- From: Mithun Sheshagiri <mits1@cs.umbc.edu>
- Date: Sun, 08 Feb 2004 16:43:18 -0500
- To: Bijan Parsia <bparsia@isr.umd.edu>
- Cc: public-sws-ig@w3.org, skw@hp.com
- Message-ID: <4026AD76.1090109@cs.umbc.edu>
Hello all, Some time back, I wanted to deploy a set of web services which uses RDF/XML for input and output and I essentially adopted the technique suggested by Bijan in his first question. Below is a service that takes in a keyword and returns a list of items that match the keyword. There are certain problems with this approach though. The example service takes in a keyword as an input and produces a list of Items in an ItemList. - keyword - string - ItemList - member - Items Even for such simple class descriptions, the schema is obscenely verbose. I had to embed the schema definitions for keyword and ItemList using the <xsd:choice>. If anyone has a more concise way of describing this thing, please let us all know. Also, it will interesting to see if one could design a tool that takes in class definitions in OWL and convert them into an XML schema. <xsd:schema targetNamespace="http://stuff/IProvider.xsd" <http://stuff/IProvider.xsd> xmlns:xsd="http://www.w3.org/2001/XMLSchema" <http://www.w3.org/2001/XMLSchema> xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" <http://schemas.xmlsoap.org/soap/encoding/> xmlns:effects="http://effects.com/" <http://effects.com/>> <xsd:element name="RDF" targetNamespace="http://www.w3.org/1999/02/22-rdf-syntax-ns#" <http://www.w3.org/1999/02/22-rdf-syntax-ns#>> <xsd:complexType> <xsd:choice> <xsd:element name="ItemList" targetNamespace="http://effects.com/" <http://effects.com/> form="qualified"> <xsd:complexType> <xsd:sequence> <xsd:element name="member" minOccurs="0" maxOccurs="unbounded" targetNamespace="http://effects.com/" <http://effects.com/> form="qualified"> <xsd:complexType> <xsd:attribute ref="rdf:resource" type="xsd:string" form="qualified"/> </xsd:complexType> </xsd:element> </xsd:sequence> <xsd:attribute ref="rdf:ID" type="xsd:string" form="qualified"/> </xsd:complexType> </xsd:element> <xsd:element name="keyword" type="xsd:string" nillable="false" targetNamespace="http://effects.com/" <http://effects.com/> form="qualified"/> </xsd:choice> </xsd:complexType> </xsd:element> </xsd:schema> <message name="ItemLookUp0Request"> <part name="req" element="rdf:RDF"/> </message> <message name="ItemLookUp0Response"> <part name="resp" element="rdf:RDF"/> </message> The service accepts a keyword and outputs ItemList. The SOAP response looks like this: <?xml version="1.0" encoding="UTF-8"?> <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" <http://schemas.xmlsoap.org/soap/envelope/> xmlns:xsd="http://www.w3.org/2001/XMLSchema" <http://www.w3.org/2001/XMLSchema> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" <http://www.w3.org/2001/XMLSchema-instance>> <soapenv:Body> <RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#" <http://www.w3.org/1999/02/22-rdf-syntax-ns#>> <ns2:ItemList ns1:ID="instanceOfItemList" xmlns:ns1="http://www.w3.org/1999/02/22-rdf-syntax-ns#" <http://www.w3.org/1999/02/22-rdf-syntax-ns#> xmlns:ns2="http://effects.com/" <http://effects.com/>> <ns2:member ns1:resource="http://thisone"/ <http://thisone>> <ns2:member ns1:resource="http://thistwo"/ <http://thistwo>> </ns2:ItemList> <ns3:keyword xsi:nil="true" xmlns:ns3="http://effects.com/"/ <http://effects.com/>> </RDF> </soapenv:Body> </soapenv:Envelope> As can be seen, the xml fragment within the <Body> element is valid RDF/XML syntax if one moves the xsi namespace declaration into the RDF element. Incidentally, this message is generated by Apache AXIS and some hacking probably can remove the <keyword> element in the above message altogether. Bijan Parsia wrote: > > Hey folks, > > In WSDL 2.0, an operation is a message exchange pattern (MEP) > instantiated to a set of specific message "types" for each place in > the MEP (with a few other things). The types in question (intuitively) > describe the content of the message (there's some ongoing wrangling > about headers, but, let's ignore them for the moment ;)). > > At the moment, WSDL 2.0 only has built in support for XML Schema > element declarations (as types of messages), and has non-normative > support for DTDs and RELAX-NG. So, there are two issues here: > > 1) Whether to add, normative or not, support for "Semantic Web" type > systems, e.g., OWL and RDFS > 2) How these types should be used to describe messages. > > These correspond, roughly, to additions made to the {types} component > (section 3 or appendix D) and the {message reference} component > (section 2.4). > > (URIs for these sections; > Section 2.4, Message Reference: > http://www.w3.org/TR/wsdl20/#MessageReference_details > Section 3, Types: > http://www.w3.org/TR/wsdl20/#eii-types > Appendix D, Examples of Specifications of Extension Elements for > Alternative Schema Language Support: > http://www.w3.org/TR/wsdl20/#other-schemalang > ) > > Now, I want to put aside the question