Evolution of software systems is prompted by all sorts of changes. This paper demonstrates how the use case, a well known construct in object-oriented analysis, is adapted to form the change case, to identify and articulate anticipated system changes. A change case provides the ability to identify and incorporate expected future change into a design to enhance the long-term robustness of that design. In this paper, we define change cases and demonstrate how change cases are captured by the analyst. We present examples to illustrate how change cases can influence present system design and point the way toward designs that more easily accommodate expected future changes. Change cases can be effectively employed in the context of any methodology that supports use cases and traceability links.

INKA is a natural language interface to facilitate knowledge acquisition during expert system development for electronic instrument trouble-shooting. The expert system design methodology develops a domain definition, called GLIB, in the form of a semantic grammar. This grammar format enables GLIB to be used with the INGLISH interface, which constrains users to create statements within a subset of English. Incremental parsing in INGLISH allows immediate remedial information to be generated if a user deviates from the sublanguage. Sentences are translated into production rules using the methodology of lexical-functional grammar. The system is written in Smalltalk and, in INKA, produces rules for a Prolog inference engine.

This paper presents a model for deterministic parsing which was designed to simplify the task of writing and understanding a deterministic grammar. While retaining structures and operations similar to those of Marcus' PARSIFAL parser [Marcus 80] the grammar language incorporates the following changes. (1) The use of productions operating in parallel has essentially been eliminated and instead the productions are organized into sequences. Not only does this improve the understandability of the grammar, it is felt that this organization corresponds more closely to the task of performing the sequence of buffer transformations and attachments required to parse the most common constituent types. (2) A general method for interfacing between the parser and a semantic representation system is introduced. This interface is independent of the particular semantic representation used and hides all details of the semantic processing from the grammar writer. (3) The interface also provides a general method for dealing with syntactic ambiguities which arise from the attachment of optional modifiers such as prepositional phrases. This frees the grammar writer from determining each point at which such ambiguities can occur.