1.3.4. GetFeatureInfo (optional Attribute)
"GetFeatureInfo is an optional operation. It is only
supported for those layers for which the attribute
queryable="1" (true) has been defined or inherited. A
client shall not issue a GetFeatureInfo request for other layers. A WMS
shall respond with a properly formatted service exception (XML) response
(code = OperationNotSupported) if it receives a GetFeatureInfo request but
does not support it.
The GetFeatureInfo operation is designed to
provide clients of a WMS with more information about features in the
pictures of maps that were returned by previous Map requests. The canonical
use case for GetFeatureInfo is that a user sees the response of a Map
request and chooses a point (I,J) on that map for which to obtain more
information. The basic operation provides the ability for a client to
specify which pixel is being asked about, which layer(s) should be
investigated, and what format the information should be returned
in." (OGC 2004)
If you want to learn more about the GetFeatureInfo
operation, have a look at the following pdf file (pages 31-33):OGC Web Map Service
Interface