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by Martin Fowler.
Original Post: RequestStreamMap
Feed Title: Martin Fowler's Bliki
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Feed Description: A cross between a blog and wiki of my partly-formed ideas on software development
Hang around my colleagues at ThoughtWorks and you soon get the
impression that the only good Enterprise Service Bus (ESB) is a dead
ESB. Jim Webber refers to them as Egregious Spaghetti Boxes. So it's
not uncommon to hear tales of attempts to get them out of systems
that don't need them.
Battle was joined at one client and it brought to mind my younger
days playing D&D. Webber swings but misses as the ESB is AC 2,
Evan gets a hit and rolls 2d8 for 6 damage. Erik finally kills it
by casting "Summon Request Stream Map".
So what was Erik's
decisive spell? Essentially the idea was to take a simple request
and show how the data for the request and response made their way
through the layers of the application. Erik printed out all the code
that you needed to read to understand how this would work - which
ran to several pages. He also produced this diagram.
It's currently fashionable in agile circles to do Value Stream
Mapping as a way to uncover waste in a software development
process. I think of this as a request stream map because it similarly
takes a request and shows how it moves through the layers allowing
us to visualize what's going on and think about the cost and value of
the layers.
Layering is an essential tool for building software
applications. But like most essential things in life, excess can
be almost as much of a problem as too little. A visualization like
this (or the multiple pages of code) can help you find where "just
enough" is.
One hazard, however. If you do need to transform data from one
form to another, it's usually better to a few little
transformations than one big transformation. You want to avoid
unnecessary transformations not compress the ones you need.
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