Web Services for Geographic Information Systems

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3 Νοε 2013 (πριν από 4 χρόνια και 10 μέρες)

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Shengru Tu
and Mahdi Abdelguerfi
University of New Orleans
E
nterprises in the public and private
sectors have recently produced a
surge in Web services and Web
applications for geographic information
systems (GISs), making large spatial-data
archives available over the Internet.
Google Maps, Google Earth, and Micro-
soft Virtual Earth, for example, introduce
GIS services to ordinary Internet users
with astonishing aerial imagery and
responsive performance.
Logically, maps are a natural platform
on which information from different per-
spectives can converge through geograph-
ic locations. Technically, Web services
technologies have provided the necessary
standards for applications in different
domains to integrate with GIS data and
services.
1
Significant accomplishments in
GIS Web services have led to several
exemplifying map and image services that
adhere to Web services standards and
bring terabytes of geospatial data and dig-
ital maps to enterprise developers who
house no GIS data. Meanwhile, Yahoo
Maps and the Google and Microsoft ser-
vices we mentioned earlier are providing
numerous APIs, enabling light-weight
integration of digital maps and business
location information into any Web pages
and applications. This is a clear indication
that a broader wave of GIS Web services
applications is on its way. However, this
growing field is not without problems. This
special issue serves as a forum for crosstalk
about the models and technologies related
to GIS Web services.
Web Services and
the Challenges Ahead
Although the growth of geospatial data
and digital maps has given Internet appli-
cation developers a great opportunity to
integrate location information into their
services, achieving harmonious integration
is challenging. GIS services often transmit
very large volumes of data; geospatial
query processing involves extensive GIS
domain knowledge and requires intensive
computation; and GIS Web services clients
are traditionally heavy-duty, stand-alone
software tools.
2
These factors have made
GIS Web services more difficult to build
than the ordinary business transactions for
which general-purpose Web services were
originally intended.
IEEE INTERNET COMPUTING 1089-7801/06/$20.00 © 2006 IEEE Published by the IEEE Computer Society SEPTEMBER • OCTOBER 2006 13
Guest Editors’ Introduction
Web Services for Geographic
Information Systems
Web services are Web sites intended for use by
computer programs rather than human users. The
W3C has defined a general-purpose Web service
architecture based on a trio of standards — SOAP,
the Web Services Description Language (WSDL),
and Universal Description, Discovery, and Integra-
tion (UDDI) — as well as others for business
processes, security, coordination, transaction,
inspection, and so on.
3
In parallel with the devel-
opment of these general-purpose Web services, the
Open Geospatial Consortium (OGC) has success-
fully executed efforts for GIS interoperability. For
example, the OGC Web Services (OWS) initiative
has undergone multiple phases — including the
Web Map Server (WMS), Web Feature Server
(WFS), Web Coverage Server (WCS), and OGC Web
Service Architecture,
1
which support application
developers in integrating a variety of online geo-
processing and location services. Conceptually, the
OWS technology stack is a service-oriented archi-
tecture (SOA) that includes service discovery,
description, and binding layers corresponding to
UDDI, WSDL, and SOAP in the W3C architecture.
Rather than general issues, however, the OGC
intended to specify only those issues that are spe-
cific to geographic information. Currently, OGC
Web services aren’t equivalent to the W3C SOAP-
based Web services, although the OGC is attempt-
ing to integrate the Web services standards into the
OWS framework, including specifying changes to
the common OWS architecture and providing
WSDL descriptions in WMS, WFS, and WCS.
In this Issue
The articles in this issue’s theme section aim to
reflect the state-of-the-art development in GIS
Web services from different angles.
In “Designing and Building TerraService,” Tom
Barclay and his coauthors give technical insight
into TerraService technologies through a bottom-
up tour of the GIS Web service site’s design and
construction, as well as end-to-end descriptions of
two large-scale GIS projects that use TerraService.
As a pioneering GIS Web services provider, Terra-
Service provided W3C Web services interfaces for
one of the world’s largest geospatial databases.
Every developer looking to build GIS Web services
based on W3C standards can learn from this set of
proven technologies.
