using linked data in a heterogeneous sensor web: challenges, experiments and lessons learned
DESCRIPTION
Presentation by Liang Yu during the Sensor Web Ontology and Semantics paper session of the Sensor Web Enablement workshop (held during the 2011 Cybera Summit).TRANSCRIPT
National Center for Supercomputing Applications University of Illinois at Urbana-Champaign
Using Linked Data in a Heterogeneous Sensor Web: Challenges, Experiments and Lessons Learned Liang Yu and Yong Liu {liangyu, yongliu}@ncsa.illinois.edu
Outline
Ø Motivation and Goal Ø Using Linked Data for Integration Ø Services for Consuming Linked Data Ø An Example: Visualization Ø Conclusion and Future Work
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Motivation
• Interoperability as a grand challenge in a Virtual Environmental Observatory • The need to integrating different sensor data, citizen sensing,
and other geospatial data etc. • e.g., all river gage height values from all gages in Illinois
between 1st May and 3rd May 2011.
• A heterogeneous Sensor Web is a reality • Different protocols and formats, unknown semantics and no
links.
• A paradigm shift: using Linked Data to build a Linked Sensor Web • Linked data has the potential to provide a solution: URI naming
system, HTTP protocol, RDF, links to other resources. • E.g. an OGC SOS usually has no links to other resources
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Objective: Data Integration in a Virtual Environmental Observatory
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WaterML
Outline
Ø Motivation and Goal Ø Using Linked Data for Integration Ø Services for Consuming Linked Data Ø An Example: Visualization Ø Conclusion and Future Work
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A Simplified View of Linked Data
• Obtain sensors and observation data from sensors in Illinois
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Illinois States Sensors in Illinois
Data Stream
http://sensorweb.ncsa.uiuc.edu/data/map/state/USGS/ Illinois
http://sensorweb.ncsa.uiuc.edu/api/sensordata/sites?within=http://sensorweb.ncsa.uiuc.edu/data/map/state/USGS/Illinois
http://sensorweb.ncsa.uiuc.edu/api/sensordata/observations?observedBy.within=http://sensorweb.ncsa.uiuc.edu/data/map/state/USGS/Illinois
Key Challenges
• Publishing Linked Data • Re-publishing existing plain data to semantically linked data. • Linking potentially “linkable data” together and enabling complex
queries in a heterogeneous Sensor Web.
• Consuming Linked Data • Serving data in an OGC RESTful SOS-like service. • Tracking the provenance of Linked Data to facilitate trust and
validation.
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Workflow of Publishing and Consuming Linked Data
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Ontology
Geometric Analysis
Linked Data
LDA
Tools
Raw Data Linked Data
Republishing Data to RDF (1)
• Use XML as an intermediate format • All non-XML data (Shapefile, Excel) are transformed to XML.
• Use XSLT to convert intermediate XML to RDF/XML • Three different annotations are implemented in XSLT
• semantic annotation (rdf:type) • outgoing links (to DBPedia), and • provenance.
• Both syntactic transformations and semantic annotations are performed
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Republishing Data to RDF (2)
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provenance
rdf:type
Outgoing link
Using Multiple Ontologies
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Creating Links by Geometric Analysis (1)
• To discover and create links between entities based on their spatial attributes. • Different from previous work
• E.g.: http://www4.wiwiss.fu-berlin.de/bizer/silk/
• Tools: Geotools (Java).
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Creating Links by Geometric Analysis (2)
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Provenance in Linked Data
• Where did the data come from? How were they processed?
• Using Open Provenance Model (OPM)
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<ssn:observedBy rdf:resource="http://sensorweb.ncsa.uiuc.edu/data/sensordata/sites/CUAHSI/NWIS/03339000"/> <opmo:wasDerivedFromStar rdf:resource="http://waterservices.usgs.gov/nwis/iv"/>
Sensor
Observation opmo:wasDerivedFromStar
opmo:wasDerivedFromStar
ssn:observedBy opmo:WasGeneratedBy
Outline
Ø Motivation and Goal Ø Using Linked Data for Integration Ø Services for Consuming Linked Data Ø An Example: Visualization Ø Conclusion and Future Work
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Developing SOS with Linked Data API (1)
• An OGC RESTful SOS-like service over the integrated linked data • Can be accessed by simple URLs. • Is as flexible as SPARQL but with simpler syntax.
