SPARQL Annotations in WSDL

Simple/practical linkages of web services.

Eric Prud'hommeaux, Sanitation Engineer.
Last modified: $Date: 2010/12/06 16:10:09 $

This work is licensed under a Creative Commons Attribution 3.0 License, with attribution to W3C.

WS2: Work Package 2

Annotated Service Invocation

Execute (services described by) WSDL interfaces to answer user queries.

Procedure

Identify the information in web services.
- annotate existing descriptions

Query that specific information.

SELECT ?asin ?title WHERE {
_:b tns:id "0FWYBWB91M5S26YBE382" ;
    tns:keywords "Weaving" ;
    tns:index "Books" ;

    tns:asin ?asin ;
    tns:title ?title ;
    tns:page ?page }

Automatically invoke the appropriate service(s).

Features

Modeled operations' inputs and outputs as rules.
Modeled parameters in user query as ground facts.
Choreography!
Separate documentation for SPARQL Anntoations and SPARQL Annotations on WSDL.

Features of SPARQL in WSDL (SPDL)

Annotations on web service operations
Builds RDF graph query pattern
Uses (relatively familiar) SPARQL query pattern
— Sufficient for invocation given a grounding for the pattern

Connecting SPARQL to XML

  <ItemAttributes>
     <Title>Learning to Weave, Revised Edition</Title>   
     <Author>Deborah Chandler</Author>                   
     <Author>Debbie Redding</Author>                     
  </ItemAttributes>

  <xs:element name="Item">
    <xs:complexType spat:SPAT='?book tns:doctitle xpath("aws:Title")...'>
      <xs:sequence>
	<xs:element name="Title" type="xs:string" minOccurs="0"/>
	<xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

Identifying information

Using SPARQL Annotations (SPARQL + XPath) in WSDL:

SPARQL: SQL-like RDF query language

SELECT ?tile WHERE { ?response tnss:doctitle ?title }

XPath: identify locations in a document

aws:ItemSearchResponse/aws:Items/aws:Item/aws:Title

WSDL/XSD: associate messages (documents) with services

<definitions><types><element name="ItemSearchResponse"></element></types>...
    <message name="ItemSearchResponseMsg"/></definitions>

SPARQL annotations tie RDF data to locations in a Web Services message.

<xs:element name="Item" spat:SPAT='?book tns:doctitle xpath("aws:Title")'/>

Demo excerpts

PREFIX tnss: <http://webservices.amazon.com/AWSECommerceService/2004-11-10>
SELECT ?title ?page WHERE {
_:b tnss:id "0FWYBWB91M5S26YBE382" ;
    tnss:keywords "Weaving" ;
    tnss:index "Books" ;

    tnss:asin ?asin ;
    tnss:doctitle ?title ;
    tns:page ?page }

title	page
"Learning to Weave, Revised Edition"	"http://...ASIN=1883010039..."
"Weaving Music into Young Minds with Education (Weaving Music Into Young Minds With Education)"	"http://...ASIN=0766800199..."
"Spin to Knit: The Knitter's Guide to Making Yarn"	"http://...ASIN=1596680075"

SAWSDL Specification

Semantic Annotations for WSDL and XML Schema
- W3C Candidate Recommendation
- Defines:
  - modelReference: association between a WSDL entity and a concept in some semantic model
    - XSD complex types, simple types, elements, and attributes
    - WSDL operations and interfaces
  - liftingSchemaMapping and loweringSchemaMapping;, transformation of information from Web Service messages to semantic model
    - XSD elements, complex types and simple types

SAWSDL Specification

Accompanying Usage Guide references:
- SPARQL Anntoations
- SPARQL Annotations on WSDL
and describes their use in SAWSDL.

SPDL Expressed in SAWSDL

a sawsdl:loweringSchemaMapping:

      <xs:element name="Item">
        <!-- xs:complexType spat:SPAT='?book tns:doctitle xpath("aws:Title") -->
        <xs:complexType sawsdl:loweringSchemaMapping='&AWS;title'>
	  <xs:sequence>
	    <xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
	    <xs:element name="Title" type="xs:string" minOccurs="0"/>
	  </xs:sequence>
	</xs:complexType>
      </xs:element>

points to a document containing the SPDL annotations:

:id       spat:SPAT '?req :id xpath(".")' .
:keywords spat:SPAT '?req :keywords xpath("tns:Keywords") ; :index    xpath("tns:SearchIndex")' .
:asin     spat:SPAT '?book :asin xpath("tns:ASIN")' .
:title    spat:SPAT '?book tns:docTitle xpath("aws:Title")' .

Operation Rules

Model information in Input and Output as a graph pattern.
Allow engine to infer service invocation paths.

Very simple inference appears to model reasonable use cases.

Rule Construction Details

Traverse operation input and output:

    <operation name="ItemSearch">
      <input message="tns:ItemSearchRequestMsg"/>
      <output message="tns:ItemSearchResponseMsg"/>
    </operation>

for the annotations:

    <xs:element name="ItemSearch"
     spat:SPAT='?req tns:asin xpath("tns:ASIN")'>
        ...
          <xs:element name="ASIN" type="xs:string" minOccurs="0"/>
        ...
    </xs:element>

Build rule from rule body (Input) and rule head (Output):

