Definition: the symbol records of a transaction can be described (and record computer indicating a format or a method of storing data) referred to as data.

Data are stored in the database of the base object .

Everything data, it can be text, graphics, images, audio, video and so on.

※: data needs semantics (meaning data) auxiliary, and semantic data are inseparable

Example: 93 this data, simply stored in the computer, we do not know what it means, it is 93 yuan, or 93 pounds, or 93 centimeters, have their own data semantics, meaning that we can know the exact data.

Database (DataBase, DB)

Database, suggests that it is storing data warehouse. It is a long-term storage in the computer, organized (in favor of access), it can be shared by a large number of data collection .

Data in the database by some model data organization, storage and described , having less redundancy , higher data independence and easy to extend , for a variety of users can share .

In summary, the database has a permanent memory, organized and shared three basic characteristics.

Database management system (DataBase Management System, DBMS)

Database management system is located between the user and the operating system layer of data management software , and operating system software as the basis for the computer.

It can organize and store scientific data and efficient access to and maintenance data.

The main function of the database management system include the following aspects:

1, data definition function:

Composition and structure of data objects defined in the database (want to manage must first define)

2, data organization, storage and management:

Categories organize, store and manage data

Storage file structure and the data determined

Realize the link between data

It provides a method of accessing data

3, data manipulation functions

Basic operation of the database: Charles change deletions

4, things management and operational management of the database

In establishing a database, use and maintenance of the unified management and control by the database management system to ensure proper operation of the transaction to ensure data security, integrity, multi-user concurrent use of data and system recovery after a failure.

5, database creation and maintenance functions

Database system (DataBase System, DBS)

Database system consists of database, database management systems, application and database administrators composed store, manage, and maintain data processing system

Without confusion, people often referred to as the database system database

And development of data management technology (to understand)

Features Database System

1, structured data

This is the database system ( as a whole structured ) and file systems (internal structure) of the essential difference

The so-called "whole" refers to structured data in the database is no longer just for certain applications, but for the entire organization or enterprise; not only the internal data is structured, but overall is structured, there are links between data .

2, data sharing is high, low redundancy and easy expansion

Data for the entire system, may be a plurality of users, a plurality of applications using shared ( shared cause low redundancy ), the data structured easy to add new applications (elasticity, easy to expand ).

3, high data independence

Database system comprising: a high degree of independence and physical independence of a certain logic .

Refers to the physical independence of the user's applications and the physical storage of data in the database are independent of each other, when the physical storage changed without changing the application data.

Independence logic refers to a logical structure of the user applications and databases are independent of each other, when the user changes the logical structure of the program data may be constant.

4, unified management and control of data by the database management system

Database must provide the following data control functions: recover data security, data integrity, concurrency control, the database

Data Model

Data model is also a model, he is an abstraction of the real world data features, which means that the data model is used to describe data, organizational data and data operations. In layman's terms, data models is to simulate the real world, the real world is digitized to the computer to see .

The data model is the core and foundation of database systems, implemented on a variety of machines database management system software is based on a data model or data model to support some kind.

Constituent elements of the data model

Data model from the data structure, data manipulation and data integrity constraints of three parts.

Collection object data structure is of the type described, the system is static character described.

Operating system data is dynamic character described.

Data integrity constraint is a set of integrity rules to define changes in the database and a state consistent with the data model, to ensure that the data is correct, effective and compatible.

Depending on the purpose of application of the model, the model is divided into two categories: conceptual model and logical model

Conceptual Model

According to the user point of view of data and information modeling, mainly for database design, it is on posters .

The concept model is actually the real world to a middle-level machine in the world, it should have a strong semantic expression, can be easily and directly express various semantic knowledge applications, it should be simple, clear and easy to understand.

Representation: entity - Contact (ER diagram)

Logic Model

Press the point of view of the computer system for data modeling, mainly used to implement database management system, is to look at the computer .

It comprises a hierarchical model, a mesh model, the relational model, the data model object-oriented and object-relational data model, semi-structured model.

Hierarchical Model

Hierarchical model is a data model for database systems first appeared, it is a typical representative of IBM's IMS (Information Management System).

