bestmap:)context.aware)skos)...

BestMap: Context-‐Aware SKOS Vocabulary Mappings in OWL 2

Rinke Hoekstra

Overview

•  Use Case – Access to court proceedings

•  Vocabulary Mapping

•  Requirements

•  BestMap

•  Discussion

24 October 2009 Rinke Hoekstra -‐ OWLED 2009 1

BestPortal

•  BEST Project – “BATNA Establishment using SemanTc Web Technology”

– Best AlternaTve to a NegoTated Agreement

•  Improve access to court proceedings – Netherlands Council of the Judiciary hYp://www.rechtspraak.nl

– 50 thousand verdicts


“Does my case stand a chance in court?”

•  Full text search is not enough –  Laymen –  Lawyers

•  Lawyers have their own language: legalese –  Bridge the gap between common sense and legal knowledge

•  Knowledge-‐based soluTon too expensive – Modelling effort – Quality assurance –  Legal theory: defini&ons


BestPortal: Requirements

•  Translate layman descripTon to legal terms

•  Search using fingerprints of legal terms

•  Context in which layman concepts co-‐occur in a case determines the applicability of a legal concept

•  A mapping is not the definiTon of a concept 24 October 2009 Rinke Hoekstra -‐ OWLED 2009 4

Layman Vocabulary

Layman Case Description

Case

LegalVocabulary

Legal Case Description

Case Law Database

Mapping

Vocabularies

•  Cultural Heritage – Museums, libraries

– Huge repositories of (rich) informaTon – Annotated using many different vocabularies (knowledge organizaTon systems)

•  Concept-‐based informa&on retrieval – Europeana portal (hYp://www.europeana.eu)


Why Vocabulary Mapping

•  Integrated access? Vocabulary mapping! –  Format (XML to RDF)

•  e.g. via XSLT one-‐way transformaTon –  Structure (VCard:Given + VCard:Family to foaf:name)

•  e.g. via SPARQL++, one-‐way transformaTon –  Concepts (foaf:Person to lkif:Person)

•  Simple Knowledge OrganizaTon System (SKOS) –  Liking exisTng KOS’s to the SemanTc Web –  Every skos:Concept is an OWL individual –  Lightweight seman&c relaTons: broader, narrower, and related. –  Lightweight mapping relaTons between skos:ConceptSchemes.


Europeana Datacloud


Mapping in SKOS

skos:mappingRelation

skos:closeMatch(symmetric)

skos:exactMatch(symmetric, transitive)

skos:broadMatchskos:narrowMatch

skos:relatedMatch(symmetric)

skos:narrower skos:broader

skos:semanticRelation

skos:related

inverse disjoint

disjoint


Informa=on retrieval perspec=ve vs. lightweight seman=cs

•  No many-‐to-‐many mappings – Mapping only between pairs of concepts

– Required for re-‐indexing and search across collecTons (Isaac et al. 2007)

•  … fundamental issue – SKOS concepts and relaTons are ‘intensional’ – What does a mapping then mean?

•  Implicit assumpTon of extensionality


Extensional View

•  SKOS relaTons – “Resources annotated by some concept should be retrievable via its broader concept.”

•  SKOS mappings – “Resources annotated by some concept should be retrievable via the concepts it is mapped to.”

•  … only means to assess quality


BestMap: Requirements

•  Extensional perspecTve –  Concepts as annota&ons on resources

•  CompaTbility –  Integrated with SKOS

•  Hierarchic mappings –  Exploit skos:broader and skos:narrower

•  Many-‐to-‐many mappings –  Granularity –  Context determines whether a mapping holds

•  Flexible and Lightweight –  A mapping is not the definiTon of a concept


ConnecTng to SKOS (1)

•  RelaTon between :Resource and skos:Concept

•  Direct and indirect annotaTons


the location of a crime, etc. However, in our case, the school is most relevant asthe owner of an animal (the horse) that caused some damage (the kick). If theperson being kicked is an employee, then it might also be a case of liability forsubordinates.

Lastly, specifying mappings at this level of specificity is not very flexible,and we should therefore exploit the skos:narrower and skos:broader hierarchy toallow for similar cases to be covered by a single mapping. Section 5 introducesa framework, or design pattern if you will, for specifying context-aware map-pings between two (or more) vocabularies, and specifies means to extend thisframework by including more contextual information using OWL 2 role chains.

