Proposed text for 2.2.21 (take 2)

Based on today's discussions, I've made the following  updates :

1. Removed interaction with pity  :(
2. Removed reference to request and response with pity :(
3. Changed from "a message has zero or more message recipients" to "a
message has one or more message recipients"
4. Clarified that HTTP headers do not support SOAPy features

Questions to ponder:

Do we need to specify the message description language?

Hao
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2.2.21.1 Summary

A message is the basic unit of data sent from one software agent to another
in the context of Web services. 

2.2.21.2 Relationships to other elements

a message is
a unit of data sent from one agent to another

a message may be part of
a message exchange pattern

a message may be described using
a message description language

a message has
a message sender

a message has
one or more message recipients

a message may have
a message identifier

a message may have
a message content

a message may have
zero or more message headers

a message may have
a message envelope

Description

A message represents the data structure passed from its sender to its
recipients.  The structure of message is defined in service descriptions by
a message description language.

A message is defined as a construct that can include zero or more headers,
an envelope, data within the envelope and data external to the envelope. The
header part of a message can include information pertinent to extended Web
services functionality, such as security, transaction context, orchestration
information, message routing information, or management information. The
data part of a message contains the message content or URIs to the actual
data resource.

A message can be as simple as an HTTP GET request, in which the HTTP headers
are the headers and the parameters encoded in the URL are the content. Note
that extended Web services functionality in this architecture is not
supported in HTTP headers.

A message can also simply be a plain XML.  However, such messages do not
support extended Web services functionality defined in this architecture. 

A message can be a SOAP XML, in which the SOAP headers are the headers.
Extended Web services functionality are supported in SOAP headers.