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UNDERSTANDING
TECHNOLOGY
Web Services: The OGC Perspective
Chris Andrews
Ten years ago, in response to the proliferation of
competing, incompatible geospatial data and software
solutions, a group of industry leading organizations
formed the Open Geospatial Consortium, Inc., (OGC). OGC
intended to establish publicly useable standards for the
communication of geospatial information with the intended
purpose of enabling the connectivity of diverse geographic
software tools over networks. OGC began developing several
pioneering standards, sometimes following new information
technology (IT) industry standards and other times
preceding the IT industry into new territory. The OGC Web
Services (OWS) framework took shape in the late 1990s and
eventually developed as one of the most important
conceptual products of the OGC that is only now beginning
to change the shape of the GIS software market.
The term “web services” describes a critical
set of software technologies that are still developing
today and that form a foundation technology for software
interoperability. Web services, OWS included, encompass a
set of discreet software components that communicate over
the internet using standardized, publicly known protocols
and messaging languages. Web services contain the capacity
to provide information about themselves when queried by a
client application and may be invoked for complex
operations by a variety of applications without having to
exchange information about hardware or software platforms.
OWS describes a web services framework within the
context of the Internet for sharing and exploitation of
geospatial information expressed as geometries, images and
metadata. OWS compliant services can be accessed across
the internet, queried to discover their capabilities, and
invoked to retrieve maps, vector data, image data, or
geospatial metadata using standardized access protocols. A
more detailed set of specifications define specific
components of OWS, including Web Map Service (WMS), Web
Feature Service (WFS), Catalog Services—Web, and Web
Coverage Service. Implementations of these tools use the
Geography Markup Language (GML), an XML-based open
specification also developed by OGC, for
intercommunication. Standardized, formatted HTTP requests
are used to invoke these services. Taken together, the set
of OWS specifications define a set of flexible,
interoperable services that can be chained together to
perform tasks as diverse as generating a formatted map
product on an internet website to providing interactive
maps for a desktop application.
OGC standards are beginning to make an impact upon
the GIS software and data marketplace. Large and small
public organizations, such as Great Britain’s Ordnance
Survey, use OGC-compliant software to serve data and
provide maps over the Internet. Open source and commercial
software applications are beginning to challenge each
other for market share in the OGC applications space.
Ionic Software, SA, and Intergraph Corporation both market
commercial OGC-compliant software. The well supported
University of Minnesota’s MapServer project provides a
free, open source OGC implementation that offers strong
competition to the commercial variants. The Gulf of Maine
Mapping Portal (GoMMaP), developed by DM Solutions Group
Inc., presents a great example of a functionally rich, OGC-compliant
web application that provides maps to the public. The
GoMMap site implements MapServer and uses a distributed
network of WMS and WFS to allow users to interactively
view and create maps of marine data for the Gulf of Maine
region. Users who visit the site even have the opportunity
to learn how to use open source software to enable their
own services to provide data for the site.
OGC web services concepts and implementations are
still undergoing changes. Development of these tools is
being driven by the user community’s desire for greater
functionality and maximum performance. The OGC standards
respond well to these desires and it will be interesting
to see how the standards evolve as competitive market
pressures are brought upon the OGC-compliant software
industry.
Acknowlegdments
The author would like to thank Dean Gadoury of DM
Solutions Group Inc. and GoMOOS for their help with this
article. More information about GoMMaP may be found at http://www.gommap.org/gommap/index.html.
About the Author
Chris Andrews has been an advocate for
standardizing and expanding GIS technology in the past 8
years, programming and listening to customers in a variety
of environments from private industry to the Kennedy Space
Center. Chris is currently employed as a GIS Solution
Architect at Idea Integration in Denver, CO, and may be
contacted at [email protected].
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