1 sso 1st nov, 2011 applying wco ontology to geospatial web coverage services xia wang and peter...
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1SSO 1st Nov, 2011
Applying WCO Ontology to Geospatial Web Coverage Services
Xia Wang and Peter Baumann
Jacobs University Bremen, Germany
2SSO 1st Nov, 2011
Outline
• Introduction
• Motivation
• Web Coverage Ontology (WCO)
• Applying WCO to Geospatial Web Coverage Services
• Conclusion
3SSO 1st Nov, 2011
Introduction
• Textual data & raster (array) data on the (future) Web• e.g., 1-D sensor time series, 2-D maps, 3-D x/y/t satellite image time series and x/y/z
exploration data, 4-D x/y/z/t climate and ocean data, …
• massive multi-dimensional data, ranging into Terabytes, soon Petabytes
• different with the textual data at many levels
• What is raster data? @ ArcGIS
• a raster consists of a matrix of cells (or pixels) organized
into rows and columns (or a grid)
• e.g.,a graphic, where each cell contains a value
representing information, e.g. temperature, humidity, elevation,
Ozone concentration, spectral info.
4SSO 1st Nov, 2011
Sensor, image, statistics data• Life Science: Pharma/chem, healthcare / bio research, bio statistics, genetics
• Geo: Geodesy, geology, hydrology, oceanography, meteorology, earth,space research, ...
• Engineering & research: Simulation & experimental data in automotive/shipbuilding/ aerospace industry, turbines, process industry, astronomy, experimental physics, high energy physics, ...
• Management/Controlling: Decision support, OLAP, data warehousing, census, statistics in industry and public administration, ...
• Multimedia: e-learning, distance learning, ...
Raster Service Application Fields
5SSO 1st Nov, 2011
coverage (services)
• Raster = Coverage in OGC/GIS speak.
• Coverage as a core abstract feature of raster data, denoting some "space-varying phenomenon" by ISO 19123.
• Coverage services are becoming a very important kinds of web applications, especially in the geospatial domain.
• Geography Markup Language (GML) 3.2.1 as a modeling language for geographic systems
6SSO 1st Nov, 2011
WCS 2.0 & WCPS 1.0
• Web Coverage Services (WCS) as OGC standard allows to query and retrieve geospatial web coverages
• GetCapability, DescribeCoverage, and GetCoverage
• a WCS request can specify the retrieval by using a few simple operations, e.g., subsetting, cutout (trim), scaling, and
reprojection.
• Web Coverage Processing Services (WCPS) defines a protocol-independent coverage processing language
• allowing clients to send requests of arbitrary complexity for evaluation by the server
• based on the conceptual model of WCS
• submitting QL-style requests for online data navigation and analysis in a set-oriented coverage expression language
• Constructor & condenser
• E.g., deriving the vegetation index, determining statistical evaluations, and generating different kinds of plots, like classification, histograms, etc
7SSO 1st Nov, 2011
Motivation
• Large-scale raster data/apps are increasing sharply• e.g, sensor, (satellite) image, statistics data in earth, space, life, and social sciences
• especially, flexible scalable web services on large(tera/peta-byte), multi-dimensional n-D array (pixel) data
• Current raster services targeted at humans• “portryal”= surfing images, navigating maps
• Raster data & raster web services needs semantics• Web Coverage Services (WCS): provides data + descriptions
• WPS, WPCS, WCS standards syntactically, functionally …
• Web service description, discovery, selection, composition, …
• Ex: Google map
8SSO 1st Nov, 2011
Why Web Coverage Ontology (WCO)?
• WCO provides a formal approach to defined the semantic of web coverage and their features, constraints, relations and so on.
• WCO is designed for machines to digest. It further semantically supports WCS automatic discovery, composition, and interoperation.
What we have done is,• to build a core WCO based on the existing specifications and industry standards
• to keep the WCO as a small scale with good scalability. It can import and reuse other existing domain and application ontologies.
• to evaluate the WCO in geospatial domain, first
9SSO 1st Nov, 2011
Web Coverage formal definition
• A coverage is a function from a spatial, temporal or spatiotemporal domain to an attribute range. A coverage associates a position within its domain to a record of values of defined data types (ISO 19123, 2005).
• A coverage consists of three primary elements: a domain
a range
a mapping function
«Data Type»DataRecordPT
AbstractCoverage+ coverageFunction: gml:CoverageFunction [0..1]+ metaData [0..1]
«Data Type»AbstractFeature
«Union»DomainSet
«Data Type»RangeSet
1
rangeSet
1
1
domainSet
1
1
rangeType
1
From GML 3.2.1
Predefined hook
for metadata
Note:ISO 19123 generic-> many different
implementations possible
«Data Type»
[OGC 09-146r1]
(1,2) (2,2)
(2,1)(1,1)
Domain
3C° 5°C 7°C 11°CRange
(+x, -y) Order
10SSO 1st Nov, 2011
Web Coverage Subtypes
«FeatureType»
AbstractCoverage
MultiSolidCoverage
MultiSurfaceCoverage
MultiCurveCoverage
MultiPointCoverage
DiscreteCoverage
ContinuousCoverage
as per GML 3.2.1
RectifiedGridCoverage
ReferenceableGridCoverageGrid
Coverage
• Coverage may be classified into different types, e.g., quadrilateral grid coverage, Thiessen polygon coverage, segmented curve coverage, and multipoint coverage (ISO19123, 2005)
• Most EO coverages are grid coverage.
11SSO 1st Nov, 2011
WCO: web coverage types
• by geographic phenomena: discrete and continuous
• by the types of domain set: spatial, temporal, spatiotemporal, abstract axis
axis={s,t,aaxis}
e.g., if axis={s,t}, then it is a spatiotemporal;
• by dimension: 1D ~ 5D
or more, |axis|= dim
15SSO 1st Nov, 2011
Apply the WCO to …
• model the complicated or real life web coverages, e.g., ThiessenPolygonCoverage, SegmentedCurveCoverage, …
• semantically classify/index of resources/coverages
• semantically query and retrieving of resources/coverages, and
• support the interoperation of different web coverage services and web coverage process services.
16SSO 1st Nov, 2011
WCO: more complex web coverage
to define application related web coverage
to define complex geometric web coverage
18SSO 1st Nov, 2011
WCO: query examples
test1: ?Coverage[Domain hasValue ?Grid]memberOf Coverage and ?Grid[Dimension hasValue ?dimension]memberOf Grid and ?dimension>=2
test2: ?Point[pos hasValue ?pos,?srsName hasValue ?srsName]memberOf Point and ?pos[et1 hasValue ?et1,et2 hasValue ?et2]memberOf DoulbList
19SSO 1st Nov, 2011
WCO: interoperation
• Support WCS and WCPS standards
• Support WCS services interoperation
20SSO 1st Nov, 2011
Conclusion & Future work
• After formally defined a core WCO Ontology for geospatial web coverage services
• Primarily investigate how to apply the WCO into the related applications
• Future work will focus on the semantic of WCPS operations
• Also on extending the current semantic web technologies to support raster data and data types