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modelling [message #259753] Thu, 16 August 2007 07:00 Go to next message
kirank05
Messages: 6
Registered: August 2007
Location: Hyderabad
Junior Member
Hi all,

Hereby i am attaching sample data model with one-to-many relationships.I want to set it as application with system as many-many relationship.could you please suggest me how do i set it as many-to-many relationships.


thanks in advance



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Re: modelling [message #281883 is a reply to message #259753] Mon, 19 November 2007 17:26 Go to previous message
patrickhaston
Messages: 11
Registered: November 2007
Junior Member
Hi,

You may have a solution already.

In general, the way you model a many to many relationship is through the creation of an intersection table. This is an artificial table that may contain no data other than the fact that the two items in question are related, or you may choose to add attributes that define the nature of their relationship or something else entirely.

In your example you have tables MD_SYSTEM and MS_APPLICATION. To create a many-to-many relationship you could create a table called MD_APPLICATION_SYSTEM. This is often modelled as having a composite primary key made up of the primary keys of the two related tables, which double up as foreign keys. In your example this would be SYSTEM_ID and APPLICATION_ID.

Does this answer your question?

Patrick.
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