DATA MODELS

Data models include a set of basic operations for specifying retrievals and updates on the database. Data models also allow the database designer to specify a set of valid user defined operations on the database objects. Depending on the nearness of the data models with the users, data models can be classified in the following categories:

• High-level or conceptual data models: This class of models provides concepts that are based on entities and relationship. It uses concepts such as entities, attributes and relationships.

1. Entity: An entity represents a real-world object or concept, such as employee or a project that is described in the database.
2. Attribute: An attribute represents some property that describes an entity, such as the employee's name or salary.
3. Relationship: A relationship among two or more entities represents an interaction among the entities (e.g., relationship between an employee and a project).

• Low-level or physical data models: this model describes the details of how data is stored in the computer (useful for computer specialists).

• Representational or implementation data models: These models provide concepts that are between the above two extremes which may be understood by end users-record-based, object-oriented etc.