Building the Analysis Model › Performing Decomposition › Parallel Decomposition Heuristics

Parallel Decomposition Heuristics

While not all are inviolable rules, any decomposition that fails to conform to these heuristics should be considered suspect:

• Each level of decomposition should yield between three and seven subordinate elements.
• If more than seven subordinate elements are discovered, introduction of an intervening super-ordinate level should be considered.
• Each primitive subject area should generally yield no more than 10 entity types.
• If more than 10 entity types are found, there is probably another central entity type in the primitive subject area.
• The expected number of entity types per primitive subject area in a typical model is eight.
• It is unusual (although not impossible) for a primitive subject area to yield fewer than six entity types.
• In such a case, it is likely that the entity types have been misclassified.
• The average number of elementary processes into which a primitive function eventually decomposes in a typical model is 27.
• That is, each primitive function decomposes into three high-level processes, which decompose into three processes apiece, which in turn decompose into three elementary processes each.
• A primitive subject area and its associated primitive function should be correspondingly complex.
• If the primitive subject area is simple (that is, includes fewer than the expected eight entity types), the associated primitive function should also be simple (that is, decompose into fewer than the expected 27 elementary processes).
• If the primitive subject area is complex, the primitive function should also be complex.
• There is no strict rule here, but if a model includes only three entity types that require 60 elementary processes to deal with them, something is askew.
• When decomposing a primitive function into its directly subordinate processes, those processes should be clearly recognized as dealing with the central entity type of the corresponding primitive subject area.
• At the next level of process decomposition, processes may be discovered that deal with both the central entity type and its dependents.
• This guideline helps to confirm that the primitive subject area and its corresponding primitive function truly correspond.