XML - Gateway to interoperability
DOM is used to provide users with a common interface to access and manipulate the structure
and content of HTML and XML documents. It allows the application program to traverse XML
nodes, and access the structure of the XML document. DOM can be extended using related
technologies to access embedded attributes and update those attributes. Any two DOM
implementations accessing the same document will, by definition, create the same structural
model of that document. This concept is called structural isomorphism (W3C, 2000), and it is a
key reason that DOM lends itself so well to application in a standardized data interoperability
framework.
XSLT
XSL Transformations (XSLT) is a W3C working draft that defines the syntax and semantics of
XSLT, which is a language for transforming XML documents into other XML documents (W3C,
2002).
The function of XSLT is to allow for a structured, rules-based method for transforming one
XML document into another. XSLT is a unique application of XML, in that it can be considered
a true programming, or scripting, language (Harold and Means, 2002). XSLT allows the
application programmer infinite control over parsing and transforming any XML document. The
primary application of XSLT to the GIT industry lies primarily in its ability affect rapid and
repeatable transformations (migrations or conversions) of data between different end-user GIS
platforms or ancillary applications. This could include creating a real-time, or near real-time,
interoperability framework, or simply providing an import path into the end-user system.
Industry Standards
The GIT industry has undertaken several initiatives to utilize XML and related technologies to
establish standards for the structured exchange of spatial data. Those standards include, among
others, MultiSpeak, GML, and LandXML.
MultiSpeak?
MultiSpeak is an interoperability framework conceived and developed by the Cooperative
Research Network (CRN) of the National Rural Electric Cooperative Association (NRECA) in
collaboration with utility industry software vendors and consultants. MultiSpeak is an XML
DTD that defines a standard format for passing information between MultiSpeak compliant
software packages. The goal of MultiSpeak is to ease the task of application integration for small
to medium sized utilities. The MultiSpeak model is specific to electric utility implementations.
GML
The Geography Markup Language (GML) is an XML encoding for the transport and storage of
geographic information, including both the spatial and non-spatial properties of geographic
features (OGC, 2001).
The OGC conceived GML as a standard that would provide the following benefits:
- Provide an open, vendor-neutral framework for the definition of geospatial application
schemas and objects;
- Enable the creation and maintenance of linked geographic application schemas and
datasets;
- Support the storage and transport of application schemas and data sets;
- Increase the ability of organizations to share geographic application schemas and the
information they describe.
GML is a much more robust application of XML as a data format. It utilizes XML Schema to
define custom data types and define relationships, and it is not specific to any industry, but rather
provides a standard framework for the storage and exchange of any spatial information.
LandXML
The LandXML schema facilitates the exchange of data created during the Land Planning, Civil
Engineering and Land Survey process (LandXML.org, 2002). LandXML is an XML application
that utilizes XML Schema to define relationships and custom data types. Much like GML,
LandXML is a fairly robust application of XML as a data format. However, it is targeted
specifically towards land planning, engineering and survey applications.
GIT Applications
Application Interoperability
XML has gone from relative obscurity to almost universal acceptance as a data interchange
format in the matter of a few years. Data-intensive Internet exchanges and enterprise application
integration (EAI) implementations are now dominated by XML-based data formats. The
structured, standardized nature of DOM and XML, the structural isomorphism mentioned in the
technology standards discussion, allows for cross-platform implementations of applications that
streamline the transport, presentation and management of data.
GIT implementations will benefit from the advances made in the EAI industry with regard to
XML as a data format. GIS will now be able to share data with OMS, Work Management
Systems (WMS), and Customer Information Systems (CIS) in near real-time or real-time
fashion. This will enable the elimination of redundant processes, thereby leveraging and
extending key business process investments. XML applications such as XML Schema can be
integrated into the EAI framework to ensure that specialized business rules are enforced.
Finally, initiatives like MultiSpeak? will make this work easier and more cost-effective for
smaller entities by defining the target EAI framework up front and allowing software vendors
and system integrators to build to that specification.
Field Force Automation
Field force automation is of particular interest to companies with significant outside plant assets.
