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Irritated


Unsurprisingly, one of BD00’s posts irritated a reader who stumbled upon it. For some strange reason, BD00’s scribblings have that effect on some people. In the irritating post, “The Old Is New Again“, BD00 referred to Data and Control Flow diagrams as “old and obsolete“. In caustic BD00 fashion, the reader commented:

Use Cases and Activity Diagrams, in contrast (to the Data Flow diagram), offer little guidance in effective partitioning. They rely upon the age old “sledge hammer” approach to partitioning” (ie, just break-er-up any way you can). Sledge hammer partitioning is what cave men used to partition entities. So in a critical sense, DFD’s are new and hip, while Use Cases and Activity Diagrams are based upon logic that is older than dirt.

BD00 likes all visual modeling tools – including the DFD hatched during the heyday of structured analysis. BD00 only meant “old and obsolete” in the sense that DFDs pre-dated the arrival of the UML and the object-oriented approach to system analysis and design. However, BD00 did feel the need to correct the reader’s misunderstanding of the features and capabilities that UML Activity Diagrams offer up to analysts/designers.

Both the DFD and UML activity diagram pair below equivalently capture an analyst’s partitioning design decision (where DFD Process X == Activity Diagram Action X). Via “swimlanes“, the lower activity diagram makes the result of a second design decision visible: the conscious allocation of the Actions to the higher level Objects that will perform them during system operation. So, how are UML activity diagrams inferior to DFDs in supporting partitioning? A rich palette of other symbols (forks, joins, decisions, merges, control flows, signals) are also available to analysts (if needed) for capturing design decisions and exposing them for scrutiny.

DFDs and UML diagrams are just tools – job performance aids. Learning how to use them, and learning how to use them effectively, are two separate challenges. Design “guidance” for system partitioning, leveling, balancing, etc, has to come from somewhere else. From a mentor? From personal experience learning how to design systems over time? From divine intervention?

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