Web Feature Service

Under a WFS, English Web Feature Service refers to the Internet-based access to spatial data within a distributed GIS. The WFS it is limited exclusively to vector data, as they can be stored in databases.

As part of the specifications of the Open Geospatial Consortium ( OGC), a WFS provides access to geographic features in databases and returns the result as a least -independent file format Geography Markup Language (GML ).

Under a feature is understood to be the general abstraction of a real Faktums ( "real world phenomenon" ). A feature model is a representation of using a name other attributes and, at geographical feature types, with a geometry. For example, a database feature type of the " river ". An instance of a feature ( a feature instance ) is so then a concrete river.

Technical background of an OGC - compliant WFS

To an OGC - compliant WFS - that is, a Web Feature Service, the specification of the Open Geospatial Consortium ( OGC) fulfilled - to use is resorted to date of communication by the Hypertext Transfer Protocol (HTTP). The request is sent there as a HTTP request from a client to the WFS. The WFS has six operations that can be requested by a user:

Taking these operations as a basis, one can distinguish three types of WFS:

This must be a mandatory WFS requests with the first three operations offer the Transaction Request and LockFeature are optional. The latter must not be implemented in a WFS with write access.

Therefore, the usual flow of communication between the client and a WFS in a distributed system is as follows:

• The client queries the GetCapabilties request according to the capabilities of the WFS and the offered FeatureTypes.
• Building on that, be viewed with the DescribeFeatureType Request the structure of each feature type.
• This can be requested with the GetFeature Request a special instance of a feature. Alternatively, can be performed with write access to the Transaction or the LockFeature Request for a WFS.

Within the OGC context the connection of a Web Feature Service with a Web Map Service (WMS ) is an example of the architecture of a distributed GIS. The WFS is responsible for the access to geospatial data, while the WMS is responsible only for the visualization of the data. Here, the WFS limited to the access of vector data, while another service, the Web Coverage Service ( WCS) controls the special access to raster data.

Thus, within the meaning of client-server principle is the WMS client of the WFS. In addition, this WFS as cascading WFS client again be one or more additional WFS. This architecture can be seen as a type of Web GIS.