The Use of Existing XML Vocabularies for Web Services

1
The Use of Existing XML Vocabularies for Web
Services

• Querying Product Information with Web Services
  and BMEcat

co-authors Dr. Stefan Kuhlins and Ross Tredwell
Universität MannheimLehrstuhl für
Wirtschaftsinformatik IIIkuhlins_at_uni-mannheim.de
Gabriel VöglerDaimlerChrysler Forschungszentrum
UlmSoftware Architekturen (RIC/SA)gabriel.voegle
r_at_daimlerchrysler.com
2
Agenda

• Web Services and electronic price comparisons
• XML vocabularies for product data - BMEcat
• Integration of XML vocabularies in SOAP and WSDL
• Two approaches illustrated using one example
• Procedure-oriented approach
• Document-oriented approach
• Conclusion and Future Directions

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Web Services and electronic price comparisons

• The vision of Dynamic E-Business
• Vision of a fully automatic price comparison
  agent
• Finds all potential suppliers of a certain
  product,
• Queries their electronic catalog,
• Thus determines the best offer.

4
Web Services and electronic price comparisons
(contd.)

• Mapping to Web Service technologies
• All suppliers publish/register their catalog
  service via UDDI
• The agent finds all potential suppliers by
  querying the UDDI yellow pages
• For every supplier
• The agent localizes the WSDL file for the catalog
  service by reading the UDDI green pages
• The agent gets the concrete address of the
  catalog service and generates specific query code
  by looking into the WSDL file
• The agent executes the generated code, which
  queries the catalog service via SOAP
• The agent stores the offer
• The Agent compares all stored offers and thus
  determines the best offer

5
XML vocabularies for product data - BMEcat

• Existing Web Service standards solves the problem
  on the syntactic (technical) level
• Whats about semantics?

6
XML vocabularies for product data - BMEcat
(contd.)

• Several XML vocabularies address the exchange of
  product data (e.g., cXML, xCBL and BMEcat)
• Defined as XML-Schema
• Developed by the industry
• Independent of the transmission method

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XML vocabularies for product data - BMEcat
(contd.)

• BMEcat
• Widespread exchange standard for electronic
  product catalogues in German-speaking countries
• Data Elements
• article master data (part number, abbreviation,
  price and delivery time)
• structural data (product group affiliation,
  product classification)
• additional Information (keywords, references to
  multimedia data)

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Integration of XML vocabularies in SOAP and WSDL

• SOAP can be used as
• Simple transport mechanism for arbitrary XML
• RPC protocol with own type system
• WSDL uses XML Schema to describe messages
  abstractly
• External schemas can be imported
• WSDL guidelines for using XML Schema
• BMEcat does not comply with these guidelines

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Two approaches illustrated using one example

• Example Online Shop
• Classic multi-tier architecture
• Existing web interface has standard possibilities
  for product searches
• Implemented as EJBs, which are invoked by a JSP
  front-end
• Uses a proprietary product model (in terms of a
  Java Bean Product)
• An additional catalog management system allows
  the generation of BMEcat files

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Two approaches illustrated using one example

• Two Approaches to provide a product query Web
  Service
• Procedure-oriented
• SOAP RPC guidelines and encoding rules are used
• The WSDL file uses BMEcat as an abstract message
  description
• Document-oriented
• Only the SOAP messaging framework is used
• The WSDL file uses BMEcat to describe the
  concrete transfer syntax

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Procedure-oriented approach

• Declaration of a WSDL procedure
  lookupDescription() with return type ARTICLE
• a subset of the BMEcat vocabulary is used
• Referencing SOAP encoding rules
• Generation of code skeleton with Service Template
  Generator
• Mapping of proprietary product model to BMEcat
  must be hand coded

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Procedure-oriented approach (contd.)
public generated.bmecat.ARTICLE
lookupDescription(String description) throws
Exception // invoke existing search
implementation de.myCompany.Product
products de.myCompany.shopServer.searchByD
escription(description) // construct BMEcat
types generated.bmecat.ARTICLE articles
new ARTICLEproducts.length // fill
ARTICLE with data of Product for (int i 0
i lt products.length i) articlesi
new de.myCompany.generated.ARTICLE()
articlesi.setSUPPLIER_AID(producti.getProductI
d()) articlesi.getARTICLE_DETAILS.setDESC
RIPTION_SHORT (producti.getDescription()
) articlesi.getARTICLE_PRICE_DETAILS.getA
RTICLE_PRICE .setPRICE_AMOUNT(producti.g
etPrice()) // ... more BMEcat fields
return articles
--gt Uses exisiting Java search methods
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Document-oriented approach

• Declaration of a WSDL procedure
  lookupDescription() with return type BMEcat
• The response contains a complete catalog
  structure
• A few mandatory data elements must be filled with
  dummy data
• No SOAP encoding rules
• Using the BMEcat interface of the catalog
  software
• Implement searchByDescription()with XPath
• No mapping between different data representations
  (Java?XML)
• Result of a query is already in BMEcat and can be
  inserted directly into the SOAP-Body

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Document-oriented approach (contd.)
public SOAPMessage onMessage(SOAPMessage
inMessage) throws Exception //
extract search string from SOAP request
String description inMessage.getSOAPPart(). ...
.getValue() // process XPath query
org.w3c.dom.NodeList resultList
XPathAPI.selectNodes(bmecatDocument,
//ARTICLE....) // generate BMEcat document
for the response org.w3c.dom.Document
bmecatResult ... // fill bmecatResult with
resultLists ARTICLE elements // ... //
generate SOAP response SOAPMessage outMessage
messageFactory.createMessage() SOAPBody
soapBody outMessage.getSOAPPart().getEnvel
ope().getBody() insertDOM(soapBody,
bmecatResult) return outMessage
private void insertDOM(SOAPBody soapBody,
org.w3c.dom.Document document) throws Exception
// inserts a DOM document into the SOAP
body // ...
(other XML APIs)
--gt Uses existing BMEcat catalog
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Conclusion and Future Directions
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Conclusion and Future Directions (contd.)

• Importance of standardized semantics
• Problems with fully automatic Web Service Tools
• Standardization
• Lack of a worldwide accepted standard for product
  description
• Definition of a query interface (search criteria
  and result structure)
• Web-Service bindings for BMEcat