I’ve already written about my systems-led approach to accessibility research. This series of articles is designed to put a little more flesh on the bone with a detailed look at how OOA/OOD (Object Oriented Analysis and Design) can be used to describe computer systems and their interaction with users.
2.2 A thinking tool
The choice of systems modelling was guided by a need to describe abstract behaviour, not by a need to design and implement large computer programs (although this is a logical follow-on). It was therefore necessary to consider which notational elements of the selected method would be of most use in describing free-standing abstract models and concepts.
Shlaer and Mellor is a powerful tool in this respect as it focuses on expressing information, rather than program structure, with its main diagram, the Information Model (IM) targeted at expressing association relationships. That is to say, it is more tailored towards, “House is mortgaged to bank” than, “House is composed of four walls, a roof, doors, and windows”. Both can be expressed within the notation, but the former is encouraged by the method. It is this focus on describing application-level problem domains that both distinguish it from its predecessor methods such as Jackson Structured Programming (Jackson, 1975) and Yourdon Structured Analysis and Design (Yourdon, 1989), and make it a useful tool in expressing the organization of information.
Confidence in choosing the method also comes from Shlaer and Mellor’s own intentions for their method:
Moving up a level, we can say that an information model is a thinking tool used to aid the formalization of knowledge. It helps us to work out how we want to think about a problem: the terms we need to define, the assumptions we make in selecting those terms, and the consistency of our definitions and assumptions.
(Shlaer & Mellor, 1988, p. 7).
In addition to a single Information Model, the method also explicitly supports organization of large Information Models, allowing them to be expressed as smaller subsystems using the Subsystem Relationship Model (SRM). Considering the complexity of human physiology, and the potential size and complexity of user interfaces and the content that they express, this provides an added advantage for the Shlaer and Mellor route.