┌ op {http://webservices.amazon.com/AWSECommerceService/2004-11-10}ItemLookup: 
│     fwrule ask(?req this:id XPath(., 91642dc) && 
│                ?req this:asin XPath(., 919d638))
│            assert(?req this:page _:<>:8.XPath(this:Items/this:Item/this:DetailPageURL, 91d37c8) && 
│                   ?req this:reqId _:<>:9.XPath(., 9211c38) && 
│                   ?req this:asin _:<>:10.XPath(tns:ASIN, 920b2b0) && 
│                   ?req this:title _:<>:11.XPath(tns:Title, 9298a50))
│               -->{<qname:{http://webservices.amazon.com/AWSECommerceService/2004-11-10}ItemLookup>}

Rule Invocation Details

The ground facts from the users query:

PREFIX tns: <http://dev.w3.org/cvsweb/perl/modules/W3C/SPDL/descriptions/AWSECommerceService-SAWSDL-item-terms.ttl#>
SELECT ?title ?page WHERE {
_:b tns:id "0FWYBWB91M5S26YBE382" ;
    tns:keywords "Weaving" ;
    tns:index "Books" ... }

combined with a rule head:

┌ op {AWS:ItemSearch: 
│     fwrule ask(?req this:id XPath(., 8ae97f0) && 
│                ?req this:keywords XPath(tns:Keywords, 91b1d40) && 
│                ?req this:index XPath(tns:SearchIndex, 91b1d40))
│            assert(?req this:reqId _:19.XPath(., 92b17b0) && 
│                   ?req this:asin _:20.XPath(tns:ASIN, 92d6890) && 
│                   ?req this:title _:21.XPath(tns:Title, 93150e0))
│               -->{AWS:ItemSearch}

produce new inferences:

_:21 this:reqId _:19.XPath(., 92b17b0) .
_:21 this:asin _:20.XPath(tns:ASIN, 92d6890) .
_:21 this:title _:21.XPath(tns:Title, 93150e0) .

Rule Combination Details

The produce of one inference:

_:21 this:reqId _:19.XPath(., 92b17b0) .
_:21 this:asin _:20.XPath(tns:ASIN, 92d6890) .
_:21 this:title _:21.XPath(tns:Title, 93150e0) .

combined with another rule head:

┌ op {AWS:ItemLookup: 
│     fwrule ask(?req this:id XPath(., 91b1548) && 
│                ?req this:asin XPath(., 920be4c))
│            assert(?req this:page _:8.XPath(tns:Items/tns:Item/tns:DetailPageURL, 9127a6c) && 
│                   ?req this:reqId _:9.XPath(., 92b17b0) && 
│                   ?req this:asin _:10.XPath(tns:ASIN, 92d6890) && 
│                   ?req this:title _:11.XPath(tns:Title, 93150e0))
│               -->{AWS:ItemLookup}

produces new inferences:

_:22  this:page   _:8.XPath(this:Items/this:Item/this:DetailPageURL, 91d37c8) .
_:22  this:reqId  _:9.XPath(., 9211c38) .
_:22  this:asin   _:10.XPath(tns:ASIN, 920b2b0) .
_:22  this:title  _:11.XPath(tns:Title, 9298a50) .

Querying Rule Closure

The closure of the rules is now useful for answering user queries:

PREFIX tnss: <http://webservices.amazon.com/AWSECommerceService/2004-11-10>
SELECT ?title ?page WHERE {
_:b tnss:id "0FWYBWB91M5S26YBE382" ;
    tnss:keywords "Weaving" ;
    tnss:index "Books" ;

    tnss:asin ?asin ;
    tnss:doctitle ?title ;
    tns:page ?page }

title	page	_:b	asin
XPath(tns:Title)	XPath(...PageURL)	_:22	_:20.XPath(tns:ASIN)
XPath(tns:Title)	XPath(...PageURL)	_:22	_:10.XPath(tns:ASIN)

Studying Proof Chain

The proofs of these rules illustrate how to invoke the services:

_:22 this:page XPath(...PageURL) .

-->{

[

fwrule ask(?req this:id XPath(.) && ?req this:asin XPath(.)) assert(?req this:page XPath(...PageURL) && ?req this:reqId _:9.XPath(.) && ?req this:asin _:10.XPath(tns:ASIN) && ?req this:title _:11.XPath(tns:Title)) -->{AWSECommerceService:ItemLookup}

_:22 this:asin _:20.XPath(tns:ASIN) .

-->{

[

fwrule ask(?req this:id XPath(.) && ?req this:keywords XPath(tns:Keywords) && ?req this:index XPath(tns:SearchIndex)) assert(?req this:reqId _:19.XPath(.) && ?req this:asin _:20.XPath(tns:ASIN) && ?req this:title XPath(tns:Title)) -->{AWSECommerceService:ItemSearch}

_:22 this:index "Books" .

-->{<>}

_:22 this:id "0FWYBWB91M5S26YBE382" .

-->{<>}

_:22 this:keywords "Weaving" .

-->{<>}

]

}

_:22 this:id "0FWYBWB91M5S26YBE382" .

-->{<>}

]

}

Invoking Rule Services

Base Rules (inner-most nesting) are prooven by ground facts in the query.
These are executed first.
Dependent Rules use, at least in part, the product of these executions.
These solutions produced by executing the queries replace the original solutions.

Documentation

SPARQL Annotations on WSDL describes the strategy.
AWS Choreography Example shows the working details.

Conclusions

The SPDL annotations for AWS:ItemSearch are sufficient to execute example queries.
The demonstrator is able to use that information to invoke operations in the correct order.
Minimal annotation is required for automatic invocation.
Only minimal inference required.

Future Work

There's always more to play with...

Backward chaining.
Apply to NIH services.
Many potential features to add...

Questions/Discussion

Impressions of the demonstrator.

Applicability to industry today and tomorrow.

Applicability to users today and tomorrow.

data flow/process details