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    Wednesday, 6 March 2024

    Extended E-R Features

    Extended ER is a high-level data model that incorporates the extensions to the original ER model. Enhanced entity-relationship diagrams are advanced database diagrams very similar to regular ER diagrams which represent the requirements and complexities of complex databases. 

    Enhanced ER Model concepts are:

    • Generalization
    • Specialization
    • Aggregation

    Generalization

    Generalization is a bottom-up approach in which two or more entities can be generalized to a higher-level entity if they have some attributes in common.

    It is the process of extracting common properties from a set of entities and creating a generalized entity from it. This process combines a number of entity sets that share the same features into higher-level entity sets.

    Generalization is used to emphasize the similarities among the lower level entity sets and to hide the differences.


    Specialization

    In specialization, an entity is divided into sub-entities based on its characteristics. It is a top-down approach where the higher-level entity is specialized into two or more lower-level entities. 

    The process of designing sub groupings within an entity set is called specialization. Lower level entity sets inherits all the attributes and relationship of the higher level entity set to which it is linked.

    Specialization can be depicted in E-R diagram by a hallow arrow-head pointing from specialized entity to the other entity.

    Aggregation

    Aggregation allows us to indicate that a relationship set participates in another relationship set. It is an abstraction in which relationship sets are treated as higher level entity sets and can participate in relationships.

    Aggregation allows relationships between relationships. Aggregation treat relationship as an abstract entity.




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