ER Model

Entity-relationship model/entity relationship model

At one of data modeling technique, the model object (the actual world) defining structuring, "the substance" as those which consist of the "relation" you describe the static conceptual data model. It is used for the database design generally.

With the ER model, generally the world (the management object) it expresses with the next three components.

Substance(entity: Entity)
As an object of management those which it defines that "it exists", (example: Physical existence "of customer" "commodity" and so on and legal, logical existence "of company" "branch office" and so on and phenomenon and the like "of contract" "delivered item" and so on).

Attribute(attribute: Attribute)
Those which it defines as quality of the substance. The data elements which the substance has. (Example: "Employee name" "employee address" of employee entity "employee telephone number" and so on.

Relation(relationship: Relationship)
Those which show the relationship of the substance between the substance. The operation for the substance. (Example: ) E.g., employee entity "is assigned" in section entity.

Simultaneously with the model the ER diagram (ERD)was proposed as a notation, but this the database design and data central approach (DOA) because it is practical at the time of system developing in, presently, mainly to be wide it has spread as a standard technique of the data based design.

As for the ER model the Massachusets Institute of Technology (MIT) the Peter chain (Peter P. Chen) departure is something which is displayed 1st VLDB which is held in 1975 (Very Large Data Base) in the conference. As for chain dissertation "The 1976 entity-relationship model: With towards a unifiedview of data "," any all things which exist in society with concrete ones with that abstract ones that, are expression possible with two concepts of the substance and relation ", that you have expressed.

Data central approach (DOA), in the CASE tool, has produced effect on 3 layer schemer structure which ANSI/X3/SPARC proposes as a method of thinking the database structure as a development expedient this thought as a system development methodology. In addition, flowing together with the object oriented which appears as a programming technique to the sixties, it is developmental to the object direction modeling. Furthermore, as a basic model of the semantics database it is used.

However the modeling (analysis) as a technique designates what as the substance and designates what as attribute in the point the ER model the analyst (the designer) it depends on experience and sense (as for the engineering modeling there is also the opinion which we assume that it is possible, even with ER approach with clear decision criterion). Because of that, rather than being used in business analysis, notation of database structure (ERD) has spread mainly.SW