[DAIS-WG] WS-DAI Core WSDL

[Steven Lynden]

Hi,

>> As part of the SemSorGrid4Env project [1], I have been developing a Web
>> service to enable data access to data streams. As a project, we have
>> decided to adopt the WS-DAI standard for data access and define suitable
>> extensions for streaming data.
>
> I am glad to hear this though one slight correction. These specs are
> still officially proposed recommendations. We have just been through
> an interop process that corrected a number of points in GFD.74
> (WS-DAI) and GFD.76 (WS-DAIR). The process and proposed changes are
> outlined in GFD.160 (http://www.ogf.org/documents/GFD.160.pdf).
>
>> However, I have encountered numerous problems in using the WS-DAI
>> Core WSDL specifications [2] with recent Web service frameworks,
>> specifically Axis2 [3] and CXF [4]. The root cause of these problems
>> stems from the use of multiple porttypes in the WS-DAI Core
>> specification, which is not so well supported in these Web service
>> frameworks due to the move to using a single interface for a Web
>> service in WSDL 2.0.
>
> I am sorry to hear this. I'm not the original author of the WSDL/XSD
> and I am no expert in this space so bear with me ...
>
>> Here are some specific questions:
>>  1. Have other developers, e.g. the OGSA-DAI team, encountered such
>>     issues and how have they resolved them? Also, are there plans on
>>     moving the OGSA-DAI software to use a more recent Web service
>>     framework than Axis [5]?
>
> Mike already answered this.
>
>>  2. Are there plans to update the WS-DAI standards, specifically to use
>>     WSDL 2.0 with its single interface declaration per service?
>
> Not at the moment. However, if you like to help do this we could
> possibly take it on if the other group members think that this would
> be a worthwhile thing to do.

I think its worthwhile, especially if it gets more people
involved/interested. On a related note there is some interest in a
RESTful profile/bindings, discussed last year on this list.

> Is it possible for a client to
> interoperate with a WSDL 1.1 and a 2.0 service or is this not
> possible? Are the two message types specified in the WSDL compatible
> at all?
>
>>  3. Why does the WS-DAI Core specification WSDL not declare the
>>     GenericQueryFactory operation in the same way that it has a
>>     GenericQuery operation?
>
> You mean why does it not declare it at all? The core spec only
> proposed a set of patterns to be adopted by extensions to the core
> spec. At the time I think it was thought that that would become the
> responsibility of the extensions to particular data models as indeed
> has become the case. In the interop process it became somewhat
> superfluous to use Generic Query when there were more suitable
> alternatives from the Relational spec. In a context where a service
> might operate with a more diverse type of data this might be a nice
> way to generically access data. As for the GenericQueryFactory as far
> as I recollect the rationale, as I said, was that the core spec would
> infer the message exchange pattern and it would be up to the
> realisations to actually implement it.

One reason could be that if you implemented a GenericQueryFactory
operation and created a new resource the only thing that you could
describe it with using the core specification would be the basic
DataResourceDescription. Probably you would want to extend that in
order to describe the characteristics of the new resource. If it was
extended you would be defining a new type of resource and the correct
place for that would be in an extension of the core spec such as
WS-DAIR or WS-DAIX etc. GenericQuery is defined without any
assumptions about the way it is used (including use of factory
patterns), you can send any type of query and get anything back. As
Mario said its usefulness was debated during the interop process. Do
you envisage using it?

> I think these are partial answers but if you are willing to enter a
> dialogue can try to substantiate these matters. I also welcome any
> input from my colleagues who might have a point of view.
>
> Mario
>
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> |Mario Antonioletti:EPCC,JCMB,The King's Buildings,Edinburgh EH9 3JZ.   |
> |Tel:0131 650 5141|mario at epcc.ed.ac.uk|http://www.epcc.ed.ac.uk/~mario/ |
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Steven.