3.2.1 Textual analysis
Because a class is conceptually a set of objects of the same kind, and objects represent ‘things’ in the system domain, nouns and noun phrases in the requirements document can be used as an aid to identifying possible classes. A noun phrase is a phrase (a sequence of words like ‘number of copies’) that functions as a noun – and which can be used anywhere that a noun could be used.
Below is an extract from the requirements document for a DVD Library System with the nouns and noun phrases underlined. We have not included the acceptance tests, as these are derived from the use cases, so do not add anything to the description of the system.