Article - PARTS

From Alistair Cockburn work.

The following concepts may help when speaking about the configuration of a platform. The scale concept is particularly relevant.

precision

How much you care to say about a particular topic. Pi to one decimal place of precision is 3.1, to four decimal places is 3.1416. Source code is more precise than its class diagram, and the assembler code is more precise than the high-level source code. Methodologies manage the evolution of precision over time. Some call for more precision earlier than others, according to the author's fears and wishes.

accuracy

How correct you are when you speak about a topic. To say "Pi to one decimal place is 3.3" would be inaccurate. The final object model needs to be more accurate than the initial one, and the final GUI description is more accurate than the first, low-fidelity prototype. Methodologies manage evolution of accuracy as well as precision.

relevance

Whether to speak about the topic or not. GUI classes are not relevant to the domain model. Infrastructure design is not relevant to collecting user functional requirements. Methodologies typically strive to separate work topics by relevance.

tolerance

How much variation is permitted. Tolerance applies to standards. In coding, a revision code may be required, or it may be left to vary by tool. In writing requirements, designs or programs, the naming, the line breaks, the indentation, may be specified or left to the peoples' discretion, or acceptable bounds may be stated. An example of tolerance in a standard for incremental development would be that a working release must be available every 3 months, plus or minus one month.

scale

How many items are rolled together to be presented as a single item. A "class category" is a scaled view of a set of classes. Scale interacts with precision, in that the dot density of a screen or printer limits the amount of detail that can be put onto one screen or page. However, even if it could all be put onto one page, some people would not want to see all that detail. They want to see a rolled-up or high-level version. Project plans, requirements, designs, all admit of a scaled view. As with geographic systems, maps and mechanical construction, it is possible to put a scale on the deliverable, although it is less consistent. A class category represents a scaling of 1:4 all the way up to 1:30, depending on the number of classes in the class category