Geospatial semantics research at Ordnance Survey Cathy Dolbear, Paula Engelbrecht, John Goodwin, Glen Hart and Ian Holt

Ordnance Survey GeoSemantics research Motivation – why is a mapping agency interested in semantics? Ontology authoring RDF data Semantic data integration Merging ontologies Linking ontologies to relational databases Spatial and semantic reasoning and querying

Ordnance Survey – who we are National Mapping Agency of Great Britain One of the largest geospatial databases concepts Customers use GIS systems & spatially enabled databases to process data

Motivation Ontological representation Benefits to OS Customer benefits Data Mining Data & Product Repurposing Semantic Web Enablement Semi-automated data integration Better Classification Quality Control Time

Ordnance Survey GeoSemantics research Motivation – why is a mapping agency interested in semantics? Ontology authoring RDF data Semantic data integration Merging ontologies Linking ontologies to relational databases Spatial and semantic reasoning and querying

Topographic domain ontology Describes what we as an organisation know Beyond a simple taxonomic classification Provides a framework for specifying product content: What our customers need What can be captured and stored.

Topographic domain ontology Developed Hydrology, Administrative Geography, Buildings and Places ~ 600 concepts, ALCOQ expressivity (OWL 1.1) Every Allotment is owned by exactly 1 Local Authority Working on Addresses, Settlements and Land forms Plus supporting modules: Mereology, Spatial Relations, Network topology.

Conceptual AspectComputational Aspect Our approach to building ontologies Every River Stretch is part of a River River_Stretch direct_part_of River Computational Ontology ConceptualOntology Knowledge represented in a form understandable to people Knowledge represented in a form manipulable by computers

Rabbit: Controlled natural language Structured English, compilable to OWL Intelligible to domain expert Can author conceptual ontology Guides good modelling practice Other domain experts are able to validate the work Acts as documentation for the OWL Part of OWL 1.1 task force to develop a controlled natural language syntax

Ordnance Survey GeoSemantics research Motivation – why is a mapping agency interested in semantics? Ontology authoring RDF data Semantic data integration Merging ontologies Linking ontologies to relational databases Spatial and semantic reasoning and querying

Semantically enabling data - an RDF Gazetteer Experiment to semantically describe gazetteers OWL ontology to describe the concepts RDF version to represent the data Currently includes administrative regions Adding cities and other settlements, addresses etc Adding more topographic relationships Spatial boundary information embedded in the RDF using GML

Oracle RDF Limited expressivity How much do we really need? Benefits likely to be using RDF as a data supply format rather than storage model RDF likely to degrade performance: we have > 10 billion triples Spatial component must be executed after RDF filtering Would it be more efficient to perform the spatial query first to minimise the size of the RDF graph? Problems with pure RDF

Ordnance Survey GeoSemantics research Motivation – why is a mapping agency interested in semantics? Ontology authoring RDF data Semantic data integration Merging ontologies Linking ontologies to relational databases Spatial and semantic reasoning and querying

Semantic data integration VO Data ontology Query: Find all addresses with a taxable value over £500,000 in Southampton OS Buildings and Places ontology VO Domain ontology Valuation Office Data OS Address Layer 2 OS Data ontology Merge

Has Form Education Services School and Premises School Local Authority School Junior School High School Infant School Public & Independent School Private Primary SchoolPrivate Secondary School Ordnance Survey Valuation Office Alignment: currently at data level

Evaluation Assess which concepts from one ontology should be included in another Modularisation Isolate these concepts from the rest of the donor ontology Integration Map and/or adapt the donor module for integration into the receiving ontology. Merging ontologies

Ontologies are never perfect: not a complete descriptions of any domain Automatic tools [PROMPT, FOAM, SWOOP modularisation etc] can help with navigation / suggestion but Domain experts needed to add in their knowledge/ judgement Some concepts are more important than others Need to restrict the referencing of a concept Early stages of research Merging ontologies – some thoughts

Ordnance Survey GeoSemantics research Motivation – why is a mapping agency interested in semantics? Ontology authoring RDF data Semantic data integration Merging ontologies Linking ontologies to relational databases Spatial and semantic reasoning and querying

Semantic data integration VO Data ontology Query: Find all addresses with a taxable value over £500,000 in Southampton OS Buildings and Places ontology VO Domain ontology Valuation Office Data OS Address Layer 2 OS Data ontology Merge

Linking ontologies to databases D2RQ - maps SPARQL queries to SQL, creating virtual RDF [Bizer et al, 2006] No need to convert data to RDF explicitly Modifying the API to: Use OWL-based description of mapping (data ontology) Map queries via spatial relations to SQL spatial operators Use views to reduce number of triples and improve efficiency

Simplified Example: Building Footprint Building House Has Footprint Has Column Is a Has Column Polygon DB Building Theme Topographic Area Table Is a Topographic AreaTable and hasColumn (Theme and (has FieldValue has Buildings)) Domain Ontology Data Ontology Is a Is equivalent to SELECT FID, Theme, Polygon FROM TopographicArea WHERE Theme = Buildings;

More complex example - Islands Every Island is a kind of Land that is surrounded by Water

Ordnance Survey GeoSemantics research Motivation – why is a mapping agency interested in semantics? Ontology authoring RDF data Semantic data integration Merging ontologies Linking ontologies to relational databases Spatial and semantic reasoning and querying

Several options in the literature: Convert OWL reasoner to RCC8 reasoner Connections to link the two logics Concrete domains Trying something simpler – data ontology spatial relationships mapped to Oracle SDO_RELATE operators spatially_inside maps to SDO_INSIDE(, ) = TRUE Spatial and semantic reasoning

Finding Islands Database.owl (Table, Column, Primary Key) SpatialRelations.owl (Inside, Contains, Touches) SELECT ta1.FID, ta1.Theme, ta1.Polygon FROM TopographicArea ta1, TopographicArea ta2 WHERE ta1.Theme = Land' AND ta2.Theme = 'Water' AND SDO_INSIDE(ta1.Polygon, ta2.Polygon) = 'TRUE';

Finding Islands – next steps Database.owl Spatial Relations.owl SELECT ta1.FID, ta1.Theme, ta1.Polygon FROM TopographicArea ta1, TopographicArea ta2 WHERE ta1.Theme = Land' AND ta2.Theme = 'Water' AND SDO_INSIDE(ta1.Polygon, ta2.Polygon) = 'TRUE'; OS spatial database Find me a detached house on an island DL Reasoner RDF

Graph matching using SPARQL Can do SPARQL custom functions for spatial queries Or split the query into spatial (SQL) and semantic (SPARQL) parts? Waiting for conjunctive query language (SPARQL DL) Should knowledge be included in the query or the ontology? How do we make it easier for domain experts to make queries? Spatial and semantic querying

Semantics research often doesnt consider the semantics! Domain experts need to be at the centre of the process Technology transfer is difficult: Benefits of semantics in products and applications must be clarified Conclusions

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