TUTORIAL-ADVANCED-TYPES.md

TRLC Tutorial (Advanced types tips and tricks)

This is part of the TRLC Tutorial.

Type Qualifiers

There are two modifiers available when declaring types: abstract and final. These may be useful for larger organisations where you have a more central requirement team and many users of these centrally defined types.

Abstract Types

A type marked abstract must be extended before it can be used. For example:

abstract type Base_Requirement {
   description optional String
}

type Requirement extends Base_Requirement {
   derived_from Base_Requirement [1 .. *]
}

type Top_Level_Requirement extends Base_Requirement {
}

In this example you can create objects of type Requirement or Top_Level_Requirement, but you cannot create instances of Base_Requirement.

Final Types

A type marked final cannot be extended with new components. However users are still allowed to extend it with new checks or freeze any components they like.

Building on the above example:

final type Supplier_Requirement extends Requirement {
   supplier_name String
}

type ACME_Requirement extends Supplier_Requirement {
   freeze supplier_name = "ACME Corporation, Inc."
}

This makes sure that any and all supplier requirements are completely uniform, and nobody adds new fields that may be confusing or unexpected to the suppliers.