Conceptual Relationship: Many-to-Many

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See also:

• Conceptual, Logical, and Physical models

Issues:

Duncan Dwelle

• Should many-to-many relationships be allowed to survive in a logical model ? Or should they be modeled into associative entites? The latter allows adding attributes, relationships, and constraints which the automatic many-to-many does not. An associative entity also gives full control over its identiy scheme (e.g., surrogate keys) rather than relying on the automatic inherited concatenated foreign keys as primary.

Charlie Johnson

• Allow attributes to be added to a M:M relationship on the CDM. When the PDM explodes the relationship the attributes are populated from the CDM.

Sharon Getha

• Many methodologies require that many-to-many relationships be resolved prior to generating a physical model.

(In the James Martin & Co. IExpert, Detailed Business Area Analysis, many to many relationships should be resolved with an associative entity, especially if information about that relationship should be captured, like effective dates.It depends on the methodology being used by the company and some tools allow flexibility instead of adhering to one methodology over another.)

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