Proposed issue; Visibility of Web services


Last week, a new version of the Web Services Architecture document[1]
was published.  It includes some claims regarding the architectural
property of "visibility"[2], that I believe to be in error.

The relevant text that I disagree with is at the end of Section 1.6.3;

 'The emphasis on messages, rather than on the actions that are caused
  by messages, means that SOAs have good "visibility": trusted third
  parties may inspect the flow of messages and have a good assurance as
  to the services being invoked and the roles of the various parties.
  This, in turn, means that intermediaries, such as fire- walls, are in
  a better situation for performing their functions. A fire- wall can
  look at the message traffic, and at the structure of the message, and
  make predictable and reasonable decisions about security.'


 'In non-REST [Ed. note: or "distributed object" or "mediated" ] but
  XML-based services, the visibility comes from the fact that XML is the
  universal meta-format for the data. Intermediaries can be programmed or
  configured to use the specifics of the SOAP XML format, standardized
  SOAP headers (e.g. for encryption, digital signature exchange, access
  control, etc.), or even generic XPath expressions to make routing,
  filtering, and cacheing decisions. XML-aware firewall and other "edge
  appliance" products are just coming to market as of this writing."'


Note that there have been extensive(!) discussions on this subject on
the Web Services Architecture group's public mailing list, but none of
them were resolved to my satisfaction.  In my view, Web services suffer
from inferior visibility relative to so-called "RESTful Web services",
and even to other systems currently inhabiting the Internet, due to
their non-use of a constrained interface (*any* constrained interface,
not necessarily REST's uniform interface).  The architecture document
should make that clear.



Mark Baker.   Ottawa, Ontario, CANADA.
Web architecture consulting, technical reports, evaluation & analysis
  Actively seeking contract work or employment

Received on Tuesday, 20 May 2003 13:03:16 UTC