Introduction to database system (Fifth Edition) notes Chapter 1 Introduction

1.1.1 Database 4 Basic concepts

1. data (Data) – The basic objects stored in the database

• Data and semantics are inseparable ( The same number in different contexts can have different meanings )

2. database (DataBase)

1. meaning

​ It's stored in a computer for a long time , organized 、 A collection of large amounts of data that can be shared

2. basic feature

• Data according to a certain Data model organization , Depiction and storage ;
• It can be shared by all kinds of users 、 Little redundancy 、 Easy to expand ;
• High data independence

3. Database management system (DataBase Management System)

• A layer of data management software located between the user and the operating system

• yes Basic software , One Large and complex software system

• Scientifically Organization and storage data 、 Efficiently Get and maintain data ( effect )

2. function

• Data definition function ,(DDL)
• Data organization 、 Storage and management
• Data manipulation function (DML) -- Add or delete check change
• Database transaction management and operation management
• Establishment and maintenance of database
• Other features ( signal communication , Data exchange )

4. Database system (DataBase)

1. meaning

• It refers to the system composition of introducing a database into a computer system .

2. constitute

• database
• Database management system
• Applications
• Database administrator

1.1.2 Data management

Classify the data , organization , code , Storage , Retrieval and maintenance

characteristic

• Data structure
• High data sharing 、 Low redundancy and easy expansion
• High data independence
  • High independence is guaranteed by the second impression function
• Data is managed and controlled by database management system

1.2 Data model

It's a simulation of the real world , Is the core and foundation of database system

classification

1. conceptual model
2. Logical model and physical model

Real world – abstract –> The information world – transformation –> Machine world ( Data model supported by database management system )

1.2.3 The components of the data model

• data structure : static characteristic
• Data manipulation : Dynamic characteristics
• Data integrity constraints : soul ( Use collocation semantics )

1.2.4 Common data models

1. Structured model
   1. hierarchical model
   2. Mesh model
2. relational model
3. Object oriented data model
4. Object relational data model
5. Semi structured data model

1. hierarchical model ( Trees -1 Yes n)

Conditions to be met :

• Only one root node
• Except for the root, other nodes have only one parent node

characteristic

• You cannot insert a node without parents
• Deleting parents will delete the child node in turn

advantage / shortcoming

• The structure is clear / High query efficiency
• It is impossible to express the relationship (n Yes n), There is no way to clearly indicate that a node has multiple parent nodes

2. Mesh model ( chart -n Yes n)

Under the condition that the hierarchical model is satisfied , Satisfactions

1. Allow more than one node to have no parents
2. A node can have multiple parents
3. The relationship is not unique , But you need to name each relationship

advantage / shortcoming

• Can be many to many , High storage efficiency
• Complicated structure , Not query friendly

3.* relational model

Conditions

• Every attribute is indivisible ( It is not allowed to have a table in the table ).– Satisfy the first paradigm

Integrity constraints

1. Entity integrity
2. Referential integrity
3. User defined integrity

advantage / shortcoming

1. Strictly based on mathematical concepts
2. A single concept , It is also related to data retrieval and update results ( surface )
3. The storage path is transparent to users , Higher data independence , Better security . It also simplifies the work of programmers and database development , But it also leads to low query efficiency ( You need to find your own path ).

1.3 The structure of the database system

1.3.1 Database system concept

• The pattern is relatively stable ( abstract class ), And the examples are relatively variable ( Entity class )
• Databases are typically Three level mode structure and two-level image function

1.3.2 Three level pattern structure of database system

1. Pattern
2. External mode
3. Internal mode

1. Pattern

1. Also known as logical mode
2. The logical structure of all data , Is a common data view for all users
3. A database has only one schema

2. External mode

1. Also known as Subscheme Or user mode
2. Description of logical structure and characteristics of local data
3. A database can have multiple external schemas
4. An application has only one external mode , But one external mode can be used by multiple applications ( One person looks at a window , But one window can show many people )
5. It is a powerful measure to ensure database security

3. Internal mode

1. Also known as storage mode
2. Description of data physical structure and storage method
3. A database has only one internal schema

1.3.3 Secondary image function and data independence

1. External mode / Pattern image

1. A pattern can have multiple external patterns , But an external mode can only have and only have one external mode / Pattern image
2. If the mode changes ---- Modify each external mode / Pattern impression ----> You can keep the outer mode unchanged –> Application does not need to be modified . This is logical independence

2. Pattern / Internal mode image

1. The database has only one schema , And there is only one inner mode . So the pattern / Intrinsic mode image unique
2. If the storage structure of the database changes ---- Modify mode / Internal mode image ----> Leave the pattern unchanged , From the outside / Application does not need to be modified , This is physical independence

repair : Overall diagram of mode

1.4 Composition of database system

1.4.3 Database administrator

• Determine the content and structure of the information in the database
• Storage structure and access policy
• Safety requirements and integrity constraints ( Secure storage )
• Monitor the use and operation of the database ( Backup , Prevent invasion )
• Database improvement and reorganization , restructure ( Performance monitoring )