Sensor Data and Semantic Mashups ESWC 2011 Tutorial
Sensor Data and Semantic Mashups ESWC 2011 Tutorial 29th May 2011 Speaker: Kevin Page Context Sensor Network Applications Middleware
Larger, Larger, more more detailed detailed and and sophisticated sophisticated applications applications are are not not the
the focus focus of of this this presentation presentation Sensor Data and Semantic Mashups How can we incorporate sensor data in quick, easy to write, web applications and mashups? How can we take advantage of semantic sensor networks when doing this?
How can we link to and from other useful semantic data sources? Is Is the the surf surf any any good good today? today? Were Were can can II park?
park? Will Will my my car car be be safe safe there? there? Where Where can can II get get tea, tea, cake,
cake, beer(!) beer(!) afterwards? afterwards? Context Applications Web APIs and Linked Data
Semantic Mashups Structure of the tutorial REST and Linked Data APIs An API for Sensor Observations Writing an example mashup REST and Linked Data APIs General Principles REST
everything is a resource which is addressable resources have multiple representations relationships between resources are expressed through hyperlinks all resources share a common interface with a limited set of operations client-server communication is stateless. Linked Data use URIs as names for things use HTTP URIs so that people can look up
those names when someone looks up a URI, provide useful information, using the standards (RDF*, SPARQL) include links to other URIs, so that they can discover more things Commonalities The Primacy of Resources Identification of resources is the key abstraction in REST and RDF where it is also the means to express relationships
Linking is not optional Links to other URIs to discover more things (Linked Data); and as the engine of application state (REST) Segregation of Semantics Semantics have their place (and it's not in the resource addressing/URIs) Adaptability Both approaches can evolve over time REST: state transitions can be changed by modifying the links returned by representations
modifying the hyperstructure Linked Data: assertions about the same resource can be made at different times, in different places, using different ontologies modifying the hyperstructure Differences or complementarity? Model or API What purpose are the commonalities put to? Resources and their relationships are used to:
REST: identify data and transition to other resources; the means to develop an application; an API Semantic Web: encapsulate the underlying data model; link to more related data using the model Domain Driven Design Both the information model and API design are driven by the domain requirements This focuses differentiation and complexity where it should be: around those issues specific to the domain
A common model can be shared between the data and the API So Are all Linked Data applications today RESTful? Are there lots of RESTful systems using Linked Data? Tensions Are the remaining differences fundamental
mismatches or artefacts of current use? SPARQL Content negotiation Information and non-information resources 303 overhead REST and Linked Data: in summary
REST and Linked Data are complementary in the domain but there are important differences especially model vs. API They present an opportunity to build powerful domain centric systems with a common API and data model
An API for Sensor Observations Context Service Service providing API API API for Sensor
Observations Semantic Mashups Domain Model Observation model from the SSN XG ontology Roots in the OGC O&M data model Consumer (vs. producer) centric
crucial link between observations and more detailed domain concepts Resources Observations our primary resources http://id.semsorgrid.ecs.soton.ac.uk/observations/cco/boscombe/Hs/20110101#140500
can be very dependent on the data set or service Collections of Observations e.g. All measurements of wave height in the last hour; all measurements of wind speed from the Boscombe sensor http://id.semsorgrid.ecs.soton.ac.uk/observations/cco/boscombe/Hs/20110101 Remember, there are no accessible semantics in the URIs!
Representations RDF (Observations) O&M GML XML (OGC)
SOS GetObservation() & Xlinks HTML WFS GML XML (OGC) Primary representation,
also sent to a triplestore for SPARQL querying OGC compatibility GeoJSON ? Web API extensions
/latest : within each observation collection next and previous for each observation and collection Links from constituent observations and collections to broader collections (up) /summary: for each collection, max/min values, frequencies, averages, units of measurements, descriptive metadata /sensors: collections for sensors too
Services to provide APIs (briefly) Context Service Service providing API API
API for Sensor Observations Semantic Mashups High-Level API for Observations service Questions? (before the hands-on) Kevin Page University of Southampton [email protected]
Huge thanks to the Southampton SemSorGrid4Env team: Alex Frazer Bart Nagel Kirk Martinez Context Service Service providing API API
API for Sensor Observations Semantic Mashups Hands-on objectives To demonstrate different ways of accessing, navigating, and linking the observation data
Retrieving and manipulating RDF representations Following links for RESTful applications Querying the Observation API using SPARQL Bridging to other Linked Data sources Using latitude & longitude Using a named position
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