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An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between entities (instances of those entity types).
An associative entity is a term used in relational and entity–relationship theory. A relational database requires the implementation of a base relation (or base table) to resolve many-to-many relationships. A base relation representing this kind of entity is called, informally, an associative table. An associative entity (using Chen notation)
A sample ER diagram. Database requirements for a CD collection in EXPRESS-G notation.. In 1976, an entity-relationship (ER) graphic notation was introduced by Peter Chen.He stressed that it was a "semantic" modelling technique and independent of any database modelling techniques such as Hierarchical, CODASYL, Relational etc. [2] Since then, languages for information models have continued to ...
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Chen's main contributions are formalizing the concepts, developing a theory with a set of data definition and manipulation operations, and specifying the translation rules from the ER model to several major types of databases (including the Relational Database). He also popularized the model and introduced it to the academic literature.
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In systems analysis, a one-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model). For example, take a car and an owner of the car. The car can only be owned by one owner at a time or not owned at all, and an owner could own zero, one, or multiple cars.
Fully Communication Oriented Information Modeling (FCO-IM) is a method for building conceptual information models.Such models can then be automatically transformed into entity-relationship models (ERM), Unified Modeling Language (UML), relational or dimensional models with the FCO-IM Bridge toolset, and it is possible to generate complete end-user applications from them with the IMAGine toolset.