1SSO 1st Nov, 2011

Applying WCO Ontology to Geospatial Web Coverage Services

Xia Wang and Peter Baumann

xia.wang@jacobs-university.de

Jacobs University Bremen, Germany

2SSO 1st Nov, 2011

Outline

• Introduction

• Motivation

• Web Coverage Ontology (WCO)

• Applying WCO to Geospatial Web Coverage Services

• Conclusion

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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.

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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

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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

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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

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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

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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

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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

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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.

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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

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WCO: concept Coverage

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WCO: concept GridCoverage

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WCO: GridCoverage Instance

(b)

(a)

(c)

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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.

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WCO: more complex web coverage

to define application related web coverage

to define complex geometric web coverage

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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

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WCO: interoperation

• Support WCS and WCPS standards

• Support WCS services interoperation

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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

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Thank you!