NOTE: This paper and the other pages on this web site are preserved here mainly for historical reasons. They have been prepared in the years 2000 and 2001, when the specifications of RDF and RDFS were still somewhat tentative. Not all of the links work anymore. However, this document may still provide you with some insight into the semantics of RDF -- though beware, the official model theory is where you should look for definitive answers to your questions (though, admittedly, the answers to your questions may not be found there too easily... ;) [Wolfram Conen, April 2008]
An eXtensible Resource Description Framework (XRDF)
(see also: [Online RDF-to-XRDF converter (not online anymore)],
[RDF Schema Explorer (offline)], [A Logical Interpretation of RDF ])
RDF M&S revisited:
From Reification to Nesting,
from Containers to Lists,
from Dialect to pure XML
[PDF]
Proceedings
of the Semantic Web Working Symposium
(SWWS), Juli-August, San Jose, CA,2001
This paper is also selected for inclusion in the book "The emerging
semantic web"
(a compilation of selected papers of the SWWS which
will be published this spring by IOS press).
[PDF]
of book version (differences result from removing errors and a little
bit "beautifying" in appearance)
ABSTRACT
Abstract. The basic result presented is the following: with two (hopefully reasonable) assumptions about the intentions behind the RDF model, it can be shown that the RDF
model and a model allowing for nested triple and lists of resources and triples, can be mapped to one another (in both directions). This allows to establish a close link between
the RDF model and extended models recently suggested (SlimRDF, XRDF). Further, the approach may help to clarify some problems related to inter-preting the roles of
reification and containers in the RDF model.
Authors
Wolfram Conen, conen [a] gmxi [.] de
Reinhold Klapsing, formerly University of Essen, Germany
Eckhart Köppen, eck [a] 40hzi [.] org formerly University of Essen, Germany
An eXtensible Resource Description Framework (XRDF)
ABSTRACT
This paper presents a nested triple model for expressing relations
found in the Web. The model allows grouping of atoms and statements on
subject and object position. It preserves the structural context in
which resource are used. Additionally, we propose a (pure) XML
serialization syntax and a graphical representation which equivalently
express the formal concepts. On top of the basic structural layer,
semantic definitions and interpretations can be layered. One such
layer is presented. Finally, the relation of this approach to RDF is
discussed and it is argued, that most of the perceived deficiencies of
RDF are non-issues in the context of XRDF.
History
Authors
Wolfram Conen, conen [a] gmxi [.] de
Reinhold Klapsing, formerly University of Essen, Germany
Eckhart Köppen, eck [a] 40hzi [.] org, formerly University of Essen, Germany
Below, you find a brief review of the key features and some general
remarks on our intentions.
Some key features are:
- A simple structural "model":
In the following definition, the (infinite)
alphabet A* will be used. A* will denote all
possible instances of PCDATA in well-formed XML.
We define the structure R recursively as an expression over A* as
R ::= r | R,R | [[R],r,[R]]
The terminals r denote elements of A*. (you may call the possible
structures "resources", but we tried to keep it free from
interpretation even on this basic level)
- A straightforward XML sntax correspong to the structural model,
<!ELEMENT statement (subject, predicate, object)>
<!ELEMENT list (statement | atom)+>
<!ELEMENT atom (#PCDATA)>
<!ELEMENT subject (atom|statement|list)>
<!ELEMENT predicate (atom)>
<!ELEMENT object (atom|statement|list)>
- A graphical model directly corresponding to the structural model,
allowing for grouping/sequencing.
- Some basic transformations are given, allowing to (de)reference
representations, to "dissolve" n:m,1:m,n:1 relations etc. These
basic tranformation can be used to embed the XRDF structures into a
host formalism (such as FOL) (or, in other words: to transform XRDF
expressions into "menaingful" expressions in other formalisms.
Some general remarks:
We tried to keep the structural model, the synatactical and graphical
representation and the basic transformations as free from
interpretation as possible. Some will miss terms as "assertions" or
"meaning/interpretation". This paper is a "part I" that tries to
offer a simple (yet powerful) recursive "data model" with "positions"
(based on triples again ;), a straightforward syntax that allows to
"build" deeply nested expressions with complex (syntactical)
structure (neat for "context"), and some basic (structural)
transformations tied to "predicates" (that are the "things" in the
middle of a triple). There is no semantics yet - instead we tried to
provide the ingredients that allows to plug the XRDF stuff into
suitable formalisms (by offering the tools that are needed to
transform structured expression into a different "language", which
may/should then be used to give meaning/interpretation to the XRDF
constructs. We do not think that fixing interpretations on this level
of langugae design is necessary or suitable - we feel that different
interpretations in different formalisms should be possible easily. We
hope that the discussion will show that there is much more to say.
Please, allow one more word: we did not intend to "replace" RDF -- we
have a simple RDF-to-XRDF converter online [not online anymore, Remark added in April 2008 by Wolfram] and a "XRDF flatener" is
available in alpha version that allows, with a suitable set of
additional semantic rules, to convert XRDF to RDF (using reification,
position information, and dereferencing) -- instead, we thought that
it might be fruitful to discuss a somewhat "clear-cut" approach to
show which problems of RDF need to be tackled and how possible
solutions may look like.
Thank you in advance,
Wolfram, Reinhold, Eckhart
PS1: Any comments/questions/remarks are welcome. If you think that
the question/comment is not (yet) of public interests, you may want
to send it to [outdated] only, otherwise, you
may also want to CC it to the RDF-IG [outdated]. We will collect all discussion
on a Web page that will be accesible via
http://nestroy.wi-inf.uni-essen.de/rdf/xrdf.
PS2: We wrote the initial version Oktober 2000. We decided to submit
it to the WWW10 conference -- mainly because, due to some unfortunate
personal circumstances, there would have been no possibility to
follow a possible discussion on the RDF-IG -- however, the paper was
(and still is) initially intended to be a contribution to the
RDF-IG. In the meantime, the time constraints have relaxed (so we are
ready to start the discussion now! ;) and we have received the
comments from the 3 reviewers. Two have been positive (7 and 6)
(including encouraging comments) and one was negative (3) (without
further comments) -- which is not enough to allow travelling to
Hongkong but instead gives more time to work on discussing and
improving the stuff.
XRDF-Team