January 24
The Conceptual Model: Designing Analysis Classes

• A conceptual model is a description of the "real world" problem domain, not of a software design.
• Concept: idea, thing, or object
• A concept has:
• Intension: its definition.
• Representation: its name, symbol, or picture.
• Extension: its set of instances.
• Complexity of a problem handled by decomposition (AKA divide-and-conquer).
• Structured analysis: functional decomposition.
• Object-oriented analysis: conceptual decomposition.
• Analogy: conceptual modeling as mapmaking.
• Use existing names: describe the problem as the user understands it.
• Exclude unimportant features: if it comes up in a use case, include it.
• Don't include what isn't there: KISS, and avoid mission creep.
• Useful rules of thumb in identifying concepts:
• Use concept categories and noun phrases to highlight potential concepts.
• If potential concept X is simply a numeric value or a text string, it is more likely an attribute of a concept rather than a concept itself.
• If X has internal structure, it probably is a concept.
• Example: Age and Family Name are probably attributes, but Person, which includes first name, last name, age, and other attributes, has an internal structure and so is a concept.
• Note, though, that "concept" is defined recursively. A concept's intension may include other concepts.
• If in doubt during analysis, include it. It's easier and cheaper to cut a concept during design than to add one.
• CRC cards are a good way to begin organizing your conceptual model.
  1. Use cases tell you what the user wants.
  2. CRC cards help you get a handle on the conceptual model.
  3. Class diagrams formalize your understanding of the conceptual model.

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