You can organize your use case model by functionally related areas (subsystems), by release, or both. One useful strategy is to identify all the use cases within a functional area on the use case diagram, but write the narrative descriptions only for the use cases that will participate in the current release.

Model Based Systems Engineering provides the flexibility and expressiveness to define complex systems quickly effectively by reusing common entities across design projects. A Library is a package containing many reusable subsystems, parametric constraints, common data types and common value types, dimensions and units. The following diagram shows an example library model.

In the example Library, each of the child packages contains child models that capture the following reusable entities:

1. Blocks defining systems such as those listed in the Components package, or those defined in the External package.
2. ConstraintBlocks defining parametric constraints for use in parametric models.
3. Value Types describing quantities, expressed as measurable dimensions in specific units.
4. Data Types and Flow Specifications describing data structures and Flows.