Semantic Web Languages: RDF vs. SOAP Serialisation
Stefan Haustein University of Dortmund, Computer Science VIII, D-44221 Dortmund, Germany
AP just as a syntax enco ding of the
ABSTRACT gestion is not to use SO
RDF data mo del but to build a part of the Semantic Web
Although RDF is considered the Semantic Web language,
on SOAP serialisati on in the rst place.
it may not b e the only one. SOAP serialisati on provides
several advantages, esp ecially if the Semantic Web is not
viding meta data for existing web pages, but
just ab out pro 2. RDF EVOLUTION
also ab out exchange of content that is machine-readabl e in
The Resource Description Framework RDF [15] was
the rst place. This pap er discusses some problems with
originall y designed by the World Wide Web Consortium
the RDF syntax and data mo del. RDF is compared to
W3C as a meta-language for annotating existing web pages
SOAP, and some SOAP advantages like b etter integration
with additional machine-readable information. Atypical
with existing standards and systems, improved readability,
RDF applicatio n is the Platform for Internet Content Se-
and industry supp ort are p ointed out.
lection PICS [6], that is intended to annotate existing web
resources with meta-data ab out e.g. the suitabili ty of the
Keywords: SOAP Serialisati on, RDF, RDFS, Ob ject-
content for children.
Orientation
Although RDF was originally designed for annotation of
existing web pages only, it is currently widely considered
hine-readable format for the Semantic Web and the
1. INTRODUCTION as mac
DARPA Agent Meta Language DAML .
What are the consequences if the term \Semantic Web"
However, when using RDF as the primary information
do es not just mean HTML with some meta-data, but also
format, and not just for meta data annotation, some issues
content that is machine-readable in the rst place, thus b e-
arise. These problems are describ ed in detail in the following
ing suitable for application s like software agent communica-
sections. For an overview of additional general RDF issues
tion? Although RDF is suitable for that purp ose, its syntax
and inconsistencies , the reader is referred to [4] and [10].
and data mo del are clearly optimised for annotating exist-
ing do cuments with meta data, describing existing web re- hine readable format.
sources using a mac 3. RDF SYNTAX ISSUES
In contrast to HTML, the exibili ty of XML allows stor-
The requirement that RDF should b e usable for annotat-
ing all relevant meta data in a machine-readable format
ing existing pages with meta-data without breaking browser
in the rst place. With the increasing separation of content
compatibili ty for the actual content resulted in a syntax that
and layout into XML and XSLT les, and the dynamic gen-
is more complicated than necessary for plain RDF do cu-
eration of X HTML, the need for a separate meta mo del
ments. Also, several alternative syntax forms exist. All
may decrease. Naturally, RDF is well suited for annotat-
alternatives are semantically equivalent, but have di erent
ing the generated HTML with information like PICS, but is
e ects on the rendering pro cess in the browser that is used
content annotation really all the Semantic Web is ab out?
to view the do cument.
This article discusses some serious issues concerning the
The general RDF syntax consists of simple resource de-
RDF syntax and data mo del when used as a primary ma-
scriptions \prop erties" emb edded in a \description" ele-
chine readable content format, instead of just adding meta-
ment. In order to illustrate RDF and SOAP syntax alterna-
data to existing HTML or XML pages. It presents SOAP
tives, a FIPA 2000 Agent Platform description [14] is used as
serialisati on as an alternative. In contrast to [16], the sug-
a common example here, where the serialised instances are
1
taken from the Paris Agentcities no de ApDescription . Al-
though the Paris no de Agent Platform Description consists , the corresp onding RDF serialisa-
Permission to make digital or hard copies of all or part of this work for of four small ob jects only
erb ose. personal or classroom use is granted without fee provided that copies are tion gure 1 b ecomes rather v
not made or distributed for profit or commercial advantage and that copies
rdf:Description elements are
bear this notice and the full citation on the first page. To copy otherwise, to In the RDF example, the
y their abbreviated form for improved republish, to post on servers or to redistribute to lists, requires prior specific already replaced b
permission by the authors.
