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Intergrated Client WFS
getCapabilities CapabilitiesDocument
describeFeatureType typeName XMLSchema
getFeatures Query GML
Transaction LockID, ... TransactionResponse
LockRequest Query LockResponse
Figure 16 Locking
The locking model is based the use of tokens, which are obtained for a requested duration. These lock tokens are consumed during the course of a transaction. Depending
on the method of use the Lock may be relinquished on just the features modified by the Transaction request.
While not providing facilities such as checkpoints, or conflict resolution this does represent a workable middle ground.
11.3 Issues and Tradeoffs with Web Feature Service Communication
There are several pitfalls in the current Web Feature Service specifications; areas where industry practice diverges from what one may expect from reading the specification.
11.3.1 Spatial Reference System
The Capabilities document produced by a Web Feature Service provides an SRS element associated with each FeatureType. The interpretation of this SRS tag is divided
depending on the format returned:
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47 EPSG:4326
The interpretation of this SRS is ambiguous in practice. The pragmatic solution is to interpret the ordinates in eastwardnorthward order, ignoring the specified order
in the EPSG database. This follows industry practice, and the use of EPSG codes by the early WMS
services. This is only a problem for a small percentage of the allowable codes. The approach is in conflict with the latest Web Map Server specification, and
represents a difference between practice and correctness.
URI Understood to indicate CRS information directly as specified by the European
Petroleum Standards Group.
WKT Provides the WKT representation of the information retrieved.
AUTO:42000,0,0,0 Reference to the AUTO projections maintained by the Web Map Server
specifications both AUTO, and AUTO2 are in use. The numbers used are “units”, “lat” and “long”. Please consult document the WMS 1.1.1 specification
for more information.
The best advice we were offered over the course of our integrated client work was to treat “EPSG:1234” in the historical manner. Use the new URI format wherever possible as its
meaning is clear and consistent.
11.3.2 WFS 1.0 and GML3
One of the difficulties in communicating with the WFS services available over the course of this documents construction is the lack of full WFS 1.1 services. As such GML3 data
actually a Simple Feature profile of GML3 was made available via WFS 1.0 services.
11.3.3 Construction of Default Styles
The GML3 specification provides guidance for rendering defaults that conflict with those provided by the Style Layer Descriptor specification.
Further more the detail of information required to construct a good default style is not available by way of DescribeFeatureType. Such information would need to be combined
with aggregate information about the data available for each attribute type.
As an example the construction of a simple sequential theme requires knowledge of the min and max values.
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11.3.4 Invalid Schemas and Conformance
