Using RDF/OWL Technologies for Discovery and Use Metadata

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Using RDF/OWL Technologies for Discovery and Use
Metadata
M.Benno Blumenthal, Michael Bell, John del
Corral, and Emily Grover-KopecInternational
Research Institute for Climate and
SocietyColumbia Universityhttp//iridl.ldeo.co
lumbia.edu/
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Definitions

• Resource Description Framework (RDF)
• Web Ontology Language (OWL)

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Why RDF?

• Web-based system for interoperating semantics
• A key part of the Semantic Web
• RDF/OWL is an interesting technology, but it is
  even more interesting when it is clear that it
  can help solve our problems

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The Data Problem
Datasets
Users
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The Tool Interface
Datasets
Tools
Users
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Standard Metadata
Standard Metadata Schema/Data Services
Datasets
Tools
Users
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Many Data Communities
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Super Schema
Standard metadata schema
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Super Schema direct
Standard metadata schema/data service
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Flaws

• A lot of work
• Super Schema/Service is the Lowest-Common-Denomina
  tor
• Science keeps evolving, so that standards either
  fall behind or constantly change

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RDF Standard Data Model Exchange
Standard metadata schema
RDF
RDF
RDF
RDF
RDF
RDF
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RDF Data Model Exchange
Standard metadata schema
RDF
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RDF Architecture
Virtual (derived) RDF
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Why is this better?

• Maps the original dataset metadata into a
  standard format that can be transported and
  manipulated
• Still the same impedance mismatch when mapped to
  the least-common-denominator standard metadata,
  but
• When a better standard comes along, the original
  complete-but-nonstandard metadata is already
  there to be remapped, and late semantic binding
  means everyone can use the new semantic mapping
• Can uses enhanced mappings between models that
  are close
• EASIER these are tools to enhance the mapping
  process

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Sample Tool Faceted Search
http//iridl.ldeo.columbia.edu/ontologies/query2.p
l?...
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Distinctive Features of the search

• Search terms are interrelated
• terms that describe the set of returns are
  displayed (spanning and not)
• Returned items also have structure (sub-items and
  superseded items are not shown)

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Architectural Features of the search
http//iridl.ldeo.columbia.edu/ontologies/query2.p
l

• Multiple search structures possible
• Multiple languages possible
• Search structure is kept in the database, not in
  the code

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Cast of RDF Characters
Semantic Layers Query Language Tools and Frameworks
SPARQL Protégé
RDFS SeRQL
OWL Sesame
SKOS Reasoners Redland
SWRL Jena
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RDF framework for writing connections

• Triplets of
• Subject
• Property (or Predicate)
• Object
• URIs identify things, i.e. most of the above
• Namespaces are used as a convenient shorthand for
  the URIs

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Datatype Properties

• WOA dctitle NOAA NODC WOA01
• WOA dcdescription NOAA NODC WOA01 World
  Ocean Atlas 2001, an atlas of objectively
  analyzed fields of major ocean parameters at
  monthly, seasonal, and annual time scales.
  Resolution 1x1 Longitude global Latitude
  global Depth 0 m,5500 m Time Jan,Dec
  monthly

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Object Properties
WOA iridlisContainerOf Grid-1x1, Grid-1x1
iridlisContainerOf Monthly
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WOA01 diagram
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Standard Properties

• WOA dctermhasPart Grid-1x1,
• Grid-1x1 dctermhasPart MONTHLY
• Alternatively
• WOA iridlisContainerOf Grid-1x1,
• iridlisContainerOf rdfssubPropertyOf
  dctermhasPart

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netcdf/CF in RDF
SST rdftype cfattnon_coordinate_variable,
SST cfattstandard_name cfsea_surface_tempera
ture, SST netcdfhasDimension longitude

• Object properties provide a framework for
  explicitly writing down relationships between
  data objects/components, e.g. vague meaning of
  nesting is made explicit
• Properties also can be related, since they are
  objects too

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Noncontextual Modeling

• noncontextual modeling make RDF the perfect glue
  between systems and fixed data models The
  Semantic Web

