Limitations of File-based System
- Separation and isolation of data
- Duplication of data
- Data dependence
- Incompatible file formats
- Fixed queries/proliferation of application programs
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.
- An entity is a distinct object (a person, place, thing, concept, or event) in the organization that is to be represented in the database.
- An attribute is a property that describes some aspect of the object that we wish to record.
- A relation-ship is an association between entities.
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.
Views View mechanism.
- Provide a level of security.
- Provide a mechanism to customize the appearance of the database.
- Present a consistent, unchanging picture of the structure of the database.
- The structure of the database is called the schema.
- The constraints are sometimes called business rules.