5 BestMap: Context-Aware Mappings

As has been made clear in the previous sections, mapping relations often rely onintensional semantics, where the applicability of mappings is often existentiallydefined. In our approach, we exploit the power of OWL 2 DL to define restrictionson the members of sets of annotated resources as intensional descriptions. TheBestMap ontology makes explicit the medium – a resource – through whicha mapping can be specified.11 To do this, we introduce the property :aboutand its inverse that allow us to annotate resources with concepts from a SKOSvocabulary:

:about ≡ inv(:describes)

The :about property relates a :Resource (its domain) with some skos:Concept (itsrange). The reason for introducing a new relation is that other options, such aspunning of SKOS concept individuals, or reusing existing vocabulary are limitedin the sense that they cannot be subject to OWL 2 class restrictions.

As we are dealing with SKOS vocabularies, it seems useful to integrateSKOS’s semantic relations with this approach. There are two issues here. First,simply defining a sub property role chain that reuses :about is not allowed inOWL 2 as it introduces a cycle [3]. We therefore need to distinguish betweendirect annotations, and indirect annotations:

:d about � :about

:d describes � :describes

:d describes ≡ inv(:d about)

Secondly, SKOS makes a distinction between quite a variety of semantic rela-tions. We define sub properties of :about and :describes for each of these, takinginto account the direction of the relation. For instance:

:d about o skos:broaderTransitive � :bt about

:d about o skos:narrowerTransitive � :nt about

11 The BestMap ontology is available from http://www.best-project.nl/owl/bestmap.owl.








:d about � :about








•  TransiTve broader/narrower

•  Similar for other SKOS relaTons


ljn:AE3482 lv:horse

lv:animal

:d_about

skos:broaderTransitive

:bt_about

lv:animal

skos:narrowerTransitive:nt_about








:d about � :about









:cm_about

:em_about

:bm_about :rm_about

:b_about

disjoint

disjoint

:bt_about

:about

:r_about

:nm_about

:n_about

:nt_about

disjoint

disjoint

Mappings as OWL Classes

•  A mapping class: – Classifies resources annotated using one vocabulary, and

–  Infers annotaTons using the other vocabulary – … it may be directed


:cm_about

:em_about

:bm_about :rm_about

:b_about

disjoint

disjoint

:bt_about

:about

:r_about

:nm_about

:n_about

:nt_about

disjoint

disjoint

Fig. 2. Redefinition of SKOS relations using :about.

follows:

ex:AO Mapping ≡ :about value lv:animal � :about value lv:company �:about value lv:dangerous action

� :d about value tv:animal � :d about value tv:animal owner �:d about value tv:damage

Admittedly, this mapping is quite unrestricted as it triggers even for resourcesannotated with concepts that only have a skos:related relation with the conceptsof the restriction. It is easy to see how the more specific relations of Figure 2 canbe used in the class axiom to further restrict the applicability of the mapping.

The mapping is directed since a resource annotated with the legal concepts ofex:AO Mapping will not be classified as an instance of that class. The directioncan be reversed by swapping the subclass and equivalent class restrictions onannotations. Furthermore, two annotations can be defined as equivalent by usingonly equivalent class restrictions. There is of course no restriction on the use ofadditional OWL 2 expressions in the class axiom. However, for the mappingit makes no real sense to use a union in the equivalent class restriction: thiswill not lead to new (known) :d about relations between matching resourcesand concepts. One step further is the possibility to exclude resources from amapping where they are annotated using some concept. This can be done byintroducing the complement of a value restriction in the equivalent class axiomof a mapping. However, because of the open world assumption this does notmean that resources that are not annotated will be members of the mappingclass: this requires explicit negative property assertions on the :d about property(thankfully available in OWL 2).

Example


lv:horse

lv:riding_school

lv:kick

:ao_example

:d_about

:d_about

:d_about

tv:animal

tv:animal_owner

lv:animal

lv:company

lv:dangerous_action

skos:broader

skos:broader

skos:broader tv:damage

:AO_Example

rdf:type

:d_about

:d_about

:d_about

:about

:about

:about

Discussion

•  Extensible –  Any OWL axiom may be used in a mapping (e.g. someValuesFrom etc.)

–  Reusable (parTal) mappings –  Exclude resources annotated with a parTcular concept

•  NegaTve property asserTons •  Novel –  “ReificaTon” wrt. normal OWL ontologies

•  Overcomes limitaTons of SKOS semanTcs – Makes explicit the extensional perspecTve that underlies SKOS semanTcs

–  Non-‐intrusive


Discussion

•  OWL 1 vs OWL 2 – Property chains – Disjoint properTes – NegaTve property asserTons

•  The bad – Cannot enforce that the mapping holds between two disTnct concept schemes

– Property chains are not equivalent to super property


Future Work

•  Apply BestMap to other domains –  Legal assessment based on spaTal plans – …

•  Further development of BestPortal – Do the mappings actually work? –  Structured mappings

•  (case frames)

– Does BestPortal really improve access to court proceedings?

–  Connect to the linked data cloud


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