Is it possible to define a new specialization of InteractionFragment?

Question

The UML specification 2.5.1 defines an abstract class InteractionFragment (17.12.13). The corresponding section of the specification (17.12.13.4) mentions that the following specializations exist: CombinedFragment, Continuation, ExecutionSpecification, Interaction, InteractionOperand, InteractionUse, OccurrenceSpecification, StateInvariant.

Can I define a new specialization? If yes, how, if not, why?

Answer 1

No, you cannot define a new specialization of InteractionFragment according to the UML 2.5.1 specification.

Why Not?

1. Strictly Defined Specializations
   The UML specification (17.12.13.4) explicitly defines the set of existing specializations:

   • CombinedFragment

   • Continuation

   • ExecutionSpecification

   • Interaction

   • InteractionOperand

   • InteractionUse

   • OccurrenceSpecification

   • StateInvariant
     These subclasses fully cover the intended types of interaction fragments within UML.

2. Metamodel Constraints
   UML is a standardized modeling language governed by the Object Management Group (OMG). The metamodel strictly defines how elements can be extended. Interaction fragments are part of UML's behavioral modeling, and extending them arbitrarily would require modifying the UML metamodel itself, which is not supported in standard UML.

3. Lack of Extension Mechanisms for Metaclasses
   UML allows extensions using stereotypes and profiles, but these mechanisms do not allow creating new metaclasses or fundamental specializations of abstract metaclasses like InteractionFragment. Instead, they only allow adding metadata to existing elements.

4. Tool Compatibility
   UML modeling tools are built to support the official metamodel. If you create an unofficial specialization of InteractionFragment, tools that conform to the UML specification would not recognize or support it, making it impractical for interoperability.

What Can You Do Instead?

• Use UML Profiles and Stereotypes
  If you need a custom behavior associated with InteractionFragment, you can define a stereotype in a UML profile, applying it to an existing subclass of InteractionFragment. This approach allows you to add additional properties while maintaining compliance with UML.

• Work with Existing Specializations
  Consider whether your needs can be met by adapting one of the existing specializations, such as CombinedFragment or InteractionUse, rather than introducing an entirely new type.

You cannot introduce a new specialization of InteractionFragment because UML strictly defines its specializations, and the UML metamodel does not provide mechanisms to extend core behavioral elements in this way. Instead, you should use UML stereotypes or work with the existing InteractionFragment subclasses.