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Re: On WSDL attributes

From: Steve Graham <sggraham@us.ibm.com>
Date: Tue, 9 Sep 2003 08:03:01 -0400
To: "Savas Parastatidis" <Savas.Parastatidis@newcastle.ac.uk>
Cc: "WS Description List" <www-ws-desc@w3.org>, www-ws-desc-request@w3.org, public-ws-desc-state@w3.org
Message-ID: <OF221E858A.FD2AE3AB-ON85256D9C.00414CBA@us.ibm.com>

We continue to debate the merits for this work.  We have constituencies in
the Systems Management space (OASIS WSDM TC) and Grid (OGSI) that clearly
need the notion of attributes in WSDL.  We do not believe the concept is
limited to those two domains, the concept is much broader than that.

We agree that a Web service fundamentally is about message exchanges.  The
attribute work defines additional information that helps the requestor form
these messages, by indicating what sort of information can be the subject
of the get and set operations. Furthermore, it does this in such a way that
allows more powerful interfaces (such as OGSI service data operations) to
be defined to reuse the base information provided by the attribute
declaration mechanism.

You claim that attributes are not a concept in the WSA.  However it is true
that they are not FORBIDDEN by WSA.  This extension is needed for Grid and
Systems management, and may be quite useful in other spaces.  BPEL has
properties for example, that appear to be a similar concept, would it not
be better if  we all used the same mechanisms for properties/attributes
etc? We agree that attributes in WSDL does not exist, we are proposing,
based on our experience in Grid and Systems management that it be added.

The notion that the work in MEPs is sufficient and precludes the work for
attributes is misguided.  We proposed some simple access mechanisms to
suggest how bindings treat attributes in an analogous way to operations.
The MEPs work does not reduce the need for attributes.

We continue to disagree about the relationship between objects and SOA.
Object orientation is an implementation concept.  There is nothing in SOA
that precludes an object-orientation or a non-object orientation.

Of course, we could always use extensibility to support attributes, in fact
this what OGSI does today with serviceData.  However, it was deemed
appropriate, by several constituencies to try to standardize attributes in
the core language.


Steve Graham
(919)254-0615 (T/L 444)
STSM, On Demand Architecture

                      "Savas Parastatidis"                                                                                                     
                      <Savas.Parastatidis@newca        To:       "WS Description List" <www-ws-desc@w3.org>                                    
                      stle.ac.uk>                      cc:                                                                                     
                      Sent by:                         Subject:  On WSDL attributes                                                            
                      09/09/2003 07:43 AM                                                                                                      


Here are some thoughts by Jim Webber and myself on the introduction of
attributes in WSDL...

The proposal on the introduction of attributes in the WSDL specification
has come a long way due to the work that the relevant Task Force has
produced. The most recent update to the proposal is, we believe, closer
to the WSDL way of describing message exchanges. However, it is so close
that we believe attributes are not necessary for WSDL.

1. Attributes represent a concept that it is not part of the Web
Services Architecture. Nowhere in the WSA document, to our knowledge, is
it suggested that a Web Service has attributes. Web Services send and
receive messages. They do not have operations, functions, methods, or
attributes as it is the case with object-based component models. WSDL is
used to describe messages that can be sent and received. The notion of
an "attribute" attempts to add a characteristic to Web Services that
simply does not exist.

2. The current version of the proposal defines particular message
exchange patterns. Since there is already work being carried out in this
area, we feel that there is no need for the introduction of attributes
in WSDL. For instance, the notion of a solicit-response MEP is somewhat
analogous to "getting" an attribute, while a request-only MEP is
analogous to "setting" an attribute. Given these abilities which are
already an accepted part of WSDL, this undermines the need for "read",
"read-write", and "write" qualifiers for attributes.

To summarise: We believe that attributes are a fundamental property of
object-based systems, and do not have a corresponding use in SOA. We are
supported by WSA in this thinking. Furthermore, we believe that the
benefits of an attribute style interaction in terms of being able to
"set" or "get" structured XML data from a Web service is already
supported with WSDL operations.

While we think that the work of the ATF is correct in itself, we would
oppose the inclusion of such work into WSDL, and would instead
anticipate that it would form part of some other specification which
leverages WSDL extensibility. Those communities which have a
demonstrated need to deploy Web services in a distributed object-like
scenario (e.g. Grid), can then utilise the separate attribute
specification to support their needs, without adding non-WSA features to

Jim Webber
Savas Parastatidis
Received on Tuesday, 9 September 2003 08:08:29 UTC

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