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q Feature of Interest (http://sensorweb.ncsa.uiuc.edu/data/map/watershed/USGS/2009_0)
q Single sensor site (http://sensorweb.ncsa.uiuc.edu/data/sensordata/sites/CUAHSI/EPA/MWRDSTOR:WW_39)
q Collection of sensor sites (http://sensorweb.ncsa.uiuc.edu/api/sensordata/sites)
q Single observation (http://sensorweb.ncsa.uiuc.edu/data/event/hail/noaa/2010/10908_2010-12-31T22:40:00)
q Collection of observations (http://sensorweb.ncsa.uiuc.edu/api/sensordata/observations)
Developing SOS with Linked Data API (2) • Obtain all the sensor sites within Illinois state.
• http://sensorweb.ncsa.uiuc.edu/api/sensordata/sites?within=http://sensorweb.ncsa.uiuc.edu/data/map/state/USGS/Illinois
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items": [ {"_about": "http://sensorweb.ncsa.uiuc.edu/data/sensordata/sites/CUAHSI/EPA/MWRDSTOR:WW_39", "hasCode": "MWRDSTOR:WW 39", "hasLocation": {
"lat": 41.88185119628906, "long": -87.63558197021484, "type": "http://www.w3.org/2003/01/geo/wgs84_pos#Point"}, "hasName": "South Branch Chicago River @ Madison St.", "hasNetwork": "http://sensorweb.ncsa.uiuc.edu/data/sensordata/network/CUAHSI/EPA", "hasStream": "http://sensorweb.ncsa.uiuc.edu/api/sensordata/observations?observedBy=http://sensorweb.ncsa.uiuc.edu/data/sensordata/sites/CUAHSI/EPA/MWRDSTOR:WW_39", "type": "Sensor", "wasDerivedFromStar": "http://water.sdsc.edu/waterOneFlow/", "within": ["http://sensorweb.ncsa.uiuc.edu/data/map/county/USGS/Cook_County,_IL","http://sensorweb.ncsa.uiuc.edu/data/map/state/USGS/Illinois","http://sensorweb.ncsa.uiuc.edu/data/map/watershed/USGS/2009_2627"]},
Outline
Ø Motivation and Goal Ø Using Linked Data for Integration Ø Services for Consuming Linked Data Ø An Example: Visualization Ø Conclusion and Future Work
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An Example Application (Visualization of SOS Results) • Visualization Platform: WWT (World Wide Telescope)|Earth • Sensor Data: river gage height values produced by gages in Illinois between
2011-05-01 and 2011-05-03. q http://sensorweb.ncsa.uiuc.edu/api/sensordata/observations?observedBy.within=http://
sensorweb.ncsa.uiuc.edu/data/map/state/USGS/Illinois&_sort=observationResultTime.inXSDDateTime&min-observationResultTime.inXSDDateTime=2011-05-01T00:00:00-05:00&_page=0&max-observationResultTime.inXSDDateTime=2011-05-03T00:00:00-05:00&observedProperty=http://sensorweb.ncsa.uiuc.edu/data/property/USGS/NWIS:UnitValues/00065
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Outline
Ø Motivation and Goal Ø Using Linked Data for Integration Ø Services for Consuming Linked Data Ø An Example: Visualization Ø Conclusion and Future Work
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Conclusion
• A “Linked Sensor Web” solution for integrating heterogeneous sensor data sources and geospatial data. • A best practice of using W3C SSN ontology as well as other
domain ontologies. • A method to discover and create links among spatial data. • Using Linked Data API to provide OGC RESTful SOS-like
services • http://sensorweb.ncsa.uiuc.edu/api-list.html
• Tracking provenance data and managing them using OPM.
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Future Work
• Towards Linked Geostreaming Data • Tuning the performance • Facilitating searching and crawling of Linked data • End-to-end provenance management
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Acknowledgements
Ø Microsoft Research Connections Ø “Environmental Informatics” Program
Ø Institute for Advanced Computing Applications and Technologies at the University of Illinois at Urbana-Champaign Ø “Virtual Observatory for Sustainability of Intensively Managed
Environmental Systems” Project