Standards Profiles - Making Standards More Interoperable and Less Complex
The GML Simple Feature Profile (GML SF) specification defines a set of encoding rules that allow only simple feature geometries to be encoded: points, lines, polygons and a few others. This subset is particularly useful for applications that intend to use the Web Feature Service Implementation Specification to define an interface for sharing and editing vector data, since it can operate effectively with just a small set of geometry types.
Consider the implications of this profile to software developers. A vendor who wants to implement support for GML in its software, can choose to support the full (600 page specification) or just the Simple Features Profile (30 pages). The latter means that programmers need only to insure the ability to write out and read that small subset of possible feature types defined in GML SF. When the GML specification was first approved, some software vendors were wary of implementing it due to its size and complexity. They believed that the cost to develop and support GML might not be worth the effort. With the approval of the Simple Features Profile more and more vendors are implementing this smaller subset of GML. That in turn will mean more wide ranging interoperability for software integrators and end users.
GML in JPEG 2000 for Geographic Imagery Encoding Specification
The GML in JPEG 2000 Profile (
http:// www.opengeospatial.org/standards/gmljp2) is geared to a specific task: to provide only the information relative to an image, including that which is needed to locate the image on earth's surface. The profile works in part because ISO, under whose auspices the JPEG 2000 Specification was developed, left a "box" available just for the storage of that information. As with the Point Profile, this is a tiny, trimmed down GML profile; the entire specification would be far too much.
GML Profile for GeoRSS
RSS (Really Simple Syndication or Rich Site Summary) is a tool to Web feed information via XML. The GML profile for GeoRSS (
http://www.georss.org/gml. html) defines a specific structure to store spatial information in those XML documents. In fact, GeoRSS GML is a super-set of the GML Point Profile and a subset of GML Simple Features Profile. It includes just four geometry types: point, line, polygon and box. GeoRSS was developed by a consensus collaboration of a number of interested geospatial and IT professionals and is not currently an approved OGC specification.
Creating Profiles
Profiles can be defined and used without going through an OGC approval process. Since many of the GML profiles to date have come from inside OGC, they have also been submitted for formal OGC approval. Those that are approved store their details in the official namespace, a webpage permanently assigned to that specification. For GML, the namespace is
http://www.opengis.net/gml.
Build Your Own Profile
As part of its work on GML, OGC has developed a tool that anyone can use to build a GML profile. The profiling tool (a pair of XSLT scripts) is actually part of
the GML 3 specification and permits the automatic generation of a profile, or a profile starting point, should users want additional manual editing or schema restriction.
The Future
The handful of OGC approved GML profiles are likely to be just the beginning of a long list. The GML Simple Features Profile has already persuaded software vendors to implement support for GML, where they chose not to be in the past. The GML in JPEG2000 Profile offers a simple way to store imagery-related data inside the ISO JPEG2000 format. Other GML profiles, some formally approved by OGC and others that are not, will appear in the coming months and years, which offer ways to create the subset of the complex whole for the job at hand and thus making everyone's geospatial data encoding and sharing more interoperable, and less complex.