Structure and Composition of Database System

1.3 Structure of the database system

• From the perspective of database application developers,
  the database system adopts a three-level schema structure, which is the internal system structure of the database system.
• From the perspective of the database end user,
  the structure of the database system is as follows:
  • single user structure
  • master-slave structure
  • distributed structure
  • client-server architecture
  • Browser - application server/database server etc.

1. The concept of database system schema

model

• It is a description of the logical structure and characteristics of the database
• Is a type description, does not refer to specific values
• mode is relatively stable

example

• The state of the database at a certain moment - a concrete value of the schema
• There can be many instances of the same pattern
• The instance changes as the data in the database is updated

1. Mode

2. External mode

3. Internal mode

Second, the secondary image function and data independence of the database

1. External mode/mode image

2. Mode/internal mode image

• Ensures the stability of the application
• Applications generally do not require modification unless the application requirements themselves change
• From program-centric to data-centric
• With the independence between data and program, the definition and description of data can be separated from the application program
• Data access is managed by a database management system
• Simplifies application programming
• Significantly reduces application maintenance and modification

1.4 Composition of the database system

1. Hardware platform and database

• Database system requirements for hardware resources
• enough memory
• Sufficiently large external devices such as disks or disk arrays
• Higher channel capacity, increased data transfer rate

2. Software

• database management system
• The operating system that supports the operation of the database management system
• A high-level language machine compilation system for interfacing with databases
• Application development tools with database management system as the core
• A database application system developed for a specific application environment

3. Personnel

chapter summary

focus:

• Firmly grasp the basic concepts of the conceptual model; the three components of the data model;
• The architecture of the three-level schema and the two-level image of the database system;
• Logical independence and physical independence of the database system, etc.

difficulty:

• basic concept
• Data Model and Architecture of Database System