Using linked data in a heterogeneous sensor web: Challenges, experiments and lessons learned

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

Imaginations unbound

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


Objective: Data Integration in a Virtual Environmental Observatory


WaterML

Outline



A Simplified View of Linked Data

•  Obtain sensors and observation data from sensors in Illinois


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.


Workflow of Publishing and Consuming Linked Data


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


Republishing Data to RDF (2)


provenance

rdf:type

Outgoing link

Using Multiple Ontologies


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).


Creating Links by Geometric Analysis (2)


Provenance in Linked Data

•  Where did the data come from? How were they processed?

•  Using Open Provenance Model (OPM)


<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



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.


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


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



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


Outline



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.


Future Work

•  Towards Linked Geostreaming Data •  Tuning the performance •  Facilitating searching and crawling of Linked data •  End-to-end provenance management



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

Using linked data in a heterogeneous sensor web: Challenges, experiments and lessons learned

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