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Conclusion

Option D: Formal ACM

Purpose: To ensure that any information relating to static elements is specified within Rose, using the analysis class stereotypes, described centrally in Rose. Soda can present these ACMs as part of the Use Case document.

In semantics this approach is no different to the previous option. What differs though, is the ACM becomes a deliverable in its own right, and is centrally maintained in Rose. As new terms are identified in a use case flow, they must be first evaluated against what is already present in the model.

In addition, attributes are added to entities, to describe in logical terms the information needs of these.

Example of enriched formal ACM

The ACM offers the designers at the end of elaboration an enterprise view of architecturally significant terms, derived directly from the use cases. This should provide sufficient context in which the designers can define their separate design model.

Another purpose of a formal analysis model is to close the gap between any underlying reference data and the business understanding of it, and then to tie this with the use case deliverable - i.e. creating an abstract description of this data for mapping and validation purposes.

The importance of this point could tip the balance between the informal approach above (which does not support this) and the approach described here.

Advantages

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Enterprise view of architecturally significant terms that cuts across Use Cases

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Moving away from reliance of just “word” artefacts to define scope of analysis promotes a higher quality, more robust deliverable to design team.

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An ACM without design terms should prove a cycle independent deliverable as it is not tied to the implementation or solution.

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Will act as reviewable bridge to implementation persistence model.

Disadvantages

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Formal ACMs inevitably evolve into design as the cycle matures (without appropriate checks and balances), and as they a slightly further removed from the Use Cases, such trends become harder to resist.

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Producing the “perfect” ACM becomes an disproportionate activity of the analysis team (becomes introspective)

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Even where separately defined design model is enforced, in practice it is hard to validate the trace from design and analysis views, with the consequence that the ACM becomes sidelined.

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Version control

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To mitigate the above requires greater maintenance and control – possible a full time role.

Option E: Sequence model

Purpose: To ensure that terms described in the ACM have their responsibilities defined by using at least one sequence model per Use Case.

This extends the formal ACM. For each use case, ACM terms impacted by it are shown in one or more sequence models (depending on complexity this could be one per flow – although for simpler use cases these could be combined).

: Example of sequence model

Advantages

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Description of responsibility as well as association and attributes makes the ACM “complete”

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Very useful for testing purposes

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Restores coupling between Use Case and terms described in a formalised ACM.

Disadvantages

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The structure of this artefact means that slipping into design mode is very difficult to resist (for example in the above example contextual information must be shown to come from somewhere to make the model complete. However the decision to make the log-on screen the boundary for this is a design decision)

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Can be expensive to produce as at the very least it will require one model per Use Case

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© 2002-2005 Codel Services Ltd

This paper has been prepared by Codel Services Ltd to illustrate how structured business modelling can help your organisation. Codel Services Ltd is an IT Consultancy specialising in business modelling. If you would like further information, please contact us at: Deryck Brailsford, Codel Services Ltd, Dale Hill Cottage, Kirby-Le-Soken, Essex CO13 0EN,United Kingdom. Telephone: +44 (0)1255 862354/Mobile: + 44 (0)7710 435227/e-mail: info@codel-services.com