Description Framework (RDF) model and syntax Information Semantic Web Languages: RDF vs. SOAP Serialisation Stefan Haustein haustein@ls8.cs.uni-dortmund.de 0 University of Dortmund , Computer Science VIII, D-44221 Dortmund , Germany 1999 1 8

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1. INTRODUCTION 2. RDF EVOLUTION 3. RDF SYNTAX ISSUES

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Semantic Web Workshop 2001 Hongkong, China

Copyright by the authors. </ApDescription> </transportProfile> <dynamic>true</dynamic> <mobility>true</mobility> <name>paris.agentcities.org</name> <ApDescription id="1"> <transportProfile> <MtpDescription id="3"> <rdf:Bag> </addresses> <addresses> <mtpName>fipa.mts.mtp.iiop.std</mtpName> <rdf:li>iiop://leap.crm-paris.com:9000/paris.agentcities.org/acc</rdf:li> </rdf:Bag> <rdf:li>iiopname://leap.crm-paris.com:9000/paris.agentcities.org/acc</rdf:li> </MtpDescription> </rdf:li> <rdf:li> </rdf:li> </rdf:Bag> </availableMtps> </ApTransportDescription> <availableMtps> <ApTransportDescription id="2"> <rdf:li> <rdf:Bag> <rdf:li>http://leap.crm-paris.com:8080/acc</rdf:li> </MtpDescription> </addresses> <addresses> </rdf:Bag> <rdf:Bag> <mtpName>fipa.mts.mtp.http.std</mtpName> <MtpDescription id="4"> rdfs:Class

rdf:type rdf:type rdfs:ressource rdfs:subclassOf rdfs:subclassOf

ApDescription ApTransportDescription

MtpDescription domain domain range domain domain domain name dynamic transportdescription range rdf:type

rdf:type rdf:type availableMtps mtpName profile addresses rdf:type

rdfs:Property rdf:type

Literal range range rdfs:Bag required in RDF. source of statements: The source information would be atown schema language. Instead, XML Schema is used for validation of the syntactical correctness of SOAP serialised propriate for modelling ontologies. tached to just one object instead of needing reication for a level of ontology modelling, SOAP serialisation ts w ell into building blocks may have advantages e.g. when tracking the to RDFS, there is no signican t dierence. Larger basic RDF. And when comparing the RDFS and UML diagrams OIDs, it becomes very simple to make statements about more complex than plain RDF. However, when compared (gure 3 and gure 2), UML seems signican tly more apobjects. While XML Schema does not seem the appropriate lot of RDF statements. Also, when constructing URLs from properties and a type. Thus, the basic building blocks are UML modelling without the property naming problems of The SOAP Data Model consists of structured objects having statements, again avoiding explicit reication that w ould be SOAP is based on a simple object oriented data model.

In contrast to RDF, SOAP does not come along with its

5.1 SOAP and CORBA like weather forecasts, trac services, or logistics coordinaIn his WWW9 presentation, Henrik Frystyk Nielsen ([ 16 ]) HTML, SOAP is dened for direct comm unication between possible future scenarios in the areas where \Semantic Web" serialisation syntax. While he states in his presentation that SOAP is not meant to replace RDF, this is clearly one of the can SOAP be integrated into the Semantic Web? Can the Web in many ways or even become a signican t part of it. tion. Although SOAP supports alternative content formats, means exchange of information that is machine readable in it is likely that most of the content will actually be encoded the rst place.

Semantic Web prot from SO AP services? ming languages (C++, Java, Perl, . In contrast to Python)2 a Semantic Web that is widely accepted and used. SOAP using SOAP serialisation. Thus, some questions arise: How Implementations are available for a wide range of programmachines over the Internet, so it may aect the Seman tic SOAP is suitable for all kinds of automated Internet services demonstrated how RDF can be encoded utilising the SOAP 5.2 SOAP Syntax 5.3 SOAP Data Model 6. IS SOAP SUITABLE FOR THE SEMAN

