Re: The End Of Technical Writing

Subject: Re: The End Of Technical Writing
From: Tony Markos <ajmarkos -at- yahoo -dot- com>
To: "TECHWR-L" <techwr-l -at- lists -dot- techwr-l -dot- com>
Date: Wed, 27 Oct 2004 18:20:34 -0700 (PDT)

--- Dick Margulis <margulisd -at- comcast -dot- net> asks:

.....When I've worked with DFDs they have been very
instructive in terms of software design (what messages
flow in which direction between software
modules; what data goes in and out of which db
tables); but they have had little or nothing to do
with user tasks....

Tony Markos responds:

Key concept: Data Flow Diagrams have nothing
inherently to do with computer systems analysis or
design. DFDs where first used almost fifty years
before the computer was invented. In the late 1890's
there were no software functions, just people and
their tasks.

DFDs can be used for tech comm of computer systems,
but they can just as easily be used to document
completely manual procedure.

Dick Margulis asks:

How do they [DFDs] differ from use case diagrams?

Tony Markos responds:

Hugely - especially for task analysis! I recently
initiated a thread on the Requirements Engineering
listserv that included discussion of this very matter.

Data Flow Diagrams actually prompt you through a task
analysis. With DFDs we follow each data flow from
start to finish. When the flows in our DFD naturally
combine or split apart, we have "flushed-out" an
essential task that may otherwise have gone
undiscovered. Thats what analysis is - a discovery

In contrast, with Use Case diagrams, we are forced to
play the old connect-the-box (or oval) game: We draw
Use Case ovals for the tasks that happen to pop into
our mind; then, we try to connect each oval to actors
and/or other Use Case ovals. This results in the age
old problem: Whenever we try to perform analysis buy
connecting together boxes, as opposed to following the
data flows, we are going to miss a lot of important
tasks - especially in larger-scale analysis efforts.

Avoidance of Connect-The-Box is THE fundamental
principle behind DFDs.

The other very important difference between Use Cases
and Data Flow Diagrams for task analysis is that Use
Cases are fundamentaly a bottom-up analysis technique
(at least compared to DFDs). DFDs are a true top-down
technique. Whenever we try performing a larger-scale
analysis in a bottom-up fashion, we end up "drowning
in an ocean of detail".

Tony Markos

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Re: The End Of Technical Writing: From: Dick Margulis

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