The entity-relationship model (or ER model) is a way of graphically representing the logical relationships of entities (or objects) in order to create a database. The ER model was first proposed by Peter Pin-Shan Chen of Massachusetts Institute of Technology (MIT) in the 1970s.
In ER modeling, the structure for a database is portrayed as a diagram, called an entity-relationship diagram
(or ER diagram), that resembles the graphical breakdown of a sentence into its grammatical parts. Entities are rendered as points, polygons, circles, or ovals. Relationships are portrayed as lines connecting the points, polygons, circles, or ovals. Any ER diagram has an equivalent relational table, and any relational table has an equivalent ER diagram. ER diagramming is an invaluable aid to engineers in the design, optimization, and debugging of database programs.
In a logical sense, entities are the equivalent of grammatical nouns, such as employees, departments, products, or networks. An entity can be defined by means of its properties, called attributes. Relationships are the equivalent of verbs or associations, such as the act of purchasing, the act of repairing, being a member of a group, or being a supervisor of a department. A relationship can be defined according to the number of entities associated with it, known as the degree.
RELATED GLOSSARY TERMS: relational database, database management system (DBMS), OLE DB (OLEDB or Object Linking and Embedding Database), flat file, Fast Guide: SQL Server 2000 commands, comma-separated values file (CSV), information, full-text database, DDBMS (distributed database management system), relational database management system (RDBMS)
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