Standard response parameters Response .1 Response Semantics

64 Copyright © 2010 Open Geospatial Consortium 11 GetFeature operation

11.1 Introduction

The GetFeature operation returns a selection of features from a data store. A WFS processes a GetFeature request and returns a response document to the client that contains zero or more feature instances that satisfy the query expressions specified in the request. The canonical representation of features uses GML see ISO 19136:2007, and the form of the GetFeature request is modelled after this representation of the result set. For this reason, it is necessary to have a clear understanding of how the General Feature Model see ISO 19109 is mapped into the GML representation. The reference description of GML is given by ISO 19136:2007 but the salient aspects are summarized here. In GML a feature is represented as an XML element. The name of the feature element indicates the Feature Type, conventionally given in UpperCamelCase see OGC 06-121r3:2009, 11.6.2, such as xmml:BoreHole or myns:SecondaryCollege. The content of a feature element is a set of elements that describes the feature in terms of a set of properties. Each child element of the feature element is a property. The name of the property indicates what the property means, conventionally given in lowerCamelCase see OGC 06-121r3:2009, 11.6.2, such as gml:boundedBy or xmml:collarLocation. The value of a property is given in-line by the content of the property element, or by-reference as the value of a resource identified in a link carried as an XML attribute of the property element. If the in-line form is used, then the content may be a literal a number, text, etc, or may be structured using XML elements, but no assumptions can be made about the structure of the value of a property. In some cases the value of a property of feature may be another feature, for example a myns:School feature may have a property myns:frontsOn , whose value is a myns:Road, which will itself have further properties, etc. 11.2 Request 11.2.1 Request Semantics Figure 17 describes the schema of a GetFeature request.