An ER model can also be expressed in a verbal form, for example: one building may be divided into zero or more apartments, but one apartment can only be located in one building.Įntities may be characterized not only by relationships, but also by additional properties ( attributes), which include identifiers called "primary keys". It is usually drawn in a graphical form as boxes ( entities) that are connected by lines ( relationships) which express the associations and dependencies between entities. It does not define the business processes it only presents a business data schema in graphical form. 3 Entity–relationships and semantic modelingĪn E-R model is usually the result of systematic analysis to define and describe what is important to processes in an area of a business. ![]() ![]()
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