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Think about Loose Coupling

Re: Data driven HTTP interaction

by sfink (Deacon)
on Jul 23, 2007 at 05:15 UTC ( #628177=note: print w/replies, xml ) Need Help??

in reply to Data driven HTTP interaction

A couple of quick thoughts:
  • The problem you are addressing is in spirit very, very similar to what addresses. The only difference is that you are communicating over an HTTP connection, whereas Expect communicates over a pseudoterminal. But both are based on a request/reply model.
  • You describe this as "recursion", but to me it seems like that's an artifact of your implementation. You could just as well change either the description or implementation to a series of dependent request/reply transactions. (In general, it seems like the pattern is more of a graph than a tree. Any request could result in a "login timed out" reply, and the subsequent login request would be the same for a whole bunch of different original requests.) You could model it as a state machine, but I think a push-down automaton might be a better fit. Which itself makes me think of YACC -- perhaps its grammar input is a good model for a descriptive format?
  • This also reminds me of Prolog. "My whole task is complete if I add a record for X, make sure the user permissions for Y are set up correctly, and I post an update to the news feed. Adding a record for X is complete if I look up "smurf livers" as a category, and I use that category to define..." etc. Using a similar reduction model, you might be able to figure out what things can be performed in parallel, or at least give nice error output: "Task A failed because subtask c2 failed."

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Re^2: Data driven HTTP interaction
by revdiablo (Prior) on Jul 24, 2007 at 01:37 UTC

    Many thanks for the reply. I'm glad to see you've looked beyond the specific implementation. Your ideas are certainly worth thought.

    I will almost certainly play with the idea in your 2nd point. I may be painting myself into a corner with my current recursive implementation. Your idea seems a lot more flexible, and will probably lead to definitions that are simpler to understand (at least for some definition of "understand").

    I must admit the Prolog-esque solution sounds like a lot of fun. I'm not sure it would be worth the conceptual hurdle, but then again, maybe it would! Hmm.

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