1
city.html, the ttp://www.agentcities.org/Cities/ pari s
Semantic Web Workshop 2001 Hongkong, China see h
y \Camel" syntax for compatibility Copyright by the authors. dashes are replaced b
Figure 1: RDF Syntax Example
readability. The example enco ding is not the only RDF en-
co ding option, though. RDF allows several syntax variants:
Resource description and typ e abbreviation: An
rdf:Description elementmay b e replaced byan
element named like the typ e of the resource describ ed,
...
also obsoleting a corresp onding rdf:type element.
In the example, the abbreviated form was already
used. All ob ject descriptions in the example could
b e replaced by the corresp onding standard form. For
example,
is equivalentto
...
is equivalentto
...
...
The various RDF syntax options lead to two main prob-
lems: XSLT and XML Schema compatibility problems and
Obviously, the second variant adds ve extra elements
problems with human readability. to the example co de.
3.1 XSLT Compatibility
The Extensible Stylesheet Language Transformations
Using attributes instead of elements: RDF elements
XSLT were designed with the main goal of separating the
may b e replaced by attributes if they o ccur only once
content and layout of Web pages. The basic idea is to de-
in their parent element, and contain only literal text
sign the original page using an XML language. The XML
without further substructures. For example, some of
content is then converted to a \regular" X HTML page by
the ApDescription sub-elements could b e replaced by
an XSLT template.
attributes:
The various RDF enco ding options describ ed ab ove make
development of XSLT templates for RDF dicult: In or-
der to b e fully applicabl e to RDF, XSLT templates would
need to de ne a mapping covering all p ossible syntax alter-
natives. It would certainly b e p ossible to design relatively
simple XSLT templates for one concrete serialised form of
RDF. But then the XSLT transformation would b ecome ei-
...
ther very fragile, or another pro cessing step converting any
RDF le to the form exp ected by the template would b e
necessary.
alentto
is equiv 3.2 Human Readability
Another problem with RDF is human-readabili ty. While
one of the original ideas of XML is to provide some kind of
compromise b etween machine and human-readabili ty, RDF name="paris.agentcities.org" is actually dicult to read for humans. Again, the main dynamic="true" mobility="true"> ... reason are the meta language ro ots of RDF. With the various
syntax options, it is even quite dicult to just see if two
RDF do cuments are semantically equivalent. In order to
read RDF do cuments, a human must b e familiar with all
syntax variants of RDF. When RDF is used to annotate an
existing HTML page, the situation b ecomes even worse since Nesting instead of linking Instead of referring to an ob-
it is often dicult to di erentiate b etween RDF annotation ject using the rdf:resource attribute, the corresp ond-
and actual content. In addition, the verb osity of RDF makes ing ob ject can b e emb edded into the predicate element.
it dicult to read when compared to other XML languages In the original example, all ob jects are emb edded for
or SOAP. b etter readability.
tuitive mapping.
4. RDF DATA MODEL ISSUES The main problem is that there is no in
All mappings have their own advantages and disadvantages,
While it seems relatively simple to x the problems con-
without one b eing clearly preferable to the others. More-
cerning the RDF syntax, this is far more dicult for the
over, except from the facets solution, which has the dis-
RDF data mo del.
advantage of extending RDFS, it is not p ossible to apply
The RDF data mo del is very simple. It is basically a
the inverse mapping to any RDFS schema without precon-
lab elled graph consisting of subject predicate object
ditions. The inverse mapping is only p ossible if the RDFS
triples. With the RDF Schema language RDFS [5] , the
is already of the right "form". It is not p ossible to gen-
data mo del b ecomes signi cantly more structured. RDFS
erate compatible RDF among di erent mappings by using
intro duces a typ e system that can b e used to express prop-
the output from one mapping as input for another inverse
erty constraints. Figure 2 shows the RDFS diagram corre-
mapping. So even if all mappings are using RDFS as their
sp onding to the RDF example. An corresp onding Uni ed
target format, that do es not help for interop erabil i ty at all.
