OWS-2 will address the issues of common architecture, image
handling and decision-support tools, information interoperability,
location-based services, and conformance and interoperability testing
and
evaluation.Addressing these issues represents an effort to create a
consistent
baseline of open geoprocessing services.
The Web Mapping Testbed (WMT), OGC's first
interoperability
initiative, took place in 1999, culminating in a presentation on
September 10,
1999.This initiative was a significant milestone for several reasons.
First,
it introduced an innovative "coopetition" methodology that brought
together
competing vendors and their customers to work toward common objectives.
Second,
it demonstrated truly interoperable Web Services for the first time -
several
years before service-oriented architectures became the preferred form
of
distributed computing.In addition, WMT was the catalyst for explosive
growth
in the OGC interoperability program.
The years between 1999 and 2003 were an exciting
period with
great creative energy generating innovative open technologies.In this
timeframe, OGC technologies were validated through numerous pilot
projects and
implementations.At the same time, these experiences uncovered the need
to
integrate and harmonize service specifications, as well as update
current IT
standards and principles.
Since the 1999 pioneering experiments, Web
Services have
matured greatly from an IT perspective.Today major software platform
vendors
are aligned in support of standard infrastructures and technologies for
Web
Services, and infrastructure support in the form of development tools
has
expanded considerably.
The Common
Architecture segment of OWS-2 will address the issue of bringing
specifications in line with today's IT standards.These standards,
which
include SOAP and WSDL, have matured under the sponsorship of
organizations such
as W3C, OASIS, and WS-I.The Location-Based Services segment of
OWS-2
will expand and refine these services, as well as harmonize with
services
developed in various interoperability projects.OGC Location-Based
Services
were created as a result of the OpenLS initiative in 2001 and 2002.The
Image
Handling and Decision Support Tools portion will address the issue
of
integrating image processing services with other geospatial services.
This
section will also look at how to link together intermediate processing
services
to create a specific image product.
In a previous column, Interoperability
- Why it Makes Good Business Sense for Our Industry, dated Feb 13, 2004, we explored the issue of
information or semantic interoperability by examining the problems that
arise
when we attempt to bring together GIS object models.In order to
achieve interoperability,
a common communication infrastructure (set of protocols) is necessary,
but this
is not sufficient.Standards for information structure and content must
be
developed, also.
These issues have emerged very clearly as
organizations work
toward deployment of Web
Feature Servers and Geographic Markup
Language (GML) technology.The OWS-2 Information
Interoperability segment will research this topic in the context
of GML 3,
which is a powerful XML description of geospatial data model.The fact
that GML
can represent very sophisticated object models without any model
standardization has been an obstacle for interoperability.OWS-2 will
tackle
this problem by developing GML 3 schemas for various data products.
Note the term "application schema" used in the previous paragraph.An application schema describes an explicit data model, including objects, attributes, relationships, and temporality.This data model is usually bound to a specific application, such as a schema for road maintenance.On the other hand, a profile describes a subset of the full language capabilities.For example, a profile may contain simple features geometry (no arcs or parametric curves) and other simplifying assumptions.Profiles can be useful to describe the functionality that certain software applications support; for example, their ability to parse GML.
A final portion of OWS-2 deals with Conformance and
Interoperability Testing and Evaluation, an issue that appears
simple on
the surface, but is quite complicated once you start looking at the
details.
Establishing that a software component is in conformance to an
interface
specification involves careful review of the specification and
developing test
suites.However, it is not easy to develop test suites that take into
account
sequence of operations, interface dependencies, validate interfaces
independent
of the test data set, and so forth.Even though conformance to the
specifications will not guarantee interoperability, it is important to
develop
a conformance test baseline and begin addressing ways of testing
interoperability.
In summary, OWS-2 is a significant initiative that will help
to consolidate and harmonize the work done by OGC up to this point.
Furthermore, it will bring OGC specifications in line with current IT
standards, and it will advance interoperability by beginning to address
the
fundamental issue of semantic interoperability.