Explanatory Models

[ Team LiB ]

Explanatory Models The thrust of this book is that one model should underlie implementation, design, and team communication. Having separate models for these separate purposes poses a hazard. Models can also be valuable as education aids to teach about the domain. The model that drives the design is one view of the domain, but it may aid learning to have other views, used only as educational tools, to communicate general knowledge of the domain. For this purpose, people can use pictures or words that convey other kinds of models unrelated to software design. One particular reason that other models are needed is scope. The technical model that drives the software development process must be strictly pared down to the necessary minimum to fulfill its functions. An explanatory model can include aspects of the domain that provide context that clarifies the more narrowly scoped model. Explanatory models offer the freedom to create much more communicative styles tailored to a particular topic. Visual metaphors used by the domain experts in a field often present clearer explanations, educating developers and harmonizing experts. Explanatory models also present the domain in a way that is simply different, and multiple, diverse explanations help people learn. There is no need for explanatory models to be object models, and it is generally best if they are not. It is actually helpful to avoid UML in these models, to avoid any false impression of correspondence with the software design. Even though the explanatory model and the model that drives design do often correspond, the similarities will seldom be exact. To avoid confusion, everyone must be conscious of the distinction. Example Shipping Operations and Routes Consider an application that tracks cargos for a shipping company. The model includes a detailed view of how port operations and vessel voyages are assembled into an operational plan for a cargo (a "route"). But to the uninitiated, a class diagram may not be very illuminating. Figure 2.4. A class diagram for a shipping route In such a case, an explanatory model can help team members understand what the class diagram actually means. Here is another way of looking at the same concepts: Each line in Figure 2.5 represents either a port operation (loading or unloading the cargo), or cargo sitting in storage on the ground, or cargo sitting on a ship en route. This does not correspond in detail with the class diagram, but it reinforces key points from the domain. Figure 2.5. An explanatory model for a shipping route This sort of diagram, along with natural language explanations of the model it represents, can help developers and domain experts alike understand the more rigorous software model diagrams. Together they are easier to understand than either view alone.

[ Team LiB ]