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OGC Approves Major Specifications for GeoSpatial Web Services 10.04.2002

October 4, 2002
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The Open GIS Consortium Inc. (OGC) announced that three new OpenGIS Specifications were approved at the recent meeting in Noordwijk, The Netherlands. The Web Feature Service Interface Specification (WFS), the Filter Encoding Implementation Specification and the Style Layer Descriptor (SLD) Implementation Specification are significant contributions to the Spatial Web - moving the global community closer to the OGC vision of ubiquitous geospatial integration on the Web, regardless of hardware platform, device or software. The specifications are freely available at

Each specification solves significant interoperability issues for mapping data and service integration on the Web. Vendor products that implement the Web Feature Service Specification can support distributed, Web-based geospatial feature data operations critical to government, commercial, academic and other applications. In particular, software that implements WFS can access, query, create, update or delete data from servers that adhere to the specification, no matter the vendor, data storage format or location. For example, for a given situation there are no roadblocks to updating, sharing and using mapping information at the most detailed level. The Filter Encoding Specification enables any client to specify a query for information from WFS enabled server. The Style Layer Descriptor Implementation Specification provides the ability to describe rules for symbolizing maps.

The Web Feature Service Implementation Specification describes feature database operations (e.g., points, lines, and polygons) making it possible for client and server applications to interoperate across the web. The request is typically generated on the client and posted to a WFS server. The WFS server reads and executes the request, returning the result in Geography Markup Language (GML) encoding. The GML document, used in conjunction with an XML Schema, can then be parsed by any client application for further use.

The Filter Encoding Implementation Specification adds the capability to constrain feature requests to a WFS enabled server by using a filter expression within a request. A filter expression described in XML can, for example, limit selection to just those features that lie within a geographic area, or include a spatial operation (trees must be within 20 feet of an electric line) with a property constraint (must be a maple tree). The neutral XML filter encoding allows easy parsing and validation by a WFS server before being transformed into the targeted language of a required data store.

The Style Layer Descriptor Implementation Specification defines the encoding for symbology, styling and rules for map display. SLD, expressed in an XML document, can be used or referenced by a Web mapping client application when formulating a map request to any SLD enabled map server. Using this approach, Web maps can be generated dynamically using a number of independent map services accessing a number of remote data sources. Performance and efficiency is achieved since only the resulting maps need to be transported to the client as opposed to the data itself.

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