Model ling Language UML [17] diagram of the ontology is
Furthermore, this problem do es not only a ect connecting
shown in gure 3.
existing systems to the Semantic Web, but also ontology
To some extent, RDFS is similar to ob ject oriented struc-
design using UML [9]. When using UML in the ontology
tures, except that prop erties must have globally unique
design pro cess, it b ecomes necessary to take sp ecial care of
names. The RDFS sp eci cation claims that the prop erty
prop erty names again.
centric approach makes it "very easy for anyone to sayany-
Concatenating a prop erty name with the domain name or
thing they want ab out existing resources, which is one of
a namespaces may also create problems for derived classes
the architectural principles of the Web". However, deviating
inheriting that prop erty. All derived classes are a valid do-
from \standard" ob ject orientation also raises some interop-
main for the prop erty, to o, but one would need to remember
erability issues with existing system or mo delling to ols.
the domain where the prop ertywas de ned for constructing
t name and thus b eing able to access the prop erty.
4.1 Compatibility to Object Oriented Systems the righ
Another signi cant di erence b etween the RDFS data
Unfortunately, treating prop erties as rst class memb ers
mo del and standard ob ject oriented systems is that a
of the data mo del makes it imp ossible to map existing ob-
resource can have more than one typ e. For example,
ject hierarchies or database systems to RDFS automatically,
the Prot eg e system is not able to handle this without
without additional handling of prop erty names to ensure
workaround. Prot eg ewas designed to allow only one class
global uniqueness. This is not just a problem with ob ject-
for each instance b ecause of user interface consideration s.
oriented systems or relational databases, also knowledge sys-
Prot eg e solves the problem byinternally creating arti cial
tems likeOntobroker [11] or Prot eg e [12] are seriously af-
concepts that are merged from the di erenttyp es of a re-
fected. When prop erties have a global domain and range
source.
de nition, it is not p ossible to re ne the de nition in a sub-
Please note that two di erent descriptions of one ob ject
class. It is also not p ossible for di erent classes to use the
can exist without requiring that an ob ject is allowed to have
same prop erty name with di erentvalue and domain restric-
several typ es. The describ ed ob ject and the descriptions just
tions [19].
need to b e separate ob jects.
In order to work around this problem, di erent mappings
ving their own advantages and disadvan-
already exist, all ha 4.2 Statements about Statements
tages, and it is quite simple to invent new ones. Possibili ties
The RDF data mo del is a set of subject predicate
are:
object statements, where the statements themselves do
not have an address. In order to b e able to make statements
Facets: Facets were added to RDF by Stefan Decker to sim-
ab out statements, it is necessary to mo del the original state-
plify RDF compatibili ty of the Prot eg e system [18].
ment as a resource having a sub ject, a predicate, an ob ject,
The idea b ehind facets is to allowmultiple ranges and
and a typ e.
re nements for prop erties. The mapping problem for
ed byintro ducing con-
other OO systems could b e solv 5. SOAP
icting prop erties at a common base class and intro-
A p otential alternative to RDF may b e contained in
ducing the actual restrictions later where needed.
the Simple Object Access Protocol SOAP [3] sp eci cation.
Name Concatenation: Stephen Crane eld designed an SOAP is a sp eci cation covering remote pro cedure calls over
HTTP. It contains an ob ject serialisatio n format that can
XSLT template mapping the prop erty names to glob-
ally unique names by just concatenating them with the b e compared to the Resource Description Format RDF to
some extent, even if RDF is not just an ob ject serialisati on
class names [8]. Applied to the UML diagram repre-
senting the course sample schema shown in Figure 3, format. Although RDF was already existing when SOAP
the generated RDF Schema would b e identical to Fig- was b eing sp eci ed, RDF was not chosen as the default se-
rialisation format for SOAP. Instead, SOAP intro duces a
ure 2, except that all prop erty names were concate-
nated the corresp onding domain name. For example, completely new format de ned from scratch.