Utility companies have long recognized the benefits of making geospatial information available
to their employees and sub-contractors. As technological advances in communications and
computing make wireless information exchange faster and cheaper, companies will realize the
benefits of XML data formats and applications that enable IT departments to present large
quantities of graphic and non-graphic information to field crews, inspectors, and construction
sub-contractors.
Originally, digital data products distributed on CDs or specialized data-push applications
designed for use on Innovative Technologies data terminals have dominated the Innovative Technologies mapping and field force
automation market. These first and second-generation applications are slowly giving way to the
third-generation of Innovative Technologies mapping and field force automation products based upon XML
technologies.
Because XML is text-based, it responds favorably to traditional compression methods. This
allows the transport of large volumes of compressed XML data via the wireless Internet in a near
real-time data-pull or real-time synchronized manner. Telephones, hand-held computers, and
TabletPCs will soon replace Innovative Technologies data terminals and laptop computers as the necessary
hardware for these applications, further reducing the cost and complexity of Innovative Technologies computing
implementations.
Legacy Data Migration
As more spatial data interchange formats built upon XML technologies become available, XML
applications like XML Schema and XSLT will make migration between end-user GIS systems
faster and easier. Schema-based formats like GML and LandXML are already in use as standard
interchange formats for several end-user applications. Other open systems utilize GML as their
standard data storage format. As GIS applications begin to support imports of XML data,
migration into and out of those systems will become an off-the-shelf document transformation
process.
XML Schema will allow the validation of source and target datasets against their respective
schemas, and XSLT will present framework for creating rapidly deployable and repeatable
migrations processes using standard XML interchange formats.
Conclusion
XML and related technologies play a key role in facilitating application and data interoperability.
In addition, new growth areas like field force automation and legacy data migration will benefit
from the application of XML-based technologies that leverage existing investments in data and
processes. The open, extensible structure of XML coupled with technologies like DOM and
XML applications like XSLT and XML Schema makes XML a good choice for the development
of standardized data interoperability frameworks. Industry initiatives like MultiSpeak, GML and
LandXML bear out this point and illustrate how spatial data can be modeled, managed, and
exchanged using this technology.
Lately, the trend in the GIT industry has been towards more open standards of information
storage and interchange. XML will continue to expand this trend and provide application
programmers a standardized framework for the development of rapidly deployable applications
and scalable integrated GIT implementations.
References
Harold, E. R. and Means, W. S., 2002. “XML in a Nutshell”, 2nd Edition, O’Reilly and
Associates, Inc.
LandXML.org Industry Consortium, “LandXML Schema Version 1.0 Reference”,
LandXML.org, 7 June 2002, < http://www.landxml.org/spec.htm> (1 November 2002).
Specification.
McNaughton, G. A. and Martin, G. E., 2001, “Common Interfaces for Enterprise Integration –
Experience With NRECA’s MultiSpeak? Specification”, 2001 IEEE Rural Electric Power
Conference Proceedings.
OpenGIS Consortium, "Geography Markup Language (GML) 2.0", OpenGIS ? Consortium, 20
February 2001,
http://opengis.net/gml/01-029/GML2.html (23 October 2002), Abstract.
World Wide Web Consortium, “Document Object Model (DOM) Level 2 Core Specification”,
The World Wide Web Consortium, 13 November 2000,
http://www.w3.org/TR/DOM-Level-2-
Core/ (1 November 2002), Abstract.
World Wide Web Consortium, “Extensible Markup Language (XML) 1.0, Second Edition”, The
World Wide Web Consortium, 6 October 2000,
http://www.w3.org/TR/REC-xml (11
September 2002), Abstract.
World Wide Web Consortium, "XML Schema Part 0: Primer", The World Wide Web
Consortium, 2 May 2001,
http://www.w3.org/TR/xmlschema-0/ (1 November 2002),
Abstract.
World Wide Web Consortium, "XSL Transformations (XSLT) Version 2.0", The World Wide
Web Consortium, 16 August 2002,
http://www.w3.org/TR/xslt20/ (11 September 2002),
