In computing, the Open Geospatial ConsortiumWeb Feature Service Interface Standard provides an interface allowing requests for geographical features across the web using platform-independent calls. One can think of geographical features as the "source code" behind a map, whereas the WMS interface or online tiled mapping portals like Google Maps return only an image, which end-users cannot edit or spatially analyze. The XML-based GML furnishes the default payload-encoding for transporting geographic features, but other formats like shapefiles can also serve for transport. In early 2006 the OGC members approved the OpenGIS GML Simple Features Profile. This profile is designed both to increase interoperability between WFS servers and to improve the ease of implementation of the WFS standard. The OGC membership defined and maintains the WFS specification. Numerous commercial and open-source implementations of the WFS interface standard exist, including the open-source reference implementations GeoServer and deegree. The OGC Implementing Products page provides a comprehensive list of WFS implementations.
Overview
The WFS specification defines interfaces for describing data manipulation operations of geographic features. Data manipulation operations include the ability to:
get or query features based on spatial and non-spatial constraints
create a new feature instance
delete a feature instance
update a feature instance
The basic Web Feature Service allows querying and retrieval of features. A transactional Web Feature Service allows creation, deletion, and updating of features. A WFS describes discovery, query, or data transformation operations. The client generates the request and posts it to a webfeature server using HTTP. The web feature server then executes the request. The WFS specification uses HTTP as the distributed computing platform, although this is not a hard requirement. There are two encodings defined for WFS operations:
In the taxonomy of Web Services, WFS is best categorized as a non-RESTful RPC type service.
Communication models
The WFS Web Feature Services or Web Feature Server specification supports two communication models:
Stateless Request Reply
Pub/Sub
The WebNotification Service is one of the implementation specifications for the Pub/Sub model. Regardless of the model, URL format is used and specified in the WFS specification. At this time there are no open-standard implementations of WNSs. Vendors plan to release implementations once the standard has been ratified.
Data
Data passed between a Web Feature Server and a client is encoded with Geography Markup Language, an XML dialect which can be used to model geographic features. The 1.0.0 version of the WFS specification requires the use of GML version 2.1.2, while the 1.1.0 version of the WFS specification requires the use of GML version 3.1.1. For both versions of the WFS specification, an arbitrary number of other encodings can also be defined, in addition to the required GML 2.1.2 or 3.1.1 format. GML 2.1.2 contains encoding support for basic geometric 'primitives': points, lines, polygons, etc. GML 3.1.1 contains encoding support for more advanced geometric representations: curves, surfaces, multi-dimensions. In addition, GML 3.1.1 includes encoding support for topologically integrated datasets.
Public Interfaces
Static Interfaces
The static interface model for the OGC Web Service model appears in the figure below. The Transaction and LockFeature operations are also optional. When writing a WFS, you must implement the following operations:
GetCapabilities - this queries the WFS service to determine available options.
DescribeFeatureType - this retrieves the XML schema to allow the WFS client to parse the resultsets.
GetFeature - this performs the actual query - parameters such as bounding box and any other filters should be passed in, as appropriate, and the WFS service then returns a GML resultset containing full geometry and feature attributes.
Dynamic interface updates
The client gets updates by one of two mechanisms:
Notification: Recommended but not mandatory. Depends on the availability of a WMS implementation.
Polling: Use this method if a WMS implementation is not available.
WFS dynamic interface web notification model This model uses the OGC Web Notification Service to send update notifications to registered clients.
