What is data model?

Data is sign record of describing objects. Model is an abstract of the real world. A data model in software engineering is an abstract model that describes how data is represented and accessed.

Data models formally define data elements and relationships among data elements for a domain of interest. Data model explicitly determines the meaning of data, which in this case is known as structured data. Typical applications of data models include database models, design of information systems, and enabling exchange of data. Usually data models are specified in a data modeling language. A data model can be sometimes referred to as a data structure, especially in the context of programming languages.

Described data model includes three parts: data structure, data manipulation, and data constraint.

Data structure describes the data type, content, an association between data and so on. Data structure is the basis of data model, and data manipulation and constraints are built on the data structure. Different data structures have different data manipulation and constraints.

Data manipulation describes the operation type and ways on the data structure.

Data constraint describes the data syntax, association of semantic between the data in data structure, and the interdependence & constraint between data, the rule of data with dynamic change, which in order to make the data correct, effective and compatible.

Data model may be divided into three kinds in the different application levels:

Conceptual Data Model: It describes the semantics of a domain, being the scope of the model. For example, it may be a model of the interest area of an organization or industry. This consists of entity classes, representing kinds of things of significance in the domain, and relationships assertions about associations between pairs of entity classes. A conceptual schema specifies the kinds of facts or propositions that can be expressed by using the model. In that sense, it defines the allowed expressions in an artificial 'language' with a scope that is limited by the scope of the model.

Logical Data Model: It describes the semantics, as represented by a particular data manipulation technology. This consists of descriptions of tables and columns, object oriented classes, and XML tags, among other things.

Physical Data Model: It describes the physical means by which data are stored. This is concerned with partitions, CPUs, table spaces, and so on.

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