Derivation of Classes from Use Cases Automatically Generated by a Three-Level Sentence Processing Algorithm

Identification of classes from a requirements specification is one of the most important and difficult tasks during analysis and design of new object- oriented systems. Recent developments in CASE tool research have begun incorporating quite sophisticated natural language processing techniques to help generate class diagrams; however, considerable problems remain in the form of overlooked and/or excess classes. The difficulty stems largely from inherent ambiguity in written language; and a general lack of conciseness and completeness in requirements specifications. We argue that a more effective approach is to obtain classes from use cases, rather than directly from the specification. Our justification is that use cases describe specific functionalities of the system, and therefore the candidate objects involved in effecting those functionalities. To that end, we propose an algorithm to i) extract use case sentences from requirements, ii) validate functional specifications in each sentence of the use cases so that classes can be identified, and iii) reuse previously validated, domain- dependent use cases to supply missing functional specifications that may contain participating classes. Thereafter, classes are automatically obtained from these generated use cases. Problems arising from ambiguity in the written requirements are mitigated by imposing a small number of restrictions on the language that can be used for writing requirements, and the sentence structure of use cases is formalized.