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RDF Level

• Transport/Exchange (RDF/XML)
• Storage
• RDF APIs (Redland,Jena,Sesame)
• Query (SPARQL,SeRQL, )
• Basic Semantics

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RDF SemanticsRDF Primer
Truly useful property rdftype a
Underlying Class rdfProperty
Organizational Classes rdfBag rdfAlt rdfSeq rdfList
Structured values rdfvalue
Reification rdfStatement rdfsubject rdfpredicate rdfobject
Bag Properties rdf_1 rdf_2
List Properties rdffirst rdfrestrdfnil
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RDF-Schema (RDFS)
Transitive Properties rdfssubClassOf (is a), rdfssubPropertyOf
rdfsClass, rdfsResource
rdfsmember rdfsdomain, rdfsrange
rdfsDatatype, rdfsLiteral, rdfsContainer
Refering to other RDF documents rdfsseeAlso, rdfsisDefinedBy
Basic documentation rdfslabel, rdfscomment
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Gazetteer Classes
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Gazetteer Individuals
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Search Interface Term

• http//iri.columbia.edu/benno/sampleterm.pdf

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Semantics lead to Virtual Triples

• Transitive
• a rdfssubClassOf b rdfssubClassOf c
• implies a rdfssubClassOf c
• i.e. semantics of rdfssubClassOf imply
  additional triples not explicitly stated
• Likewise
• a rdfssubPropertyOfb rdfssubPropertyOf c
• implies a rdfssubPropertyOf c
• More interestingly,
• a myprop b, myprop rdfssubPropertyOf
  prop2 implies a prop2 b

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Subcategories are not subClasses

• So carelessly translating existing conceptual
  organizations can get one into trouble

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Domain and Range are inherited

• Since the domain and range of a property are
  classes, then subclasses inherit properties (in
  this sense)

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UML/RDFS

• Unified Modeling Language
• Base concepts are the same (RDFS lacks methods),
  so one can export the underlying structure of the
  code as the underlying structure for the metadata
• See Representing UML in RDF

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Ontologies

• Use Conventions to connect concepts to
  established sets of concepts
• Generate additional virtual triples from the
  original set and semantics
• RDFS some property/class semantics
• OWL additional property/class semantics more
  sophisticated (ontological) relationships

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OWL

• Language for expressing ontologies, i.e. the
  semantics are very important. However, even
  without a reasoner to generate the implied RDF
  statements, OWL classes and properties represent
  a sophistication of the RDF Schema
• However, there is a serious split in world view
  from what we have been talking about concepts as
  classes vs concepts as individuals

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OWL
rdfProperty owlDatatypeProperty owlObjectProperty owlAnnotationProperty
owlFunctionalProperty owlInverseFunctionalProperty owlTransitiveProperty owlSymmetricProperty
rdfsseeAlso owlimports
owlontology
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Protégé

• Tool for editing/displaying Ontologies
• Different tabs display different perspectives
• http//protege.stanford.edu/

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Cast of RDF Characters II
Semantic Layers Query Language Tools and Frameworks
SPARQL Protégé
RDFS SeRQL
OWL Sesame
SKOS Reasoners Redland
SWRL Jena
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Query Language SPARQL

• (quick reference at http//www.dajobe.org/2005/04-
  sparql/)
• Supported by Redland, Jena, Sesame-2.0 (alpha)
• Jena implementation supports url source of
  triples, i.e. do not even need a triple store
• The standard

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Query Language SeRQL

• Older than SPARQL
• Implemented on top of Sesame
• Currently more powerful than SPARQL, i.e. has
  nested queries

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SeRQL DetailsCopied from on-line tutorial

• Syntax
• Select
• Construct
• Where
• From

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SeRQL basic syntax

• person fooworksFor Company rdftype
  fooITCompany

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SeRQL multiple statements

• subj1 pred1 obj1 pred2 obj2
• Or
• subj1 pred1 obj1 , subj1 pred2 obj2

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SeRQL short cuts

• subj1 pred1 obj1,obj2,obj3
• (also implies obj1,obj2,obj3 are distinct)

