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Re: Compendium of "synchronous" definitions

From: Francis McCabe <fgm@fla.fujitsu.com>
Date: Mon, 3 Mar 2003 09:10:24 -0800
Cc: www-ws-arch@w3.org
To: "David Booth" <dbooth@w3.org>
Message-Id: <05F781DC-4D9B-11D7-B6EA-000393A3327C@fla.fujitsu.com>

   I would appreciate it if you could add mine to the long list:

a straightforward definition of synchronous:

A rendezvous of two activities is synchronous if they complete 

The language, if not the definition, comes from Communicating 
Sequential Processes.

One might try to sharpen this up by defining simultaneously in terms of 
clocks etc. But that is not necessary; because an alternative view of 
this definition is:

An activity involved in a synchronous rendezvous may assume that the 
rendezvous is complete for both sides if it 's side completes.


On Thursday, February 27, 2003, at 04:58  PM, David Booth wrote:

> Here are the proposed definitions of "synchronous" that I've collected 
> from the list.  If I've missed any, it was only due to volume of 
> messages I was trying to sort through -- not due to any desire to 
> slight anyone -- so please accept my apology.  If that happened, and 
> you do feel that (yet) another definition should be considered, please 
> re-submit it to the list by reply message and give it a unique name as 
> I've done with the others below, so that we can be clear when in 
> referring to them.
>          ==============================================
> Definition dbooth-2
> [This is my attempt at combining the main concepts I've seen in 
> others.]
> Synchronous interaction
> An interaction is synchronous if the parties are involved in the 
> interaction at the same time and the interaction carries an 
> expectation of immediate processing.  A one-way interaction is 
> synchronous if successful message delivery implies that the message 
> either has been processed by the receiver or is actively being 
> processed.  A round-trip or more complex interaction is synchronous if 
> the initiator pauses some of its processing to wait for the 
> interaction's constituent messages to be processed.  In a round-trip 
> interaction, the request and response are often sent over the same 
> communication channel.
> ----
> Definition dbooth-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0222.html
> Property of an interaction whose results are directly following the 
> interaction. An interaction between an initiator and a respondent is 
> synchronous if the initiator blocks some further processing while it 
> waits for a corresponding action, response or acknowledgement from the 
> respondent.
> ----
> Definition ugo-2c
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0386.html
> Asynchronous: A request/response interaction is said to be 
> asynchronous when the request and response are chronologically 
> decoupled. In other words, the client agent does not have to "wait" 
> for the response once it issues the initial request. The exact meaning 
> of "not having to wait" depends on the characteristics of the client 
> agent (including the transfer protocol it uses). Examples include 
> receiving the response on a different thread, on a different socket, 
> on a different end-point, by polling the server, etc.
> Synchronous: The opposite of asynchronous.
> ----
> Definition daveo-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0432.html
> synchronous
> a programmatic flow of control on the sender effectively does nothing 
> but wait for a response after sending it's request
> ----
> Definition daveo-2
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0432.html
> synchronous
> the request and response flow forwards and backwards over the same 
> virtual connection between the sender and receiver.
> ----
> Definition moberg-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0343.html
> A web service response is said to be synchronous iff it is returned 
> using the same network connection used in sending the request to which 
> it is a response. (This implies that only one URL would be needed for 
> request-response MEP when the response is synchronous and uses a 
> transfer protocol that has URLs. It also implies that the request and 
> response occur within the interval of time that the network connection 
> exists. Also, there is overhead in setting up only one TCP connection 
> when TCP is used, and since we are talking about IP _connections_ that 
> will be almost always the case.)
> A web service response is said to asynchronous iff it is returned 
> using a network connection that is distinct from that used for sending 
> the request to which it is a response. (Implications: Two URLs are 
> needed to configure a request-response MEP when the response is 
> ==>asynchronous. The response connection may occur while the request 
> connection is still open or after it is closed. For TCP-based transfer 
> protocols, two connection setups will be needed.)
> ----
> Definition assaf-3
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0354.html
> A transport is synchronous iff the request is returned using the same 
> network connection.
> ----
> Definition cutler-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0358.html
> Synchronous: a request/response exchange that is correlated by virtue 
> of a serialized, sequenced exchange of messages between requestor and 
> respondant, typically over the same socket or stream.
> Asynchronous: a request/response exchange that is not synchronous, 
> typically relying on some mechanism such as Message-ID within the 
> messages to correlate the request and response messages.
> ----
> Definition ferris-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0437.html
> synchronous message exchange (applies to oneway as well as 
> request/response) requires that both sender and receiver, or initiator 
> and respondant, processes are running/active at the same time as the 
> exchange takes place. In the case of request/response, the exchange is 
> synchronous if both sender and receiver remain in the running/active 
> state for both the request and response.
> asynchronous message exchange (also applies to oneway or request 
> response) does not require, but does not preclude, that both sender 
> and receiver, or initiator and respondant, processes are 
> running/active at the same time as the exchange takes place. It 
> typcally requires some form of mediation between the sender and 
> receiver such as a message queue.
> ----
> Definition mikec-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0318.html
> (Taken from 
> http://whatis.techtarget.com/definition/0,,sid9_gci213080,00.html ?)
> In program-to-program communication, synchronous communication 
> requires that each end of an exchange of communication respond in turn 
> without initiating a new communication. A typical activity that might 
> use a synchronous protocol would be a transmission of files from one 
> point to another. As each transmission is received, a response is 
> returned indicating success or the need to resend. Each successive 
> transmission of data requires a response to the previous transmission 
> before a new one can be initiated. Synchronous program communication 
> is contrasted with asynchronous program communication.
> ----
> Definition walden-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0326.html
> Synchronous, then, places a constraint on a response such that the 
> response must be received within a strictly or loosely defined time 
> quantum (strict vs lax synchrony), or else the exchange fails.
> Asynchronous differs in that no amount of elapsed time signals the 
> failure of the exchange.
> ----
> Definition assaf-1
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0321.html
> An operation is synchronous if both service requester and service 
> provider
> engage will always engage in that operation at the same time.
> ----
> Definition assaf-2
> http://lists.w3.org/Archives/Public/www-ws-arch/2003Feb/0321.html
> An interaction is synchronous if activities demarcated by that 
> interaction
> will always be performed at the same time.
> -- 
> David Booth
> W3C Fellow / Hewlett-Packard
> Telephone: +1.617.253.1273
Received on Monday, 3 March 2003 12:11:37 UTC

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