Principle and Application of Database
Chapter One Introduction
1.1 Overview of the database system
Four concepts:
Data data: Symbol record describing things
Database DB: long-term storage in the computer, organized, shareable , large data collection, data model, small redundancy, high data independence, easy scalability
Database management system DBMS: DDL-data definition language, DML-data manipulation language
Database system DBS = database DB + DBMS (and application development tools) + application + DBA (administrator)
Store, manage, process and maintain data
three phases:
Manual management stage:
no independence; no structure; no sharing; great redundancy
File system stage:
poor independence; files have structure but no overall structure; poor sharing and high redundancy
Database system stage:
data structured (essentially different from file system)
high sharing, low redundancy and easy to expand,
high data independence (physical independence, logical independence)
data is managed and controlled by the database management system
①safe protection
② integrity check
③ concurrency control
④ database recovery
1.2 Data model (the core and foundation of the DBS database system)
Data model is an abstraction of real world data characteristics
Two types of data models:
Conceptual model (information model): entity-connection method (E-R method)
Logical model and physical model: The
physical model is not too much to introduce. Logical models include hierarchical, mesh, and relational models. The hierarchy and mesh are formatting models
Picture slightly (computer illustration is too tossing people)
Elements of the data model:
Data structure, data operation, data integrity constraints
1.3 The structure of the database system
Three-level model structure of DBS: outer model, model, and inner model
concept
Mode (logical mode) is a description of the logical structure and characteristics of all data in the DB, and is a common data view for all users
External mode (sub mode or user mode): description of the logical structure and characteristics of local data
Internal mode (storage mode): A DB has only one internal mode , which is a description of the physical structure and storage of data
Secondary image and data independence
External mode/mode image
A mode change mode allows external data → constant logic independent of
Mode/intra mode image
When the DB storage structure changes, so that the same pattern → physically independent of
1.4 The composition of the database system
DBS=DB+DBMS+DBA+application
DBA work:
1. Determine the content and structure of the information in the DB.
2. Determine the storage structure and access strategy of the DB.
3. Define the security requirements and integrity constraints of the data.
4. Monitor the use and operation of the
database. 5. Improve and improve the database. Reorganization, reconstruction
As a simple version of the notes, the content is summarized by the author himself. It is inevitable that there are omissions and incomplete places. Please forgive me!
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