TIC WEB? 6.1 Using SOAP Syntax for the RDF Data Model by Henrik Frystyk Nielsen [ 16 ]. say \something" about a given URL. However, it seems relEven if a \standard" object-oriented data model is suitinside that object. So, in order to be able to say anything While for object oriented systems it is true that property In [2], Tim Berners-Lee justies the usage of the propert yis intended to describe a resource, it could have an \about" So there is no real requirement that e.g. the PICS rating that objects cannot hold information about other objects. information is stored with the objects, this does not mean able for the Semantic Web, there is still a problem with object and its description stored at an insurance company. centric data model instead of an \usual" object-oriented erally assume that information about an object is stored A more complex example could be a car being the primary vice address and a local unique number (OID). If an object property like in the SOAP-encoded RDF syntax proposed sign URLs to objects. There is also no general mechanism to about anything, it becomes necessary to store the properties SOAP. The SOAP specication does not specify ho w to asapart from the object. be a separate object holding a pointer to the original page. of an HTML page is a property of that page. It could also data model by claiming that object-oriented systems genatively simple to assign URLs to objects built from the ser6.2 Saying Anything about Anything 6.3 Schema Language 6.4 Integration of existing Services and Systems was already discussed for XSLT and UML, but we also have ject Data Management Group (ODMG) ts perfectly with XML DTD or XML Schema, it would be sucien t to agree for XML languages designed \by hand". a well designed query language for object oriented systems.

Another SOAP advantage is that SOAP quite nicely inof abstraction. schema generation process. Instead of needing to design an SOAP and preserves a high degree of SQL compatibility.

Moreover, since SOAP ts nicely in to existing object oriented and relational database systems, it may simplify the tegrates with a lot of existing standards (Table 1). This The Object Query Language (OQL) [7], designed by the Obon an UML diagram, allowing a much more appropriate level

Also, mechanisms for schema translations may become

looking at existing inference systems, it does not seem more For a real \Semantic Web", the upper logical levels are necessary. For example, if a legacy system with a direct SOAP mapping needs to be adapted to a SOAP based standicult to build them for SO AP than for RDF [13]. missing from SOAP. But this holds for RDF as well, and to interoperate. However, this will probably be more simple than general XML-XML translations, where XML-XML translations are possible today using XSLT. Again, the same dard, or if SOAP based standards for dieren t areas need would be necessary for RDF.

 For the future, it seems to make sense to work on both

dieren t than annotation of existing pages with additional tion in the rst place. So, in contrast to RDF, an extra SOAP may split the Semantic Web community to some exa clear and simple syntax. The SOAP Serialisation syntax and SOAP may allow for an integration of both approaches conversion step can be avoided completely.

Although SOAP is not suitable for \in place" annotation in order to become really suitable for the Semantic Web, it are similar to some extent, and both are relevant for the dicult to translate in to each other. approaches without dooming the other. Even if looking at meta data. The main problem is that both approaches are tend, competition may also set free a lot of development about anything", RDF uses URLs as global unique identiIn contrast to SOAP, RDF is suitable for \in place" annoThe logical level is not yet covered for both approaches, tation of existing web pages. For being able to say \anything \Semantic Web", especially when the term means something ers. nearly reaches the quality of a \hand-made" one. Thus, at some future point of time. and would require an extension assigning URLs to objects into other standards like UML, XSLT and OQL. It provides RDF and SOAP. energy. Perhaps the logical layer to be built on top of RDF has several advantages in other areas. SOAP ts quite w ell SOAP serialisation is suitable as content encoding convenObviously, we have two formats and data structures that 7. WHAT IS MISSING 8. CONCLUSION

 Workshop on Intelligent Information Integration, 1999 . knowledge representation for the web . In IJCAI'99 Web. In WWW9 , 2000 . rdf/protege-rdf- 20000629 .html. [18] Stanford University. Using Protege-2000 to Edit RDF , [19] Frank van Harmelen and Dieter Fensel . Practical Language Specic ation , June 1999 . Version 1.3. June 2000 . http://www.smi.stanford.edu/projects/protege/protege- [16] Henrik Frystyk Nielsen . Soap, RDF and the Semantic [17] Object Management Group. OMG Unie d Modeling