A data model a collection of concepts that can be used to describe the structure of a database provides the necessary means to achieve this abstraction. By structure of a database we mean the datatype,relationship and constraints that apply to the data.Most data models also include a set of basic operations for specifying retrievals and update on the database.
Categories of Data Models
Data model categories according to the concept they are describe the database structure. These models are
- High level or conceptual data model.
- Low level or physical data model.
- Representational data models.
Conceptual data model or high level data model
Conceptual data model provide concepts that are close to the way many users perceives data. That model use concept such as an employee or a project or a project that is described in the database.
An attribute represent some property of interest that further describe an entity. Example name is attribute of entity employee.
A relationship among two or more entities represent association among the entities.Example a workon relationship between employee and project.
Entity Relationship model a high level conceptual data model.
Physical data model or Low level data model
Physical data model describe how data is stored as files in the computer by representing such as record formats,record ordering and access paths.
Access path is a structure that makes the search for particular database record efficient.
An index is an example of an access path that allows direct access to data using an index term or a keyword.
Representational data model or implementational data model
Representational data models are the models used most frequently in traditional DBMS.These include relational data model as well as legacy data model that are hierarchical models.Representational data models represent data by using record structures and hence are sometimes called record based data model.
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