LC 323 thoughts

For LC 323 http://www.w3.org/2002/ws/desc/5/lc-issues/issues.html#LC323

 

The gist of this was raised at
http://lists.w3.org/Archives/Public/www-ws-desc/2005Aug/0010.html

 

I think that they have a valid point.  The xml media types allow a
notion of "specialization", where media types can be related by
restriction.  In their example, they have two legitimate return media
types that are both +xml, that is sparql-results+xml and rdf+xml.  They
have a single "query" operation and they want to be able to describe
both.  Further, they can have "faults" in multiple media types.

 

I think the crux of the matter is whether we see a URL that returns
multiple media types as conceptually one operation with multiple "return
types" or one operation per media type that are overloaded on one url or
even one operation per input that returns a distinct media type.  I see
pros and cons of these views, but I worry that the one operation
complicates the conceptual view of the binding.  

 

There are 4 solutions that I see:

 

1. Two different query operations that each have their own return media
type and then are deployed at the same url.  As jacek mentioned, query
operation has to fulfill the "operation name mapping" requirement.  I'm
not sure if this would also work for fault media types, but probably.

 

Looking at their scenario, I think that a WSDL author that didn't know
or worry about media types that allowed two different return "types"
would define a different operation for each type, ala "get sparql" and
"get rdf".  Deployed at the same URL, the qname (either rdf or
sparql-results) of the return value will tell them what "they got".  

 

2.   Four different query operations that each have their own return
media type and then are deployed at the same url.  The sparql queries
have well defined rules for which media type will be returned based upon
the input query type.  I *think* they have actually defined about 4
query types.  So they could define 4 operations:

Select returns sparql-results

Ask returns sparql-results

Describe returns rdf+xml

Construct returns rdf+xml 

 

3. force them to return only application/xml

 

4. update WSDL to allow multiple output media types.  

 

To a certain extent, this is about how strong the operation typing is,
ranging from "query in" and "xml out" to "Select input" and
"sparql-out", and if any association between the input and output types
should be in wsdl or not.

 

I think they are effectively asking the WSDL group "How many wsdl
operations are there", and we should provide them an answer.

 

I'll observe that their scenario may be "easy" in that there are a small
# of return type discriminators, and other applications could have a
very large # of discriminators.  

 

Cheers,

Dave