“A Distributed Geotechnical Information Man-
agement and Exchange Architecture,” by Roger
Zimmermann and his coauthors, presents another
case study on applying W3C Web services tech-
nologies, but to a GIS Web service site with addi-
tional complexity. The services aim to facilitate the
exchange and utilization of geotechnical informa-
tion stored in distributed heterogeneous databas-
es. To reduce query-forwarding traffic, the authors
also apply a sophisticated query-routing algorithm
supported by tree-based spatial indexing. This arti-
cle complements literature in the GIS field, which
often focuses on the OGC Web service approach.
The authors report that adopting the W3C Web ser-
vice approach makes it possible for developers to
use many high-quality (sometimes free) develop-
ment tools as well as access to large libraries of
various, preexisting Web services.
In “Evaluating Performance in Spatial Data
Infrastructures for Geoprocessing,” Marius
Scholten, Ralf Klamma, and Christian Kiehle dis-
cuss model-based analysis for a specific spatial
data infrastructure, a groundwater vulnerability
assessment service. This site is implemented with
multiple OGC WCSs, all of which accept SOAP
requests through a WCS-SOAP proxy. The authors
base their performance analysis on the stochastic
Petri net model and supplement it with empirical
measurements. They consider influential perfor-
mance parameters in their evaluation, including
caching, network speed, data granularity, and
communication mode.
Rob Lemmens and his coauthors present a
prototype framework for a semiautomatic Web
service chaining tool in “Integrating Semantic
and Syntactic Descriptions to Chain Geographic
Services.” The tool consists of two components:
a service discovery component that finds seman-
tically and syntactically matching services for a
given requirement description, and a service
composer that realizes the desired service com-
position into a workflow implementation. This
framework makes the basic assumption that all
participants share a collection of common geo-
ontology sets, which means that every service
provider must annotate every working service
using these shared ontology sets. The authors use
a high-quality academic ontology editor and a
Web Ontology Language (OWL) reasoner in ser-
vice discovery, which helps the prototype handle
complex knowledge representation.
Finally, John Sample and his coauthors’
“Enhancing the US Navy’s GIDB Portal with Web
Services” describes what one organization can do
when confronted with implementing a large
geospatial portal. The authors discuss two inter-
esting efforts that support Web services for GIS:
14 SEPTEMBER • OCTOBER 2006 www.computer.org/internet/IEEE INTERNET COMPUTING
Web Services for GIS
increasing WMS resources’ availability and medi-
ating clients’ requests and available services based
on domain-specific semantics.
Taken as a whole, these articles cover a wide
spectrum of issues that arise during Web services
development for GIS.
G
iven the rapidly increasing availability of
geospatial data and maps as well as GIS Web
APIs, most users of GIS on the Web will differ dra-
matically from traditional GIS users — rather than
domain experts, they’ll be ordinary people. We
believe that this will increase the demand for new
GIS Web services significantly, simultaneously
changing GIS requirements. People will no longer
limit their needs to data distribution, but will
demand direct location-aware services. GIS devel-
opers will face not only traditional concerns such
as scalability, reliability, security, and performance,
but also how to turn the traditional data-distribution
model into a service-delivery model that covers the
entire GIS space.
References
1.J. Lieberman, ed., OpenGIS Web Services Architecture, Open
Geospatial Consortium specification 03-025, Jan. 2003;
http://portal.opengeospatial.org/files/?artifact_id=1320.
2.C. Yang et al., “Performance-Improving Techniques in Web-
Based GIS,” Int’l J. Geographical Information Science, vol.
19, no. 3, 2005, pp. 319–342.
3.D. Booth et al., eds., “Web Services Architecture,” W3C
Working Group note, Feb. 2004; www.w3.org/TR/ws-arch/.
Shengru Tu is a professor in the computer science department
and the director of the Visual Computing Research Lab at
the University of New Orleans. His research interests
include service-oriented architectures, development of GIS
Web services, software integration, software testing, and
Petri nets. Contact him at shengru@cs.uno.edu.
Mahdi Abdelguerfi is professor and chair of the computer
science department at the University of New Orleans. His
research interests include spatial and spatio-temporal
information systems, parallel processing of geospatial
data, and geosensor networks. Contact him at mahdi@cs.
uno.edu.
IEEE INTERNET COMPUTING www.computer.org/internet/SEPTEMBER • OCTOBER 2006 15
Guest Editors’ Introduction
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