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Aggregating Linked Sensor Data
Christoph Stasch, Sven Schade, Alejandro Llaves, Krysztof Janowicz, Arne Bröring
Institute for GeoinformaticsWestfälische Wilhelms-Universität Münster
3rd Workshop on Semantic Sensor NetworksBonn, 2011
Christoph Stasch – [email protected]
Aggregation in Linked Sensor Data
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Adding new links:Belongs the observation value to that feature?
Spatial Aggregation
15,5°CLinking the aggregatedobservation
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Aggregation• Aggregation:
• An aggregation process computes a value, an aggregate, for a group of attribute values by means of an aggregation function. The attribute values are grouped by a partitioning predicate.
• Aggregation Function: • Function used to compute the aggregate.
• Partitioning Predicate: • Predicate used to group objects before aggregating the
values attached to these objects.
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Spatio-temporal vs. Thematic Aggregation
• Spatio-temporal Aggregation: – Partitionining predicate is spatial and/or temporal
• Thematic Aggregation:– Partitioning predicate operates on attribute values
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Linked Sensor Data• World Wide Web is for websites /
documents– HTTP– HTML– ...
• Sensor Web is for sensors– SOS– O&M– ...
• Linked Data Web is for linked data– RDF
• Linked Sensor Data (e.g. Page 2009)
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RESTful SOS Proxy• Proxy service for Sensor Observation Services• Linked data model + URI scheme for observation
resources
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Janowicz, K., Bröring, A., Stasch, C., Schade, S., Everding, T., and Llaves, A. (2011): A RESTful Proxy and Data Model for Linked Sensor Data. International Journal of Digital Earth. DOI:10.1080/17538947.2011.614698, pp. 1-22
Spatio-Temporal Aggregation Service(STAS)
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Stasch, C., Autermann, C., Foerster, T., Pebesma, E.: Towards a Spatiotemporal Aggregation Service in the Sensor Web. Poster Presentation. In: The 14th AGILE International Conference on Geographic Information Science. (2011)
Aggregating Linked Sensor Data
• Linked Data Model:– Extending the SSO pattern to allow aggregated
observations
• Effects on Links from and To Observations– How do links change during aggregation?
• Provenance– Information is contained in Linked Data Model; can be
mapped to Open Provenance Model or Provenance Vocabulary
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Effects on Links from and to Observations
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Spatial Aggregation
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Provenance Information• Common approaches:
– Open Provenance Model• Nodes and edges to define provenance graphs
– Provenance Vocabulary
• Provenance in Sensor Data:– Information about the source of the data as well as
transformations applied– Approaches
• Provenance in Linked Sensor Data• Using OPM for sensor data• Defining own provenance models
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Provenance
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DUL = Dolce Ultra Lightldm = Linked Sensor Data Modelopmv = Open Provenance Model Vocabularyprv = Provenance Vocabulary
Conclusions• Aggregation helps:
– Establishing new links– Fusing datasets
• Extended SSO pattern– Allows for aggregated observations and aggregation
processes– Retracing aggregated Observations back to original
observations mapping to OPM and Provenance Vocabulary
• Effects of aggregation on links from and to observations
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Outlook• Formalize effects of aggregation on links• Enable Spatio-temporal Aggregation Service for
linked sensor data• Integrate with approaches for sensor plug‘n‘play
and linked sensor streams• Utilize semantics of aggregation processes• Integrate uncertainty/quality information
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Discussion• To what aggregation level can we speak of
observations?• Virtual sensors vs. Physical Sensors?• Common aggregation mechanisms in Linked
Data?
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Thank you!
RESTful SOS:http://52north.org/communities/sensorweb/clients/OX_RESTful_SOS/index.htm
STAS:
https://wiki.aston.ac.uk/foswiki/bin/view/UncertWeb/Spatio-temporalAggregationService
http://www.uncertweb.org
http://www.envirofi.org
http://www.envision-project.eu
http://irtg.ifgi.de
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