Issue link: https://read.dmtmag.com/i/27856
The Global Use of GML Application Schemas OPENGEOSPATIAL CONNECTION T BY HERVÉ CAUMONT he Open Geospatial Consortium (OGC) Geography Markup Language (GML) Encod- ing Standard provides a basis for defining, documenting and encoding information-community or domain “application schemas” that enable data interoperability by leveraging the knowledge and consensus embodied in independently developed applications. Communities seeking to improve intra- and inter-community data interoper- ability benefit from OGC’s unique offering of structure, process, standards expertise and outreach support. Community development of GML application schemas—together with relevant UML models, registries and technical guidelines—provides better understanding of domain requirements, better interoperability and supports the harmonization of communi- ties’ spatial datasets and services. 2010 has seen considerable GML AND GEORGE PERCIVALL application schema development activ- ity: 32 GML application schemas have been posted at the OGC Network (www. ogcnetwork.net/node/210), and many others are under development. Several OGC Technical Committee Domain Working Groups have formed primarily to develop GML application schemas. Hervé Caumont is the ERDAS repre- sentative within the OGC Interoperability Program Team; e-mail: Herve.Caumont@ erdas.com. George Percivall is the chief architect with OGC; e-mail: gpercivall@ opengeospatial.org. 32 International Acceptance Across the European Union Member States (through the INSPIRE Directive) and in the United States, GML appli- cation schemas are becoming the mandated or de facto means of sharing environmental spatial information. The international GEOSS initiative, conducted by the Group on Earth Observations, includes an ongoing Architecture Implementation Pilot that provides contributed components and services through interoperability arrangements in support of societal-benefit areas. The GEOSS Standards Registry (seabass.ieee.org/groups/geoss) includes GML application schemas that are recognized among national and international contributing agencies such as GeoSciML (for Earth sciences), Observations & Measurements, and others. G E O W O R L D / M A R C H 2 O 1 1 What’s Involved? Defining and agreeing on the details of domain features, such as “interstate highway” in a roads model, is the basic task to perform when encoding business objects in GML. Application schema devel- opers don’t have to master the entire GML stan- dard—a comprehensive and complex system—but rather trimmed-down GML profiles. Identifying domain features relies on the General Feature Model of ISO19109:2005, “Rules for Application Schema,” which involves defining a feature as a representation of a real-world object or phenome- non and its relevant properties. Such properties include feature attributes (position, geometry), associations (hierarchy) and operations (dynamic changes of the feature over some range, such as time). Work remains to develop fully operational application schemas that provide elaborated associations and operations. Many initiatives also refer to a Feature Catalogue from ISO19110, “Methodology for Feature Cataloguing,” which defines and binds the features and properties of an application schema. OGC and ISO work closely together, ensuring that their standards work well together. More semantic interoperability is needed to help communities overcome their different ways of naming things to share data, and the need for harmoniza- tion tools and methodology occurs at technical and governance levels. Semantic Web technologies (that enable the Web to “understand” and satisfy requests) and the Open Linked Data concept (a method of exposing, sharing and connecting data via URLs on the Web) are ways to achieve this vision with more automated processes. Technically, the harmonization of the data dictionaries requires the ability to analyze and cross- match existing naming schemas. Organizationally, harmonization is a multi-stakeholder process, where each contributed schema must be kept “as is” to the extent possible, while integrated to the degree necessary for joint operations. Such a process involves the governance of online registries for publication, maintenance, and exploita- tion of data and service assets across organizational boundaries. Associations in industries and scientific disciplines, and data councils in regions of cooperat- ing governments, can assume responsibility for this work. OGC provides such organizations with structure, process, standards expertise and outreach support. The breadth of work already accomplished in the area of GML application schemas is staggering, and this effort has been done for the simultaneous benefit of specific and more-general geospatial communities. And all this information can be freely downloaded from the OGC Web site.