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I am building a Entity-Relationship diagram in Vision 2010 using crow's feet. Everytime I connect to tables with a relationship the following element appears near the "many" side.

u:R d:R

I can click on the element and delete it but would like to know what it is used for, obviously it has to do with Relationship.

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A screenshot might help loads here –  Journeyman Geek Feb 2 '13 at 7:47
    
@JourneymanGeek: See below. –  Karan Feb 4 '13 at 2:07
    
ahh right. I wasn't asked to do that on my database course, and I sort of ended up using another tool, which probably explains my unfamiliarity with it ;p –  Journeyman Geek Feb 4 '13 at 2:18

1 Answer 1

Example:

1

The notation represents Update and Delete operations enforced by referential integrity rules.

If a Primary Key (PK) is linked to a Foreign Key (FK) in another table, we need to ensure that referential integrity is maintained. Depending on what makes business sense, the update rule can be either:

  • U:R (Update:Restrict) – Disallow updates of values in the PK
  • U:C (Update:Cascade) – Allow updates, but cascade changes to all related FKs in other tables

Similarly, the delete rule can be either:

  • D:R (Delete:Restrict) – Disallow deletion of records
  • D:C (Delete:Cascade) – Allow deletion of records, but cascade deletions in all related tables that contain a FK linked to this table

Notations available in Visio are:

  • R (No action) - Don't change the child table
  • C (Cascade) - Replicate the change in the child table
  • D (Set default) - Insert the default value you previously set for that column in the child table
  • N (Set Null) - Set the child table to NULL
  • (Blank) - Do not enforce referential integrity on the relationship

See the Preserve referential integrity in Database Model diagrams article for more details.

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