SOAP is supp orted by computer industry leaders like Mi-
name would b e renamed to ApDescription.name.
crosoft, IBM and SUN. The simplicityofSOAP together
Other options: It is quite simple to invent other mecha- with the supp ort from the industry suggests that many
nisms to ensure globally unique prop erty names. For SOAP-based services will b e available in the near future.
example, a dedicated XML namespace could b e as- While industry supp ort is usually not really relevant for re-
signed to each ob ject, preserving the original name search, research in Arti cial Intelligence may take signi cant
but requiring extensive usage of XML namespaces. advantage from the amount of structured data provided by name
range rdf:type ApDescription domain domain dynamic rdf:type rdfs:Property
rdf:type
rdfs:Class rdf:type rdf:type
rdf:type transportdescription range Literal rdf:type ApTransportDescription range
domain availableMtps rdfs:subclassOf
rdfs:ressource
rdfs:subclassOf mtpName range rdfs:Bag domain MtpDescription domain profile
addresses
Figure 2: RDF Schema of the FIPA AP description
ApDescription ApTransportDescription MtpDescription +name:String +profile:String +dynamic:boolean +mtpName:String +mobility:String +addresses:String[] 1 1..*
transportProfile availableMtps
Figure 3: UML Diagram of the FIPA Agent Platform Description
a Semantic Web that is widely accepted and used. SOAP expressions in ob ject oriented programming or query lan-
Implementations are available for a wide range of program- guages. If the typ e of a prop erty is not xed, it can b e re-
2
ming languages C++, Java, Perl, Python . In contrast to solved by adding a typ e attribute e.g. HTML, SOAP is de ned for direct communication b etween xsi:type="ApTransportDescription"> . Moving the typ e machines over the Internet, so it may a ect the Semantic information into an attribute maintains the advantage of the Web in manyways or even b ecome a signi cant part of it. reduced nesting level when compared to RDF. SOAP is suitable for all kinds of automated Internet services Similar to RDF, SOAP allows alternative syntax forms for likeweather forecasts, trac services, or logistics co ordina- emb edded and referenced ob jects, but in contrast to RDF tion. Although SOAP supp orts alternative content formats, the sp eci cation contains clear rules when an ob ject is em- it is likely that most of the content will actually b e enco ded b edded and when it is referenced: Ob jects maybeemb edded using SOAP serialisati on. Thus, some questions arise: How if there exists only one referenced to them, otherwise they can SOAP b e integrated into the Semantic Web? Can the are linked. And in contrast to RDF, SOAP serialisati on Semantic Web pro t from SOAP services? do es not allow additional abbreviated or alternative XML In his WWW9 presentation, Henrik Frystyk Nielsen [16] syntaxes. Actually, there is no need for an abbreviated syn- demonstrated how RDF can b e enco ded utilisin g the SOAP tax since SOAP serialisati on is compact enough in the rst serialisati on syntax. While he states in his presentation that place. SOAP is not meant to replace RDF, this is clearly one of the The complete sp eci cation of SOAP serialisatio n syntax p ossible future scenarios in the areas where \Semantic Web" is given in [3]. means exchange of information that is machine readable in the rst place. 5.3 SOAP Data Model AP is based on a simple ob ject oriented data mo del. 5.1 SOAP and CORBA SO The SOAP Data Mo del consists of structured ob jects having Although SOAP was originall y designed as a remote prop erties and a typ e. Thus, the basic building blo cks are metho d invo cation proto col running over the Internet, more complex than plain RDF. However, when compared SOAP is not just another Common Object Request Broker to RDFS, there is no signi cant di erence. Larger basic Architecture CORBA . SOAP di ers from CORBA in sig- building blo cks mayhave advantages e.g. when tracking the ni cant p oints: source of statements: The source information would b e at- tached to just one ob ject instead of needing rei cation for a Human Readability: In contrast to the CORBA Inter- lot of RDF statements. Also, when constructing URLs from net Inter ORB Proto col I IOP , SOAP is not a bi- OIDs, it b ecomes very