光阴冢 赛博空间的自留地

DBS - File-based System

Limitations of File-based System

  • Separation and isolation of data

  • Duplication of data

  • Data dependence

  • Incompatible file formats

  • Fixed queries/proliferation of application programs

Database Approach

  • The description of the data is known as the system catalog (or data dictionary or metadata – the ‘data about data’). It is the self-describing nature of a database that provides program–data independence.

  • Organize

    1. An entity is a distinct object (a person, place, thing, concept, or event) in the organization that is to be represented in the database.

    2. An attribute is a property that describes some aspect of the object that we wish to record.

    3. A relation-ship is an association between entities.

DBMS

Software.

Facilities

  • Data Definition Language (DDL), to define the database, to specify the data types and structures and the constraints.

  • Data Manipulation Language (DML), to insert, update, delete, and retrieve data. Structured Query Language (SQL), formal and standard.

  • Controlled Access

  • Views

    View mechanism.

    1. Provide a level of security.

    2. Provide a mechanism to customize the appearance of the database.

    3. Present a consistent, unchanging picture of the structure of the database.

Little Points

  • The structure of the database is called the schema.

  • The constraints are sometimes called business rules.