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Telelogic System Architect (steve huntington) | ![]() |
Topic Title: Extended Entity Relation Topic Summary: Is there a way to model Extended Entity Relationship in SA? Created On: 15-Aug-2006 21:06 Status: Read Only |
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Is is possible to make such a model in SA and then convert it to class models (UML) and also to physical table (relational tables)?
Extended (or Enhanced) Entity Relation model is an ER data modeling that includes aggregation, composition, specialization/generalization (and constraints on them), etc... TIA Michele Dessureault |
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Assuming that your definitions are as follows:
Aggregation - where one attribute is said to be derived by aggregating others; e.g. Annual_Total_Amount = Monthly _Total_Amount aggregated over a year.
Composition - where one atribute is made up froma concatenation of others; e.g. Delivery_Point_Ref is a concatenation of Customer_Ref, Postcode and Start_Date
These concepts are not part of the Relational model - they are not logical constructs, they are implementation strategies or historical physical system limitations. These are potential considerations during physical database design, being concerned with Tables and Columns, rather than Entities, Attributes and Relationships.
SA does not natively support the modelling of ETL rules, or 'Mappings' from data source(s) to target(s).
Aggregations and concatenations as defined here are strategies for use in physical database design, particularly when constructing Data Warehouses or similar reporting based structures, and may only be modelled in SA using end-user customisations. Get busy with USERPROPS!
As far as specialisation and generalisation are concerned, these are represented in the Relational model by Entity Subtyping, which allows a logical superype to have multiple logical subtypes, each subtype being a specialisation of the supertype (the generalisation).
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Thank you Mark for your answer!
However, I mean aggregation and composition as in UML classes. When reading your answer, I am not sure this is what you also mean. Can you be more precised on that matter and also according to that meaning? TIA, Michèle Dessureault |
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