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RDF/Topic Maps Interoperability Survey

Introduction to the Draft Survey

SWBPD WG F2F

Boston

March 4th 2005

 

These slides available at http://www.ontopia.net/work/survey-pres.html

 

Steve Pepper

Chief Strategy Officer, Ontopia

Coordinator, RDFTM TF

<pepper@ontopia.net>

Survey: Purpose and target audience

  1. Purpose: To prepare the ground for the Guidelines
    • Demonstrate that the Guidelines are based on a solid assessment of previous work
    • Clarify the issues for the Task Force members
    • Develop an understanding of requirements and possible trade-offs
    • Justify the adoption of the semantic mapping approach
  2. Target Audience: Specially interested parties only
    • Anyone with a particularly deep interest in the problem and consequently greater than passing familiarity with both paradigms
    • In particular, the pioneers of RDF/TM interoperability
    • Estimated size of audience for Survey < 50
      • NB: Estimated size of audience for Guidelines: > 50,000

Document structure

  1. Introduction
  2. Criteria for evaluating the proposals
  3. Existing translation proposals
    • Moore
    • Stanford
    • Ogievetsky
    • Garshol
    • Unibo
  4. Analysis
  5. Conclusion

1 Introduction

2 Criteria for evaluating the proposals

2.1 Translation features

Completeness
The criterion completeness is used to evaluate the extent to which each proposal is able to handle every semantic construct that can be expressed in the source model and provide a means to represent it without loss of information in the target model. A complete translation will by definition be reversible.
Fidelity
The criterion fidelity expresses the degree to which the results of a translation are faithful to the underlying conceptual model of the target paradigm. This quality can be thought of as naturalness, that is, as corresponding to the way in which someone familiar with the target paradigm would naturally express the information content in that paradigm. Naturalness normally also confers improved readability on the result.

2.2 Major issues

Topic Maps issuesRDF issues
IdentityContainers
ScopeCollections
N-ary associationsLanguage tags
Association rolesXML literals
VariantsTyped literals
Reification 

2.3 Test Cases

3 Existing translation proposals (1)

(Presented in chronological order)

3 Existing translation proposals (2)

4 Analysis

4.1 Object mappings and semantic mappings

Object mappings
Object mappings use the low-level building blocks of one language to describe the object model of the other.
For example, assuming for now that the structure of a simple binary associations data model is a quintuple, consisting of one (a)ssociation, two (r)oles, and two role (p)layers (p-r-a-r-p), that association would be represented as four statements that relate five resources.
Semantic mappings
Semantic mappings start from high-level concepts that carry the semantics of each model and attempt to find equivalences between them.
For example, a binary association in Topic Maps would be seen to represent the same kind of "thing" that many RDF statements represent (i.e., a relationship between two entities) and would therefore be represented using a single RDF statement.

4.2 The importance of being faithful

Fidelity is important because the result of low-fi translation is structurally different from data created in the target model.

This leads to reduced interoperability, in the following ways:

  1. The result will not merge cleanly with data originating in the target model,
  2. The result will not conform to vocabularies created in the target model, and
  3. Queries written against the target model will not work with translated data.

Hi-fi and low-fi queries

Query with hi-fi semantic mapping
SELECT ?c
WHERE (?m, <foaf:name>, "Lars ..."),
      (?c, <dc:creator>, ?m)
Query with low-fi object mapping
SELECT ?c
WHERE  (?m,  <tm:basename>, ?n),
       (?n,  <tm:value>,    "Lars ..."),
       (?r1, <tm:player>,   ?m),
       (?r1, <rdf:type>,    <:creator>),
       (?a,  <tm:role>,     ?r1),
       (?a,  <rdf:type>,    <:created-by>),
       (?a,  <tm:role>,     ?r2),
       (?r2, <rdf:type>,    <:creation>),
       (?r2, <tm:player>,   ?c)

4.3 Semantic mapping issues

5 Conclusion

 

NB Conclusion deliberately left sketchy until WG has provided feedback on first draft

Reviews

Questions?

Questions! (1 of 2)

  1. Should the Survey be a tutorial or should it assume some familiarity with both RDF and Topic Maps on the part of the reader?
  2. Should OWL be covered in full, or only as it impacts data interoperability?
  3. Is it OK to mention commercial implementations provided this is done in context and with a purpose?
  4. Natasha questioned whether the survey is objective. Does it need to be? Isn't fairness enough?
  5. Is anyone not convinced by the argument for a semantic mapping?

