What are relations on Extended Data Types used for?

I can see that Extended Data Types can have Array Element which seems to make it a composite type. I'll be looking into that later.

What are the relations used for? MSDN was woefully crap at explainined what it would actually be used for. Why would you want to relate a type to a specific ta开发者_JAVA百科ble and why would other tables using the type care?

When I create a new 'PersonTable' table I could have a key field called personId, creating/using a new Extended Data Types called personId and adding the relation you've mentioned. Now when I add our EDT to other tables we do not have to specify either labels or relations to our PersonTable as this it's defined by the extended data type.

In a related form (e.g. PersonSkillsTable) where our personid field has been added to an existing table it will now automatically create the dropdown/grid to select a value from our persontable. We didn't need to add our persontable to the form's Data Source.

1. Automatic relations between tables
2. Automatic lookups
3. Automatic "Go To Main Table" menu option after right-click