OGC 08-094r1 SWE Common Data Model
It is not recommended to use the concepts of “description” and “label” in a way that they contain robust semantic information i.e. that machines can rely upon. The content of
such fields is intended to be interpretable solely by humans.
6.3.2 Robust semantics
All SWE Common data types allow for associating each data component in a dataset with the definition of the Property that it represents.
Requirement
http:www.opengis.netspecSWE2.0reqcoresemantics-defined
Req 7. All data values shall be associated with a clear definition of the property that
the value represents.
It is recommended that a model uses references to out-of-band dictionaries rather than inline information because semantics are supposed to be shared by multiple datasets.
Using references also helps by providing a framework that is independent from the actual semantic technology used.
The SWE Common UML models and XML schemas desribed in this standard can be used in combination with any semantic web technology. It is thus possible to connect a
SWE dataset description to an existing taxonomy provided the external register exposes a unique identifier for each entry.
These semantic references point to out-of-band semantic information that can be encoded in various languages, such as the Ontology Web Language OWL or GML dictionary.
Requirement
http:www.opengis.netspecSWE2.0reqcoresemantics-resolvable
Req 8. If robust semantics are provided by referencing out‐of‐band information, the
locators or identifiers used to point to this information shall be resolvable by some
well ‐defined method.
6.3.3 Time, space and projected quantities
Temporal, spatial and other projected quantities need to be further defined by specifying the reference frame and axis with respect to which the quantity is expressed. In SWE
Common, any simple component type can be associated to a particular axis of a given reference frame.
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Copyright © 2011 Open Geospatial Consortium
SWE Common Data Model OGC 08-094r1
Examples
Satellite location data can be defined as a vector of 3 components, expressed in the J2000 ECI Cartesian frame, the 1
st
component being associated to the X axis, the 2
nd
to the Y axis and the 3
rd
to the Z axis. Angular velocity data from an Inertial Measurement Unit can be defined as a vector of 3 components, expressed in
the plane reference frame for instance ENU defined by local East, North, Up directions, the Euler components being mapped to X, Y, Z respectively.
Relative time data can be given with respect to an arbitrary epoch itself positioned in a well defined reference frame such as TAI from the French “Temps Atomique International” = International Atomic Time.
Requirement
http:www.opengis.netspecSWE2.0reqcoretemporal-frame-defined
Req 9. A temporal quantity shall be expressed with respect to a well defined
temporal reference frame and this frame shall be specified.
Requirement
http:www.opengis.netspecSWE2.0reqcorespatial-frame-defined
Req 10. A spatial quantity shall be expressed with respect to the axes of a well
defined spatial reference frame and this frame shall be specified.
The “Time” class detailed in clause 7.2.9 is designed for carrying a temporal reference frame or a time of reference in the case of relative time data.
The “Vector” class detailed in clause 7.3.2 is a special type of record used to assign a reference frame to all its child-components.
The “Matrix” class defined in clause 7.5.2 allows the definition of higher order tensor quantities.
This standard does not impose requirements on the type of reference frames that a standardization target shall support. Standards that are dependent on this specification can
and often should however define a minimum set of reference frames that shall be supported by all implementations.
6.4 Data Quality
Quality information can be essential to the data consumer and the SWE Common Data Model provides simple and flexible ways to associate qualitative information with each
component of a dataset.
Copyright © 2011 Open Geospatial Consortium
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