simple to make statements ab out nary format but an XML-based format that is human- statements, again avoiding explicit rei cation that would b e readable. Even if SOAP is mainly intended to b e read required in RDF. by machines, human readabilityisvery helpful for de- In contrast to RDF, SOAP do es not come along with its bugging purp oses and quick implementation. own schema language. Instead, XML Schema is used for validation of the syntactical correctness of SOAP serialised Simple Installation: While CORBA requires huge soft- ob jects. While XML Schema do es not seem the appropriate ware packages and do es not provide a commonly ac- level of ontology mo delling, SOAP serialisation ts well into cepted b o otstrapping mechanism, SOAP is based on UML mo delling without the prop erty naming problems of HTTP and can b e implemented with little e ort on RDF. And when comparing the RDFS and UML diagrams top of existing libraries for XML and HTTP. gure 3 and gure 2 , UML seems signi cantly more ap- propriate for mo delling ontologies. Even if SOAP still lacks a reasonable security mo del, it has the p otential to b ecome the connecting p ointbetween va, Perl and Microsoft's .NET architecture by just o ering Ja 6. IS SOAP SUITABLE FOR THE SEMAN- a suitable feature set, while still b eing simple enough to b e TIC WEB? implemented by a broad range of programmers. As shown in the preceding sections, SOAP has advantages ver RDF in several areas. But do es that mean that SOAP 5.2 SOAP Syntax o is sucient to build a \Semantic Web"? The Semantic Web Probably the main reason for SOAP b ecoming quite p op- is meant to b e more than just turning some existing ob ject- ular in the very short time it is available now is its simplicity. oriented systems into SOAP services. How can a collection The serialised format of the FIPA example enco ded in SOAP of SOAP services evolveinto a Semantic Web? Are there any is shown in Figure 4. The format is much more similar to RDF core features missing in SOAP? Can the advantages of an XML sp ecial purp ose format designed \by hand" than SOAP and RDF b e combined to accelerate or simplify the the RDF serialisation . pro cess of building a Semantic Web? The main di erence visible on rst glance is the re- el of XML elements. In RDF, b oth ob- duced nesting lev 6.1 Using SOAP Syntax for the RDF Data ve their own tags. In SOAP, the jects and prop erties ha Model nested tags starting a new ob ject are always merged with Henrik Frystyk Nielsen [16] suggests to apply SOAP seri- the prop erty tags if p ossible. This also has the advantage alisation to the RDF data mo del to simplify integration of that navigating through a SOAP serialised do cument us- the SOAP RMI proto col with RDF data. Since this would ing path expressions b ecomes very similar to usual path mean yet another alternative syntax, the RDF syntax sit- 2 uation would not b e simpli ed, except if the new syntax http://www.sup erop endirectory.com/d irecto ry/4/ b ecame the only one. But limiting RDF syntax variants standards/23/impl ementa tion s Figure 4: SOAP Syntax Example ould generate problems when using RDF for its in general w 6.3 Schema Language original purp ose of annotating existing do cuments. Also, the The SOAP sp eci cation do es not contain anyschema lan- prop osed syntax would not help for a seamless integration guage, but refers to XML Schema for syntax validation . of other SOAP-based services since the prop erty mapping However, a syntax sp eci cation language like XML Schema problem would p ersist. is not really suitable for mo delling ontological elements like classes, attributes and asso ciations. Actually, the SOAP sp eci cation just describ es how to get an XML Schema from ersa. 6.2 Saying Anything about Anything the data structure and not vice v But even if SOAP do es not come along with its own In [2], Tim Berners-Lee justi es the usage of the prop erty- schema language, the SOAP data mo del ts quite well into centric data mo del instead of an \usual" ob ject-oriented UML. Thus, UML to ols can b e used for mo delling, without data mo del by claiming that ob ject-oriented systems gen- the limitations shown for the RDF case. erally assume that information ab out an ob ject is stored Furthermore, even if SOAP describ es instance