of normativity for the moment, > mostly because I think there are a series of technical issues that I'd > like to get a better handle on. > > First question: What to (current) semantic web services deployers and > consumers *want*? For some sorts of services, e.g., query or inference > services, it seems like the current proposal is sufficient. If you are > passing in a OWL ontology and expecting to get back entailments, it > makes sense to use an rdf:RDF element for the input and an rdf:RDF > *element* for the output. If you want to use a different serialization > (say, the owl presentation syntax, or the DIG xml syntax) then you > still are passing elements. We might want to distinguish RDF/XML > documents by their owl species (perhaps via mimetype), but, again, > this seems to be solvable with the current system. Non XML > serializations could be handled now by, for example, elements of > simple type, e.g., <n3>:a :b _:c</n3>. (This might be used for > services that covert between RDF/XML and N3.) > > However, in my OWL-S experience, people seem to want to describe the > inputs and outputs (not necessarily the input *messages* and output* > messages) of a services with OWL Classes. I've become a little > confused, in general, as to what that *means*, especially for OWL that > describes non-computational entities, but ok, be that as it may. No, > wait, don't be that as it may. The issue is that in WSDL, the types > describe the messages, and do we want to say that the first input > message to a services is a wordnet:Person? Or do we want to leave > messages (at the WSDL level) described by elements (or simpleTypes) > and layer OWL individuals and classes above that (something similar to > how OWL-S does now)? We think that the industry might not be very interested in services that produce RDF/XML as output; especially the ones who have already deployed web service based systems (that use XML) and have a mature infrastructure for managing and using web services. We probably should look at ways by which semantics could be plugged-in to an existing system. This is also OWL-S position (XSLT templates to convert XML to RDF/XML) as Bijan has mentioned. However, when RDF becomes an houseold name :) , maybe people might be interested in services that produce OWL entailments as the output. regards, mithun > > > Second question: Do we want to deal with the "Decker question"? That > is, what information *must* be passed, and what information *must not* > be passed between services. For example, if I claim that a services > requires a Parent as input, and Parents are Persons, and Persons all > haveParents, how much of the ancestory tree must I pass? (It could get > quite large!) It really depends on the service. Similarly, knowing > that someone is a Parent means that you know that he or she has at > least one child. For some services, you might not need to know > anything more about the children, for others, the actually number of > children is critical, and yet for others, the number and names and > perhaps other information is critical. > > In some distributed systems, this might not be quite a problem. E.g., > in a linda/tuplespace like system, there information may be all shared > (though, still, you might want to know what information a service will > examine *before* you invoke it). In a chatty agent setting, you might > expect the inital message to merely start the conversation, and futher > information to be requested on demand (that still leaves the you might > want to know in advance what will be required, either for efficiency > or privacy). > > It would be nice if we had some means of specifying the information > that must be communicated. Designing such a means is definitely out of > scope of the WDSL group, at least for this go around. It might be > right for some Query group. If, however, what we're passing in > messages is results of queries (for example), then it would seem that > the message's type *isn't* naturally an OWL Class. At least not the > obvious OWL class of "Person". > > ********* > The simplest proposal that might not work is to allow for OWL Classes > (or rdfs, whatever) to be exposed in the Types section as a series of > URIs (do we need non class individuals or properties? We can always > use a nominal singleton class for either, I suppose, though, for the > latter, that'd automatically shove you in owl full), and introduce an > attribute that refers to them. What gets passed over the wire, in a > message, is, by default, the identifier of relevant individual who is > a member of the appropriate class. There is some care needed to > identify by which KB/ontology this individual is known to be of that > class (or, for example, an RDFS agent might send a cat where the > disjoint class of dog was required because it couldn't detect the > contradiction). > > Thoughts, comments, data points? Screams of pain still welcome. > > Cheers, > Bijan Parsia. >
Received on Sunday, 8 February 2004 16:43:34 UTC