Developing initial OOA models

The authors developed an initial object-oriented requirements model for an existing missile planning system. They adopted two approaches: a bottom-up approach in which object-oriented model fragments were constructed that corresponded to segments of the requirements documents, and a top-down approach that was driven by the construction and analysis of scenarios. The strengths and limitations of each approach were discussed in the context of the example. A bottom-up, fragment-driven approach is appropriate in cases where there is a large, rich body of documentation. A top-down, scenario-driven approach should dominate where there is no requirements specification, but some high-level, unintegrated information about how the system should operate