[ogsa-wg] Re: latest ws-naming draft (Re: [ogsa-naming-wg] One more thing)

[Mark McKeown]

Hi Frank,
         I have made some comments inline...

First to remove some confusion about IRIs that have appeared in
previous mails in this thread. URNs and URLs are URIs[1], IRIs[2]
are an extension of URIs to support extra charactors. A URI may or may
not map to a real physical address. The WS-Addressing specification[3]
defines a number of URIs that do not map to real network locations
(eg http://www.w3.org/2005/08/addressing/anonymous).
WS-Addressing mandates that the wsa:Address element is an absolute IRI.

>
> * include a profile for the use of the Address and ReferenceParameters
> that ensure the proper uniqueness property in time and space of the
> reference. Tom Maguire suggested to use the wsdl binding of the address
> which sounded very promising.

I am not sure I have understood Tom's argument correctly so I will try and
repeat it here in order to be corrected...

TomM suggested using the wsa::Address as the name, I understand his
argument as being that with the WSDL binding for WS-Addressing you
can include the service part of the WSDL into the wsa:Metadata of the
EPR, the service part may contain a number of network endpoints
indicating that the WS-Resource is available at a number of locations.
>From 'Web Services Addressing 1.0 - WSDL Binding' [4]:

"In particular, embedding a WSDL service component description MAY be
used by EPR issuers to indicate the presence of alternative addresses
and protocol bindings to access the referenced endpoint."

In this case the wsa:Address could be a URN (or URI that is not an
actual network location) and the client could look
to the wsa:Metadata to find the actual network location of the
WS-Resource. Quoting Tom[5]:

"Let me be very clear about this an EPR does not have a 1 to 1
correspondence with a protocol and binding address.  It MUST be
true that an EPR can support multiple protocols and their associated
addresses."

I am not sure I agree, the WS-Addressing WSDL binding uses
"MAY" when discussing including WSDL components in the EPR, there is
no obligation.  I think most services will only use one transport
protocol so I think this feature will not be used often - even if a
service does use more than one transport/port there is no requirement
to advertise this in the EPR. Also there is no transport bindings
available for WS-Addressing - for example the SOAP bindings tells
us to take the wsa:Address element and put it into the wsa:To
element in the SOAP header but does not tell us what to do with it
with regards to the transport protocol (eg most people use
the wsa:Address element to create a RequestURI which they set as the
POST HTTP Header when using HTTP - this issue has been raised with
the W3C TAG[6]).

Quoting WS-Addressing:

"A Web service endpoint is a (referenceable) entity, processor, or
resource to which Web service messages can be addressed. Endpoint
references convey the information needed to address a Web service
endpoint."

To me there is a strong emphasis on singlar.


>
> * include a recipe for generation of a single IRI from the Address and
> ReferenceParameters that can function as an identifier of the resource.
> Mark Mc Keown pointed at the W3C Web Architecture description of the use
> of URIs which we could borrow from.

I am not sure about creating an IRI from the wsa:Address and the
wsa:ReferenceParameters. Consider the following EPRs

<wsa:EndPointReference>
  <wsa:Address>http://grid.org/jobs/4654</wsa:Address>
  <wsa:ReferenceParameters>
       <DateCreated>Thu Nov 17 16:05:43 UTC 2005</DateCreated>
  </wsa:ReferenceParameters>
</wsa:EndPointReference>

and

<wsa:EndPointReference>
  <wsa:Address>http://grid.org/jobs/4654</wsa:Address>
  <wsa:ReferenceParameters>
       <DateCreated>Thu Nov 17 13:07:53 UTC 2005</DateCreated>
  </wsa:ReferenceParameters>
</wsa:EndPointReference>

If DateCreated is just to inform the service when the EPR was created
and is not used by the service for anything else then the two
EPRs are for the same WS-Resource. However if I create a name based
on a combination of the wsa:Address and wsa:ReferenceParameters I will
get two different names, ie I have created URI aliases and divided
the network losing some of the goodness of Metcalfes law [7].

cheers
Mark

[1] http://www.ietf.org/rfc/rfc2396.txt
[2] http://www.ietf.org/rfc/rfc3987.txt
[3] http://www.w3.org/TR/2005/CR-ws-addr-core-20050817/
[4] http://www.w3.org/TR/2005/WD-ws-addr-wsdl-20050413/
[5] http://www-unix.gridforum.org/mail_archive/ogsa-naming-wg/2005/11/msg00021.html
[6] http://www.w3.org/2001/tag/issues.html#endPointRefs-47
[7] http://www.w3.org/TR/webarch/