IEEE International Conference on Semantic Computing (ICSC 2011). A Multidimensional Semantic Space for Data Model Independent Queries over RDF Data André Freitas, João Gabriel Oliveira, Edward Curry Seán O’Riain http://andrefreitas.org/papers/preprint_multidimensional_ieee_icsc_2011.pdf Abstract: The vision of creating a Linked Data Web brings together the challenge of allowing queries across highly heterogeneous and distributed datasets. In order to query Linked Data on the Web today, end-users need to be aware of which datasets potentially contain the data and also which data model describes these datasets. The process of allowing users to expressively query relationships in RDF while abstracting them from the underlying data model represents a fundamental problem for Web-scale Linked Data consumption. This article introduces a multidimensional semantic space model which enables data model independent natural language queries over RDF data. The center of the approach relies on the use of a distributional semantic model to address the level of semantic interpretation demanded to build the data model independent approach. The final multidimensional semantic space proved to be flexible and precise under real-world query conditions achieving mean reciprocal rank = 0.516, avg. precision = 0.482 and avg. recall =0.491.

1. Digital Enterprise Research Institute www.deri.ie
A Multidimensional Semantic Space
for Data Model Independent Queries
over RDF Data
André Freitas, João Gabriel Oliveira, Edward Curry
Seán O’Riain
 Copyright 2009 Digital Enterprise Research Institute. All rights reserved.

2. Outline
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 Problem Space & Motivation
 Description of the Approach
 Evaluation
 Conclusion & Future Work

3. Linked Data
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 Uses the Web infrastructure and standards to
expose and interlink datasets.
 Linked Data vision:
 The Web as a single Dataspace.
 Web of interlinked datasets.

4. Linked Data: Adoption
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5. Queries over Linked Data
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 Linked Data brings a fundamental challenge for data
consumption:
 How to query heterogeneous and distributed datasets?
 At Web scale it is unfeasible for end-users to be aware of the
location and structure of datasets.
 Demand for new query mechanisms for Linked Data (data
model independency).

6. Query/Search Spectrum
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Adapted from Kauffman et al (2009)

7. Fundamental Problem
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From which university did the wife of
Barack Obama graduate?
 Popescu (2003): Semantic tractability problem.

8. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?

9. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
Entity identification

10. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
Entity search

11. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
Approximate
semantic matching

12. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
Approximate
semantic matching

13. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
Approximate
semantic matching

14. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
Structural matching

15. Semantic Matching Problem
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From which university did the wife of Barack Obama graduate?
T- Space

16. Strategy
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 Best-effort query model (ranked results).
 Use of a distributional semantic model.
 Two phase search process combining entity search
with spreading activation search.

17. Digital Enterprise Research Institute www.deri.ie
Proposed Approach

18. Query Approach Rationale
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19. Query Approach Rationale
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20. Query Approach Rationale
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21. Query Approach Rationale
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Final Query- Data Matching:

22. Semantic Relatedness
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 Computation of a measure of “semantic proximity”
between two terms.
 Allows a semantic approximate matching between
query terms and dataset terms.
 Most existing approaches use WordNet-based
solutions for approximate semantic matching.
 Distributional semantic approaches address these
limitations.

23. Distributional Semantics
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 Assumption: the context surrounding a given word
in a text provides important information about its
meaning.
 Meaning is mediated by word distribution in the
corpora.
 Simplified semantic model.
Opera is an art form in which singers and musicians perform a
dramatic work combining text (called a libretto) and musical score.
Opera is part of the Western classical music tradition. Opera
incorporates many of the elements of spoken theatre, such as acting,
scenery, and costumes and sometimes includes dance. The
performance is typically given in an opera house, accompanied by an
orchestra or smaller musical ensemble.

24. Explicit Semantic Analysis (ESA)
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 Based on Wikipedia.
 Interpretation vector using Wikipedia articles titles.

25. Building the T- Space (Steps)
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 Building the distributional semantic model using
ESA.
 Construction of instances spaces (TF/IDF).
 Construction of classes spaces (ESA).
 Construction of relation spaces (ESA).

26. Building the T- Space
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relations
instances properties
classes

27. Building the T- Space
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28. Instances
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29. Building the T- Space
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30. Classes
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Universal
ESA Space

31. Building the T- Space
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32. Relations
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Universal
ESA Space

33. Building the T- Space
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34. Querying the T- Space
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35. Querying the T- Space
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36. Querying the T- Space
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37. Querying the T- Space
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Treo (Irish): Route, path

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Evaluation

40. Quality of Results
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 QALD DBPedia Training Set.
 50 natural language queries.
 DBpedia 3.6.
Full DBPedia QuerySet (50 queries)
Avg. Precision Avg. Recall MRR % of queries
answered
0.482 0.491 0.516 58%
Partial DBPedia QuerySet (38 queries)
Avg. Precision Avg. Recall MRR % of queries
answered
0.634 0. 645 0.679 76%

41. Error Distribution
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42. Conclusion & Future Work
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 The T-Space semantic model shows a promising direction for
providing data model independent queries over RDF data.
 Improvement of semantic tractability.
 The distributional semantic model supports a flexible
matching between query terms and dataset terms in a best-
effort scenario.
 Further improvements are needed:
 QA features (e.g. answer type detection, operators).
 User feedback mechanisms (disambiguation).
 Entity recognition for complex classes.