On WSDL attributes


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 07:45:39 UTC