Linked Data Practices for the Geospatial Community
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Transcript of Linked Data Practices for the Geospatial Community
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Linked Data Practices for the Geospatial Community
Talk subtitle
Presented at GEOSS Workshop on ClimateBoulder Colorado, 23 September 2011Stephan Zednik, [email protected] / Tetherless World Constellation
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Value Proposition of Linked Data
• Discover– Web resources ‘easy’ to generate and link to
• Access– Leverage HTTP methods
• Integrate– RDF is a standard mechanism for specifying the existence
and meaning of connections between items described in the data
• Use– Web standards for data access and representation simplify
data consumption while providing (extreme) expressivity
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Principles of Linked Data
There are 4 principle expectations (rules) for Linked Data
1. Use URIs as names for things
2. Use HTTP URIs so that people can look up those names
3. When someone looks up a URI, provide useful information, using the standards (RDF*, SPARQL)
4. Include links to other URIs, so that they can discover more things
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World Wide Web of Data!
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Linked Data Languages
• SKOS (Simple Knowledge Organizational System)– Thesauri, Taxonomies, Topical Hierarchies
• RDFS (RDF Schema)– Vocabularies
• OWL (Web Ontology Language)– Ontologies
• RDFS+– RDFS + Subset of OWL
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Reuse
• Key factor in re-usability of data: structure
• Regular and structured is– Easier to find– Easier to make tools for– More likely to be referenced
• and therefore beneficiary of network effect
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Re-use Concerns
• Usage & Uptake• Maintenance & Governance• Coverage• Expressivity• Modularity
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Example: SWEET 2 Dependency Graph
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Finding Vocabularies
• No current definitive directory to find existing vocabularies– SchemaWeb, SchemaCache, Swoogle
• Statistics on usage of vocabularies in the wild– Section 2.3 of the State of the LOD Cloud– http://lod-cloud.net/state#terms
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Using Vocabularies
• If suitable terms are found, they should be re-used– Maximizes potential for consumption– Network effect on re-used vocabulary
• New terms should be mapped to well-established existing vocabularies– Standards bodies useful to establish &
promote vocabularies – Network effect long-term driving factor
• Example: FOAF
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W3C Geo Vocabulary
• Basic RDF vocabulary that provides a namespace for representing latitude, longitude, and other spatially located things using WGS84 as a reference datum– http://www.w3.org/2003/01/geo/– Wide usage, but far too simple for GIS tools
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#"> <geo:Point> <geo:lat>55.701</geo:lat> <geo:long>12.552</geo:long> </geo:Point></rdf:RDF>
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OGC GeoSPARQL
• Includes– RDF/OWL Vocabulary for representing
spatial information– A set of functions for spatial computations– A set of query transformation Rules
• Expressivity for GIS tool requirements• http://www.opengeospatial.org/projects/
groups/geosparqlswg
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OGC GeoSPARQL RDF
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Discovering Linked Data
• ‘Standard’ discovery of linked data is via other linked data…
• OpenSearch– Version 1.1 Geo extension (very basic)– Semantics?
• DataCasting– ProductCasting– InventoryCasting
• ServiceCasting
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Querying Linked Data
• SPARQL Endpoint– Requires understanding of structure– Generally domain agnostic
• Faceted Browsing– Pelorus
• http://clarkparsia.com/pelorus– S2S
• http://tw.rpi.edu/web/project/sesf/workinggroups/s2s
• Supports Widgets
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SPARQL Endpoint Web Browser
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Pelorus
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S2S Faceted Browser
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Services & Linked Data• SOAP Web Services and Linked Data are not
complementary– Document exchange vs Web of Data– SOAP ignores HTTP access semantics
• REST (Representational State Transfer)– HTTP as a mechanism for retrieval of resource
representations exposed via URIs– Resource Orientated Architecture (ROA)– Stateless interactions
• Linked Data and RESTful services can be complementary– Will take care in design
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References• Tom Heath and Christian Bizer (2011) Linked Data: Evolving
the Web into a Global Data Space (1st Edition) Synthesis Lectures on the Semantic Web: Theory and Technology, 1:1, 1-136. Morgan & Claypool.– DOI: 10.2200/S00334ED1V01Y201102WBE001– http://linkeddatabook.com/editions/1.0/
• GeoSPARQL SWG– http://www.opengeospatial.org/projects/groups/geosparqlswg
• JPL Datacasting– http://datacasting.jpl.nasa.gov/
• Pelorus– http://clarkparsia.com/pelorus
• S2S– http://tw.rpi.edu/web/project/sesf/workinggroups/s2s