linkage

linkage is one or many optional nested definitions within UDTs defining relationships to other types.

Linkage is used to express named, loosely-coupled relationships between types.

• entity, key, record and trait support nested linkage definitions.

• A linkage has an associated name. Multiple uniquely named linkages can be associated with a user-defined type. Linkages defined in traits become part of UDTs that includes the trait.

• A linkage can be denoted as 1-to-1:

  // Outer type definition
  ...
     linkage <Unique linkage identifier 1>
              ( < list of columns from current type > )
            < linked type name >
              ( < list of columns from linked type > )
  

• As optionally 1-to-1:

  // Outer type definition
  ...
     linkage <Unique linkage identifier 1>
              ( < list of columns from current type > )
            < linked type name > ?
              ( < list of columns from linked type > )
  

• Or as 1-to-many using a list of targets:

     linkage <Unique linkage identifier 2>
              ( < list of columns from current type > )
             list< < linked type name > >
              ( < list of columns from linked type > )
  ...
  

Visualising Linkages

Linkages are displayed alongside the model documentation, as shown in the example below.