user-friendly
access path transparent: With higher data independence, better security confidentiality, simplifying the programmer's work, improve the software development and maintenance efficiency

The main disadvantages are:

    Because the access path is transparent to the user, the query efficiency is often inferior to the non relational data model
    in order to improve the performance, the DBMS must query and optimize the user's query request, which increases the difficulty of the DBMS development.

What I'm talking about here is the relational model. Third: The mainstream database products:

Oracle, MS SQL Server, DB2, Sybase, Access, MySQL, etc. four: The nature and performance of database storage:

The essence is that a large number of "data values" through the database management system for a complex but logical structure of a clear and orderly storage
Performance: In fact, it is also some file storage.


Five: Common terminology in relational databases:

Data: A symbolic record describing things.
Database databases: A "logical name" for a specific stored data, usually a product (project/web site) that uses a database to store all of its data
Database management Systems Dbms:database Management system: usually refers to the database software products
Tables (datasheet) Table:
Fields field,
Column columns:
Line Row,
Record records: next in database system principle and Design ~ ~ Take MySQL as an example operation database (ii) talking about the operation of the database