Data Modelling

Data modeling is a method used to define and analyze data requirements needed to support the business processes of an organization. The data requirements are recorded as a conceptual data model with associated data definitions. Actual implementation of the conceptual model is called a logical data model. To implement one conceptual data model may require multiple logical data models. Data modeling defines the relationships between data elements and structures. Data modeling techniques are used to model data in a standard, consistent, predictable manner in order to manage it as a resource. The use of this standard is strongly recommended for all projects requiring a standard means of defining and analyzing the data resources within an organization. Such projects include:

incorporating a data modeling technique into a methodology; 
using a data modeling technique to manage data as a resource; 
using a data modeling technique for the integration of information systems; 
using a data modeling technique for designing computer databases. 

Data modeling may be performed during various types of projects and in multiple phases of projects. Data models are progressive; there is no such thing as the final data model for a business or application. Instead a data model should be considered a living document that will change in response to a changing business. The data models should ideally be stored in a repository so that they can be retrieved, expanded, and edited over time. Whitten (2004) determined two types of data modeling:

Strategic data modeling: This is part of the creation of an information systems strategy, which defines an overall vision and architecture for information systems is defined. Information engineering is a methodology that embraces this approach. 
Data modeling during systems analysis: In systems analysis logical data models are created as part of the development of new databases. 

Data modeling is also a technique for defining business requirements for a database. It is sometimes called database modeling because a data model is eventually implemented in a database.