Re: Friendly amendment #2c [Re: Straw poll on "synchronous" definitions]

  ----- Original Message ----- 
  From: Anne Thomas Manes 
  To: Walden Mathews ; Christopher B Ferris ; www-ws-arch@w3.org 
  Sent: Saturday, March 15, 2003 6:11 PM
  Subject: RE: Friendly amendment #2c [Re: Straw poll on "synchronous" definitions]


  The biggest issue I have with Ugo's definition (and all the others) is that they tie synchrony with blocking versus non-blocking.

  [wm] Agree.  A better definition can show the relation to these concepts, too.


   Synchronous means "at the same time". Asynchronous means "not at the same time". Whether or not the sender has to wait idly for a response is a separate issue.


  [wm] You've been cheating by looking at the dictionary!  But check this out:

  2: (digital communication) pertaining to a transmission technique that requires a common clock signal (a timing reference) between the communicating devices in order to coordinate their transmissions [ant: asynchronous] [1]

  That might be a better starting point than the lay "at the same time" version.

  I believe the real issue is exactly how abstract to get with "same time" so that
  it applies well across the board.  We should be trying real hard to find that sweet
  spot of abstraction, I think.

  An interaction (one-way, two-way, or multi-way) is synchronous if the sender and receiver must communicate at the same time (the reciever must be available to receive the message when the sender sends it). A one-way message is asynchronous if the sender and receiver do not need to communicate at the same time (the message may be stored and delivered at a later time). 

  [wm] I can grasp it intuitively, but there are problems.  First, for there to be "same time",
  there has to be a shared discrete clock, or at least a belief in one.  But then if we look
  at propagation delays (interpreted broadly), it's plain that simultaneous send and receive
  doesn't work.  Maybe it's a nit, but how do you quantify 'close enough'?

  I don't think you do.  I think you step back and realize it's about expectations
  having to do with the clock, but it's definitely NOT about simultaneity in any
  rigorous sense.  ...Which brings us close to the digital communications definition
  cited above, in which the exact application of the clock is left unspecified.

  I'd love to see someone do better, but I doubt it's possible.

  [1] http://dictionary.reference.com/search?q=synchronous


  --Walden