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Re: User agent, Service agent, Client, Server

From: Graham Klyne <GK@dial.pipex.com>
Date: Fri, 30 Jul 1999 11:47:51 +0100
Message-Id: <>
To: Jacob Palme <jpalme@dsv.su.se>
Cc: IETF Applications Area Discussion List <discuss@apps.ietf.org>
At 21:07 29/07/99 +0200, Jacob Palme wrote:
>Is the terminology below correct?
>User agent (UA)     A module which communicates with a user through
>                     a user interface, and performs network operations,
>                     possibly connecting to one or more servers, to
>                     satisfy user requests.
>Service agent (SA)  An agent which performs services, either in the
>                     background or at the request of User Agents.
>Client              A process which opens connections to servers,
>                     and gives commands to them and gets the results.
>Server              A process which accepts connections from clients
>                     and either accepts and performs them, or refuses them.
>Important in the terminology above is the distinction between
>"client" and "user agent". User agents are usually clients, but all
>clients are not user agents.
>If this is the right terminology, what is then the correct word
>for an HTTP server which provides interactive services using
>HTML forms? From an HTTP viewpoint, such a server is a server
>and not a client. But from an application viewpoint, it is a
>user agent. So a user agent can be a server.

Your terminology for "User Agent" tends to cast it in an active role
("performs network services"), which I think would also make it a "client".
 (Similarly, your definition of "service" agent seems to imply a passive

I am reminded of the classic case of the X-window terminal that is also a
"server".  But is it a "User agent"?  I'm dubious (based on your
definitions, it seems not).


Graham Klyne
Received on Friday, 30 July 1999 06:49:52 UTC

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