RE: OASIS GML Where profile - teleconference tomorrow

["Carl Reed" <creed@opengeospatial.org>]

In recent discussions with the OGC GML community, we spoke about OASIS requirements. During the discussion I suddenly thought about exploring the possibility of using an existing profile of GML: Simple Features Profile of GML. This is an adopted OGC standard and has been implemented by numerous technology providers. The mapping of types supported in the SF Profile are:

 

GML Geometric Property Type	Equivalent SQL/MM Type
gml:PointPropertyType	ST_Point
gml:CurvePropertyType	ST_LineString.
gml:SurfacePropertyType	ST_Polygon
gml:GeometryPropertyType	ST_Geometry
gml:MultiPointPropertyType	ST_MultiPoint
gml:MultiCurvePropertyType	ST_MultiCurve
gml:MultiSurfacePropertyType	ST_MultiSurface
gml:MultiGeometryPropertyType	ST_GeomCollection

 

The only geometry type missing required by the OASIS community is "CIRCLE", although curve could be used to define a circle. Anyway, the GML gurus said that the circle element could be added by extension, as part of an OASIS application schema based on the SF Profile, or as a change request to GML Simple Features Profile.

 

The Simple Features profile of GML is 100% consistent with the OGC and ISO Simple Features standard. SF-SQL has been implemented by every major database vendor (commercial, commercial open source, and open source). The profile also provides internationalization (multi-language) support.

 

The main potential drawback is that the Profile contains more than just geometry. The Profile also contains the GML Feature model. But this may not be a bad thing if one looks a year or two down the road.

GML defines features distinct from geometry objects. A feature is an application object that represents a physical entity, e.g. a building, a river, or a person. A feature may or may not have geometric aspects. A geometry object defines a location or region instead of a physical entity, and hence is different from a feature. The distinction between features and geometry objects in GML contrasts with models used in other geographic information systems (GIS) that make no such distinction. That is, although some other GIS define features and geometry objects interchangeably as items on a map, GML maintains them as separate entity types.

In GML, a feature can have various geometry properties that describe geometric aspects or characteristics of the feature (e.g. the feature's Point or Extent properties). GML also provides the ability for features to share a geometry property with one another by using a remote property reference on the shared geometry property. Remote properties are a general feature of GML borrowed from RDF. An xlink:href attribute on a GML geometry property means that the value of the property is the resource referenced in the link.

For example, a Building feature in a particular GML application schema might have a position given by the primitive GML geometry object type Point. However, the Building is a separate entity from the Point that defines its position. In addition, a feature may have several geometry properties (or none at all), for example an extent and a position.

Anyway, I have attached the current version of the candidate revision to the SF-GML Profile standard. There is currently an OGC adoption vote happening for this standard.

Regards

Carl Reed, PhD
CTO and Executive Director Specification Program
OGC

 

The OGC: Helping the World to Communicate Geographically

 

---------------------

 

This communication, including attachments, is for the exclusive use of addressee and may contain proprietary, confidential or privileged information. If you are not the intended recipient, any use, copying, disclosure, dissemination or distribution is strictly prohibited. If you are not the intended recipient, please notify the sender  immediately by return email and delete this communication and destroy all copies.

 

"The important thing is not to stop questioning." -- Albert Einstein
"Security is mostly a superstition. It does not exist in nature. Life is either a daring adventure or nothing." -- Helen Keller

10-100r2_Geography_Markup_Language_GML_simple_features_profile_v2.0.doc