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SeRQL Select
Output as table (XML)

• SELECT dataset, dlabel
• FROM dataset rdftype iridldataset,
• dataset rdfslabel dlabel
• USING NAMESPACE
• iridl lthttp//iridl.ldeo.columbia.edu/ontologie
  s/iridl.owlgt

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SeRQLConstruct
Output as RDF (RDF/XML)
CONSTRUCT dataset rdftype fooLabelledDatasets
FROM dataset rdftype iridldataset
rdfslabel dlabel USING NAMESPACE iridl
lthttp//iridl.ldeo.columbia.edu/ontologies/iridl.o
wlgt
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Faceted Search Explicated
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Search Interface

• Items (datasets/maps)
• Terms
• Facets
• Taxa

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Search Interface Semantic API

• item dctitle dcdescription rsslink
  iridlicon
• dctermisPartOf item2
• dctermisReplacedBy item2
• item trmisDescribedBy term
• term a facet of taxa of trmTerm,
• facet a trmFacet, taxa a trmTaxa,
• term trmdirectlyImplies term2

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Faceted Search w/Queries
http//iridl.ldeo.columbia.edu/ontologies/query2.p
l?...
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RDF Architecture
Virtual (derived) RDF
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IRI RDF Architecture
Data Servers
MMI
Ontologies
JPL
Start Point
bibliography
Standards Organizations
RDF Crawler
Location Canonicalizer
RDFS Semantics Owl Semantics SWRL Rules SeRQL
CONSTRUCT
Time Canonicalizer
Sesame
Search Queries
Search Interface
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Creating Virtual Triples from Semantic Layers
Semantic Layers Query Language Tools and Frameworks
SPARQL Protégé
RDFS SeRQL
OWL Sesame
SKOS Reasoners Redland
SWRL Jena
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SWRL

• SWRL A Semantic Web Rule Language Combining OWL
  and RuleML
• A language for writing rules in RDF/OWL, i.e. RDF
  statements that are rules for creating new RDF
  statements

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Simple Knowledge Organization System (SKOS)

• Schema for relating concepts

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Simple Knowledge Oranization System (SKOS)

• So, for a resource of type skosConcept, any
  properties of that resource (such as creator,
  date of modification, source etc.) should be
  interpreted as properties of a concept, and not
  as properties of some 'real world thing' that
  that resource may be a conceptualisation of.
• This layer of indirection allows thesaurus-like
  data to be expressed as an RDF graph. The
  conceptual content of any thesaurus can of course
  be remodelled as an RDFS/OWL ontology. However,
  this remodelling work can be a major undertaking,
  particularly for large and/or informal thesauri.
  A SKOS Core representation of a thesaurus maps
  fairly directly onto the original data
  structures, and can therefore be created without
  expensive remodelling and analysis

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RDF Frameworks
Protégé API
Redland Bindings in many languages, supports several triple stores, some with context
Jena Java API, some cmd line utilities, supports inference layers
Sesame HTTP server, Java API, supports inference, version 2 alpha has context
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Sesame

• SAIL- Storage and Inference Layer
• i.e. you can write down rules that imply virtual
  triples so that triples are generated as they are
  put into the store

RDF No inference
RDFS RDFS inference
OWLIM Some OWL inference
Custom
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Jena

• Java framework
• In-memory and persistent stores
• Inference API

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Topics/Issues

• OpenDAP and RDF can we transport data semantics
  without fixing the entire schema?
• netcdf/HDF and RDF do we need non-contextual
  modeling in our metadata transport/storage?
• Concepts as classes vs concepts as individuals
• Sub-classes vs sub-categories
• OWL in detail
• Protégé demo

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RDF Cast of Characters
Semantic Layers Query Language Tools and Frameworks
SPARQL Protégé
RDFS SeRQL
OWL Sesame
SKOS Reasoners Redland
SWRL Jena