Designing open GIS conformant system architectures for the enterprise
OGC web services: The 'Dial-tone' of the spatial internet
The standard set of interoperability interfaces
and encodings that are presently enabling
enterprises to open-up their spatial systems, to
better exchange spatial data, and to reduce
system dependencies can collectively be called
Open GIS Consortium (OGC) Web Services (www.opengis.org). These standards, as
adopted and implemented by the OGC’s 230+ members, provide enterprises an
opportunity to expose their legacies through standard interfaces so that many new
applications can take advantage of legacies, through standard interfaces. Just as http:
and html/xml comprise the dial-tone of the internet, OGC Web Services and encodings
provide us with the dial-tone of the spatial internet.
Web services offer a method for publishing your computational capabilities in such a
way that others might dynamically find them and bind to them – enabling the easy
construction of “service chains” comprising modular, plug-and-play components. This
plug-and-play capability cannot be under-emphasized in what it offers architects of
new systems. Yet, it is arguably more important in what it can offer enterprise
architects who seek to “open-up” and leverage their legacy data and services as their
enterprise progresses. The promise of the ‘web services’ vision, as championed by
industry leaders such as IBM, Microsoft, Sun and others, is revolutionary. Its realization
within the realm of spatial data and distributed geo-processing has been led by the
Open GIS Consortium.
The sponsors and members of the OGC have been working over the past several years
to specify how various “web-mapping” functions can be implemented in an
interoperable, vendor-neutral manner through the use of web services. In consultation
and harmonization with ISO TC211, OGC must now be considered the sole source of
implementation-level web services specifications for interoperable, distributed geoprocessing.
In truth, the OGC pioneered the Web Map Service interface before “web services” became
a term of common use. At this stage, the OGC and its 230+ members have developed a
comprehensive set of interface specifications and encodings that enable powerful webbased
access to map data (Web Map Service), vector data (Web Feature Service and
Geography Mark-up Language – GML), and coverage data (Web Coverage Service). And,
OGC and its members have worked extensively on perhaps the biggest challenge faced
by those seeking to implement web services – how to describe the capabilities of a
spatial web service so that they (and the data that they host) might be published and
discovered in a Web Registry Service. Without machine-readable capabilities, the
integration of various components continues to be an arduous, “man-in-the-loop”
process.
Frome dumb maps to spatial applications
Much of the deployed base of OGC services is centered around the Web Map Service,
enabling easy, standards-based access to raster map data or portrayed vector data (for
instance, Shapefiles). This has been a huge leap forward for many enterprises, freeing
them to point applications against any WMS conformant server, without prior knowledge
of its API. Some companies have implemented middleware products with the WMS
interface (often called a ‘cascading’ Web Map Service), providing an application dynamic
access to distributed web map servers. While this has offered organizations unheard of
flexibility, they have aspired for more powerful applications offering feature-level access
and computation. In support of this business requirement, the Open GIS Consortium
membership later developed the Web Feature Service (WFS) specification.
The WFS enables sophisticated, webbased
geo-processing. A WFS
responds to requests (queries) with
‘feature collections’ encoded in GML
(Geography Mark-up Language), which
is based on the W3C’s XML
specification, enabling the exchange
of only the feature information
requested about a particular area.
Yet, due to various portrayal engines,
a user needn’t necessarily deal with
anything more complex than the userinterface
offered by basic webmapping
(WMS) applications. They
can merely navigate portrayed views of underlying feature data, as returned from
sophisticated WFS queries.
Some OGC member companies have chosen not only to implement the WFS interface
specification in their products, in order to enable feature level access to some data set.
They have also built powerful middleware products with the WFS interface that can
provide direct, simultaneous access to multiple, underlying engines such as Oracle
Spatial, ArcSDE, and more. Such OGC conformant infrastructure enables enterprises to
provide unprecedented applications over thin clients.