serialisa- inside that ob ject. So, in order to b e able to sayanything tion only, the UML meta mo del [17] can still b e utilised ab out anything, it b ecomes necessary to store the prop erties to serialise UML mo dels using SOAP serialisati on syntax. apart from the ob ject. Some UML constructs would require the de nition of a con- While for ob ject oriented systems it is true that prop erty crete mapping, but there is no general incompatibil ityin information is stored with the ob jects, this do es not mean the data mo del. Distinction b etween di erenttyp es of as- that ob jects cannot hold information ab out other ob jects. so ciations in UML could also b e utilised to de ne the cases So there is no real requirement that e.g. the PICS rating where emb edded ob jects are allowed in SOAP serialisati on of an HTML page is a prop erty of that page. It could also more clearly. b e a separate ob ject holding a p ointer to the original page. A more complex example could b e a car b eing the primary y. ob ject and its description stored at an insurance compan 6.4 Integration of existing Services and Sys- tems Even if a \standard" ob ject-oriented data mo del is suit- able for the Semantic Web, there is still a problem with In his XML2000 keynote, Tim Berners-Lee suggested to SOAP. The SOAP sp eci cation do es not sp ecify how to as- use "screen-scrap er"-like XSLT templates to convert XML sign URLs to ob jects. There is also no general mechanism to into RDF for the starting century of the a Semantic Web say \something" ab out a given URL. However, it seems rel- [1], like shown in gure 5. However, the SOAP serialisati on atively simple to assign URLs to ob jects built from the ser- syntax is simple enough to b e widely accepted as a general vice address and a lo cal unique numb er OID . If an ob ject XML mo delling convention. So it may b e p ossible to elim- is intended to describ e a resource, it could have an \ab out" inate the need for an additional \screen scraping" template prop erty like in the SOAP-enco ded RDF syntax prop osed in many cases. Also, the compatibili ty with XSLT allows by Henrik Frystyk Nielsen [16]. building HTML or WML transformation templates, just like for XML languages designed \by hand". Moreover, since SOAP ts nicely into existing ob ject ori- ented and relational database systems, it may simplify the schema generation pro cess. Instead of needing to design an XML DTD or XML Schema, it would b e sucient to agree on an UML diagram, allowing a much more appropriate level of abstraction. AP advantage is that SOAP quite nicely in- Server (XML) Another SO tegrates with a lot of existing standards Table 1 . This was already discussed for XSLT and UML, but we also have awell designed query language for ob ject oriented systems. The Ob ject Query Language OQL [7], designed by the Ob- ject Data Management Group ODMG ts p erfectly with AP and preserves a high degree of SQL compatibili ty. HTML Transformation SO RDF "Screen Scraper" (XSLT) (XSLT) 7. WHAT IS MISSING For a real \Semantic Web", the upp er logical levels are Browser (HTML) Software Agent missing from SOAP. But this holds for RDF as well, and lo oking at existing inference systems, it do es not seem more dicult to build them for SOAP than for RDF [13]. Also, mechanisms for schema translations may b ecome Figure 5: RDF screen scraping necessary. For example, if a legacy system with a direct SOAP mapping needs to b e adapted to a SOAP based stan- dard, or if SOAP based standards for di erent areas need to interop erate. However, this will probably b e more sim- ple than general XML-XML translations, where XML-XML translations are p ossible to day using XSLT. Again, the same would b e necessary for RDF. 8. CONCLUSION Obviously,wehavetwo formats and data structures that are similar to some extent, and b oth are relevant for the \Semantic Web", esp ecially when the term means something di erent than annotation of existing pages with additional meta data. The main problem is that b oth approaches are dicult to translate into each other. RDF SOAP In contrast to SOAP, RDF is suitable for \in place" anno- tation of existing web pages. For b eing able to say \anything Serialisati on RDF SOAP ab out anything", RDF uses URLs as global unique identi- ers. HTML/WAP generation ? XSLT Although SOAP is not suitable for \in place" annotation and would require an extension assigning URLs to ob jects Query Language ? OQL in order to b ecome really suitable for the Semantic Web, it has several advantages in other areas. SOAP ts quite well Syntax Validation ? XML Schema into other standards like UML, XSLT and OQL. It provides a clear and simple syntax. The SOAP Serialisatio n syntax Schema Serialisati on RDFS UML Meta-mo del nearly reaches the quality of a \hand-made" one. Thus, SOAP serialisation is suitable as content enco ding conven- Schema Mo delling ? UML tion in the rst place. So, in contrast to RDF, an extra conversion step can b e avoided completely. The logical level is not yet covered for b oth approaches, Table 1: Integration with existing standards RDF and SOAP. For the future, it seems to make sense to work on b oth approaches without do oming the other. Even if lo oking at SOAP may split the Semantic Web community to some ex- tend, comp etition may also set free a lot of development energy.Perhaps the logical layer to b e built on top of RDF and SOAP may allow for an integration of b oth approaches at some future p oint of time. rystyk Nielsen. Soap, RDF and the Semantic 9. REFERENCES [16] Henrik F Web. In WWW9, 2000. [1] Tim Barners-Lee. RDF and the Semantic Web. In [17] Ob ject Management Group. OMG Uni edModeling XML 2000. GCA, 2000. Language Speci cation, June 1999. Version 1.3. [2] Tim Berners-Lee. What the smantic web can [18] Stanford University. Using Prot eg e-2000 to Edit RDF, represent, Septemb er 1998. June 2000. http://www.w3.org/DesignIssues/RDFnot.html. http://www.smi.stanford.edu/pro jects/protege/ protege - [3] Don Box, David Ehnebuske, Gopal Kakivaya, Andrew rdf/protege-rdf-20000629.html. Layman, Noah Mendelsohn, Henrik Frystyk Nielsen, [19] Frank van Harmelen and Dieter Fensel. Practical Satish Thatte, and Dave Winer. Simple Ob ject Access knowledge representation for the web. In IJCAI'99 Proto col soap 1.1. Note, World Wide Web Workshop on Intel ligent Information Integration, Consortium, 2000. 1999. http://www.w3.org/TR/2000/NOTE-SOAP- 20000508. [4] Dan Brickley. RDF interest group - issue tracking. Technical rep ort, World Wide Web Consortium, 2000. http://www.w3.org/2000/03/rdf-tracking/. [5] Dan Brickley and R. V. Guha. Ressource Description Framework RDF Schema sp eci cation 1.0. Technical rep ort, World Wide Web Consortium, 2000. http://www.w3.org/TR/CR-rdf-schema-20000327. [6] Dan Brickley and Ralph R. Swick. PICS rating vo cabularies in XML/RDF. Technical rep ort, World Wide Web Consortium, 2000. http://www.w3.org/TR/2000/NOTE-rdf-pics- 20000327. [7] R. G. G. Cattell, editor. The Object Database Standard: ODMG 2.0. Morgan Kaufmann, 1997. [8] S. Crane eld. Networked knowledge representation and exchange using UML and RDF. Journal of Digital Information, 1 8 , 2001. http://jo di.ecs.soton.ac.uk/. [9] S. Crane eld and M. Purvis. Uml as an ontology mo delling language. In Proceedings of the Workshop on Intel ligent Information Integration, 16th International Joint ConferenceonArti cial Intel ligence IJCAI-99, 1999. [10] Stefan Decker. Prop osed up dates of RDF, 1999. http://www-db.stanford.edu/stefan/up dates.html. [11] Stefan Decker, Michael Erdmann, Dieter Fensel, and Rudi Studer. Ontobroker: Ontology based access to distributed and semi-structured information. In R. Meersman and other, editors, Semantic Issues in Multimedia Systems, Kluwer Academic Publisher, Boston, 1999. Kluwer Academic Publisher, Boston, 1999. [12] H. Eriksson, R. W. Fergerson, Y. Shahar, and M. A. Musen. Automatic generation of ontology editors. In Twelfth Ban Know ledge Acquisition for Know ledge-based systems Workshop, Ban , Alb erta, Canada, 1999. [13] A. S. Evans. Reasoning with UML class diagrams. In Proceedings of the Workshop on Industrial Strength Formal Methods WIFT'98 . IEEE Press, 1998. http://www.cs.york.ac.uk/puml/pap ers/evan swift.p df. [14] Foundation For IntelligentPhysical Agents FIPA . FIPAAgent Management Speci cation, 2000. http://www. pa.org/sp ecs/ pa00023/XC00023 F.p df. [15] Ora Lassila and Ralph R. Swick. Ressource Description Framework RDF mo del and syntax sp eci cation. Technical rep ort, World Wide Web Consortium, 1999. http://www.w3.org/TR/1999/REC-RDF-SYNTAX- 19990222.