Questions! (2 of 2)

  1. Should the two test cases have identical information content?
  2. Should the test case results be moved to separate documents?
  3. Are our "issues" really "requirements"? If not, do we need a set of formal requirements in this document, or should they be in a separate document?
  4. Should we use the term "naturalness" rather than "fidelity"?
  5. Is it acceptable to require mapping information?

RE: On the integration of Topic Maps and RDF

http://lists.w3.org/Archives/Public/www-rdf-interest/2001Aug/0155.html
From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 21 Aug 2001 11:28:05 -0400
To: em@w3.org
Cc: lacher@db.stanford.edu, www-rdf-interest@w3.org
Message-Id: <20010821112805Z.pfps@research.bell-labs.com>

One important aspect of such mappings, for me, is whether information expressed naturally in the source formalism (Topic Maps) and then translated into the target formalism (RDF) can be naturally integrated with information expressed naturally in the target formalism. If this is not the case, then I claim that there is something wrong with the translation.

I feel that the translation expressed in the paper does not satisfy this criterion. Consider the example topic map in the paper, which, among other things, expresses the fact that petroleum is a natural resource of Denmark. It seems to me that the natural way of expressing this in RDF is to have a resource representing Denmark (D), a resource representing petroleum (P), and a predicate representing the natural resource relationship (NR). Then the fact that Denmark has petroleum as a natural resource is represented as the statement . The mapping in the paper uses much more machinery than this natural representation, including two reified statements.

Suppose some facts about natural resources come from topic maps, and are represented in this translation to RDF, and other facts about natural resources come from a natural RDF representation. How can one query the RDF to find the union of the facts? Even if it is possible to write a such a query is it at all possible to write such a query without knowing that some of the natural resource facts come from topic maps?

Peter F. Patel-Schneider

Bell Labs Research

RE: On the integration of Topic Maps and RDF

http://lists.w3.org/Archives/Public/www-rdf-interest/2001Aug/0158.html
From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 21 Aug 2001 14:47:04 -0400
To: lacher@db.stanford.edu
Cc: em@w3.org, www-rdf-interest@w3.org, gdm@empolis.co.uk
Message-Id: <20010821144704U.pfps@research.bell-labs.com>

I think that we will have to "agree to disagree" on whether mappings between Topic Maps and RDF should preserve meaning.

I strongly, no, passionately, believe that such mappings have to be model-mappins that preserve meaning, at least if one is to hold the view that RDF is a representation formalism. If RDF is a representation formalism, then positive ground binary relations have to be represented as RDF triples. Otherwise, RDF is just some syntactic encoding, and the entire meaning is conveyed in some outside-of-RDF (and, probably, outside of the web) side agreement.

Any approach that requires an outside-of-RDF approach to ascribe meaning to the resulting RDF has, in my opinion, lost everything. Yes, an approach that stays within RDF has the potential of losing some things, but at least the portion that can be naturally represented in RDF is completely captured.

Peter F. Patel-Schneider

Bell Labs Research

RE: On the integration of Topic Maps and RDF

http://lists.w3.org/Archives/Public/www-rdf-interest/2001Aug/0184.html
From: Martin Lacher <lacher@db.stanford.edu>
Date: Thu, 23 Aug 2001 16:27:11 -0700
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: <em@w3.org>, <www-rdf-interest@w3.org>, <gdm@empolis.co.uk>
Message-ID: <NEBBIEAODMJKOIMFPAEBGEHPCLAA.lacher@db.stanford.edu>

Hi Peter,

Thank you for your comments !

...

We are talking about two different things:

1) Your goal is to be able to query different sources without having to know anything about the data model of the sources. That would be a great solution, I would love to see that for RDF and Topic Maps without substantial loss of information.

2) Our goal was to start out with a way to be able to query different sources the data model of which we know. The agreements you mentioned are partly specified in the RDF schema we defined (with the exception of the representation of the hypergraph elements from the Topic Map data model). The schema needs to be elaborated.

Considering our goal, I think our results are valid.

Cheers,

Martin