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WEB SERVICE BASED WEB FEATURE SERVICE
Wenjue Jia, Yumin Chen, Jianya Gong, Aixia Li
State Key Laboratory for Information Engineering in Surveying, Mapping and Re«»ote Sensing, Wuhan University, 129
Luoyu Road, Wuhan, HuBei, China, 430079 ^7
Commission VI, WG VI/2
KEY WORDS: Web Feature Service, Web Service, Spatial data sharing and interoperability
ABSTRACT:
The spatial information interoperability method based on web (xml) standards is the best method to implement spatial information
sharing and interoperability through the Internet at present time. Web Feature Service (WES) is a geographic information service
implementation specification based on XML provided by OGC and ISO/TC211. This paper give out the implementation method and
key techniques of WFS using Web Service technique, and give out an application sample in the end.
1. INTRODUCTION
With the development of spatial information application and the
network technique, the spatial data between different districts
and different departments need to be shared and to be
interoperated. ISO/TC211 and OGC have done lots of work to
define Interface specifications and standards to ensure sharing
and interoperable capability of the spatial data. Compare with
the CORBA, DCOM and SQL interface specifications defined
by OGC, the implementation specifications defined on web
(XML) are more successful for they using open standards and
protocols, and having the capability of cross-platform and
cross-firewall. The emergence of Web Service technique
overcomes the shortcoming of traditional Distributed Object
technique and provides the interoperable capability of
cross-platform and cross-language in distributed net
environment . Web Feature Service is one of the GIS web service
interoperable specifications defined by OGC. It’s the most
powerful data service of OGC web service. It can get data and
even can update, delete and create data. OGC has defined the
Interface of WFS using XML, and appointed HTTP as the
distributed computing platform. This paper give out the
implementation method and key techniques of WFS using Web
Service technique, and give out an application sample at the end.
Chapter two briefly introduces Web Feature Service
Implementation Specification and Web Service technique,
chapter three gives out the architecture design of WFS based on
web service technique, chapter four gives out a implementation
method of WFS, chapter five discusses GML application schema
definition used for WFS, chapter six introduce the WFS client
and chapter seven gives out a WFS application example. The last
chapter is conclusion.
2. WEB FEATURE SERVICE AND WEB SERVICE
TECHNIQUE
Web Feature Service is a geospatial data manipulate interface
based on HTTP protocol provided by OGC. It belongs to Data
Service according to OGC web service architecture and it is the
development of OGC Web Map Service. Web Feature Service
allows a client to retrieve geospatial data encoded in Geography
Markup Language (GML) from multiple Web Feature Service.
And it supports INSERT, UPDATE, DELETE, QUERY and
DISCOVERY operations on geographic features using HTTP as
the distributed computing platform. WFS defined 5 operations:
GetCapabilities operation describes capabilities of the web
feature service using XML, it indicate which feature types it can
service and what operations are supported on each feature type.
DescribeFeatureType operation describes the structure of any
feature type it can service. GetFeature operation services a
request to retrieve feature instances. In addition, the client
163
should be able to specify which feature properties to fetch and
should be able to constrain the query spatially and non-spatially.
Transaction operation services transaction request, it can create,
update, and delete operations on geographic features.
LockFeature operation processes a lock request on one or more
instances of a feature type for the duration of a transaction
The working process of a web feature service is as following:
first user request GetCapabilities, this operation return a
capabilities XML document including geospatial data
information which can be provided by the service. Then user
send DescribeFeatureType request for the interesting data
according the response of GetCapabilities operation. The
response of DescribeFeatureType returns the GML schema of
selected geospatial feature type, using this information, user can
understand well with the returned GML data. Next user can send
GetFeature or Transaction or LockFeature operation to query or
manipulate geospatial data.
Web Feature service has two functions. First, it can implement
geospatial data web service, data provider can establish a web
feature service upon on spatial database to provide online data
service. Second, it can implement interoperate between
heterogeneous system. Two different GIS software can realize
heterogeneous data interoperability, including query, browse,
update etc.
According to OGC Web Feature Service implementation
specification, a web feature service uses HTTP protocol to send
request and get response. It not appoint to a specific implement
technique, so people can use different technique to implement a
web feature service such as CGI, ASP, JSP, PHP etc. Using CGI
technique, when a web feature server receives a request, it must
generate a new process to service user request, when lots of user
requests come at nearly the same time, it will cost lots of server
resource so the service performance becomming poor. ASP, JSP
and PHP are server page technique, they can make separation of
page logic and process logic, the server generates Thread not
Process to service user request, so it can promote performance
effectively. These techniques mainly for user-machine interface,
they can provide friendly user interface using web pages, but
web pages not fit for services integration and interoperability.
The emergency of Web Service technique provides a new and
effective means to integrate and to interoperate. Web Service is a
kind of self-contain, self-describe software Component can be
discovered and to be invoked by other software Component.
Web feature service provider can use any programming
language at any platform to implement web feature application,
and then publish it as a web service. The implementation detail
is black box for users, so service providers do no need to worry
