Database Server Models for WMS and WFS Geographic Web Services - Geographical Information Systems: Trends and Technologies - page 145

proposition for a Web service. In the third part, we present a user-oriented
database schema transformation. We end this section with a synthesis of
such propositions.

OGC propositions

Among the propositions defi ned by the OGC, we focus on specifi c operations
associated with Web Services: the Web Map Service (WMS) and the Web
Feature Service (WFS). We particularly focus on the GetFeatureInfo and
GetFeature operations available in these services.

WMS

Information provided in this part is based on the standard documentation
for WMS version 1.3.0 (OGC 2006). The WMS standard induces three
main operations: GetCapabilities, GetMap, and GetFeatureInfo. Figure
1 shows these operations. First of all, we present relevant operations for
our topic: GetMap and GetFeatureInfo. Then we present the limits of the
GetFeatureInfo operation.
The most important facility for a cartographical server is to provide
a map from its available layers. Parameters such as desired layers,
representation styles, size, relevant geographical areas, the projection
system or the output format must be provided to the GetMap operation.
The obtained result is a map (in general an image that can be displayed by
conventional web browsers). This operation corresponds to a visualization
process.
The GetFeatureInfo operation corresponds to a query process. This
is a mandatory facility for a Webmapping application. Webmapping is a
word used to represent cartography on the web. Within this generic word
different applications are grouped covering a wide range spectrum from

WMS Client

GetMap GetFeatureInfo

GetCapabilities

XML XML

WMS Server

Fig. 1. WMS GetCapabilities, GetMap and GetFeature operations.