Level model with a tree structure to represent the links between the various types of entities and entities.

1, hierarchical model data structures ( one to one, one to many )

There is only one no parent node, the other node has one and only one parent node

2, data manipulation and hierarchical model integrity constraints

Conventional CRUD, but to satisfy the integrity constraints: when inserted, the absence of the corresponding parent node values can not be inserted to its child node value; delete, delete the parent node if the value of the corresponding child node value It will be deleted.

Network Model

Mesh model is representative of a typical system DBTG

1, the mesh model data structure ( to-many, many-staggered like mesh )

Allow no more than one parent node, a node can have more than one parent (no parent or parents support).

2, and the mesh model of the operation of the data integrity constraints

The network database system specific data operations are added to some restrictions, integrity constraints provide a

Relational Model

First introduced the relational model some of the terms:

Relationship: a relationship is a table

Tuple: a table row that is a tuple

Properties: table has a column that is a property

Code: can uniquely identify a tuple of the minimum set of attributes (student number in the following table may uniquely identify a student, it can be a code)

Domain: a set of values having the same type of data collection

Component: a tuple attribute value

Relational schema: description of the relationship - the relationship name (attribute 1, attribute 2, ....., attribute n) [student (Student ID, name, sex ....)]

There are relational model does not allow the table table, i.e., each component must be a data item inseparable

1, the data structure of the relational model: a two-dimensional table shown in FIG. 1.14

2, the relationship between model and data manipulation integrity constraints

Data manipulation including query, insert, delete, and update data. The operation of the relational model is a collection operation, operation and operating results are subject relationship.

Integrity constraints include three categories: physical integrity, referential integrity integrity and user-defined

Structure of the database system

From the perspective of database application development, database systems typically employ three model structure, which is a database system of the internal system configuration.

End-user from the database point of view, the structure of the user database system into a single structure, from the main structure, distributed architecture, the client - server, browsers - the application server / database server multilayer structure, which is a database system, the external system structure.

The concept of a database system mode

Data model of "type" and the concept of "value", simply, "type" is a class, and "value" is the object. Type is a structure and properties of a class of data, a specific value is assigned type.

A data schema is a description of all features and logical structure database, type only relates to the description, specific design values are not. Same pattern can have many specific value (called an instance).

Database systems often employ three mode configuration and provides two mapping function.

Three mode structure of the database

Pattern is common to all users view. A database is only a model, not only to define the logical structure of the data defining mode (data recording what constitutes a data item name, type, range, etc. of) links between, but also to define data definitions and data security-related , integrity requirements.

External mode , also known as user mode, the user is to look at the data and uses the logical structure and local features described. Popular that is external to the user with the pattern end, end users, and other business end, a program can have multiple end, i.e. a database can have multiple external modes. Outside the protection of the database model is a measure of security, but also to ensure the independence of the data logic, different external data models can open different permissions (allow cross).

The mode is also called storage mode, and is described in the physical structure of data storage, a database can only be made within a pattern.

The mode: Mode: external mode: Application = 1: 1: Multi: Multi

Two image database functions and data independence

Between the three modes, the database management system provides two images: an outer mode / image mode and a mode / the mode map

1, the outer pattern / mode map

Mode describes the logical structure data of the global, local mode describes the outer logical structure data. External mode / mode map defines the correspondence between the mode and the external mode. When the mode change (adding a new relation, attribute, change the properties and the like), an image for a corresponding change in the respective outer pattern / mode by the database administrator, the outer pattern remains unchanged, so that the application program need not be changed to ensure that the data logical independence of the program, referred to as logical data independence.

2, the mode / the mode map

This is the only image, defines the correspondence between the logical structure and the global data storage structure. When the storage structure of the database changed (changing the storage structure), by the database administrator mode / work mode map corresponding to the changes, so that mode remains unchanged, so that the application program need not be changed to ensure that the physical independence of the data and programs , referred to as the physical data independence.

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(A) Introduction to the basic concepts of database systems, stage of development

4 basic database concepts

Data (data)