Presentation
A data model is used to represent the static structure of a system, particularly the types of objects manipulated in the system, their internal structure, and the relationships between them.
An object is an entity with a well-defined boundary and identity that encapsulates state and behavior. Its state is represented by the values of its attributes and its relationships with other objects. An object is an instance of a class.
Examples of objects:
• Business objects:
• John Williams, Elizabeth Davis and Paul Smith are instances of the “person” class.
• Orders 10533 and 7322 are instances of the "order" class.
• SPD-1730 Monitor is an instance of the “item” class.
Data modeling consists of identifying the entities representing the activity of the company, and defining the associations existing between them. The entities and associations in the data diagram associated with a sector of the company must be sufficient to provide a complete semantic description. In other words, one should be able to describe the activity of a company by using only these entities and associations.
This does not mean that each word or verb used in this explanation corresponds directly to an object in the data diagram. It means that one must be able to state what is to be expressed using these entities and associations.
Data diagram specification is often considered the most important element in modeling of an information system.