Elaborating the Linear Model

We tried to review, then extend the strawperson model in the position paper. This was a linear model arranged in order of increasing separability of system from domain model representations:

a.

Use of single system model as domain model: One system diagram is used to denote the domain model. If the system model includes only a high level of detail it may be called a generic architecture (particularly if it fits on one page!).

In this approach the "system model used as domain model" includes only those portions that are deemed COMMON within the domain, and excludes portions that are deemed VARIABLE. This approach can therefore be said to make the commonality EXPLICIT, but leave the variability IMPLICIT.

(Question: is it the same whether a given representation does not include given data, or includes it in an undifferentiated fashion? Because in a sense the strategy above may leave the variability unrepresented, rather than represented but implicit.)

b.

Use of multiple system models as (implicit) domain model: In this approach multiple system models are used to implicitly suggest a domain model. Here, the assumption is that variability is expressed directly in differences across the individual models. One drawback of the approach may be that commonality is left implicit. That is, it is only the intuition of the observer that pulls out perceptions of common elements and structural features through inspection across several similar diagrams.

c.

Use of hierarchical levels within a system model to indicate boundaries between system and domain representations

d.

Annotated or augmented system model representations to indicate domain variability

e.

Use of system modeling representations with built-in semantics for variability as domain modeling representation (e.g., OO)

f.

Separate representations for domain commonality- variability.

In discussing this linear model, the categories began to break down as we made finer sets of distinctions within categories. (For example, use of hierarchical levels (strategy 3) was further broken down according to whether specializations or instantiations were involved.)