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


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).

of book version (differences result from removing errors and a little bit "beautifying" in appearance)


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.


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)


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.


Latest version: [Postscript], [PDF]
Version 1.0: [Postscript], [PDF]


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:

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

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.