To follow up on my cardinality post, a very useful function is AutoNumber. AutoNumber will create an integer for each distinct value in your defined namespace, which is usually a field. The second parameter, allows you to define the namespace, which means you can use it across multiple fields while keeping data association integrity.
The best use case for AutoNumber is for keys. This will create the smallest footprint for your key fields and maintain the relationship.
One tip, apply AutoNumber at the end of you data model build. It is much easier to troubleshoot data model issues when you can see the actual data. After you know those linkages are good, then utilize the function.