OGC Launches OWS-2

By Dr. Ignacio Guerrero

OWS-2_Guerrero Recently, the Open GIS Consortium (OGC) announced the launch of a major new initiative, Open Web Services Part 2, or in short, OWS-2.For details, refer to the OGC press release dated March 19, 2004. Since its inception, OGC has been advancing geospatial interoperability as part of a vision to bring GIS into the IT mainstream.OWS-2 is an important step in this direction.

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.

Published Saturday, May 8th, 2004

Written by Dr. Ignacio Guerrero

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