1 June 2002
Exchanging Data with XML—Part I
This hot new Web language sounds great, but really—what is it?
By Al Chisholm and Charlie Gifford
Everyone seems to be talking about XML, the hot new Web language. It's supposed to hold tremendous promise for process control and automation, facilitate a profound paradigm shift, and deliver structured data to the desktop for computation and presentation. That sounds great, but really—what is XML?
What Language Is This?
Put simply, XML, or extensible markup language, is the universal language for data on the Web. It gives developers the power to deliver structured data from a wide and ever-increasing range of applications to the desktop and makes server-to-server transfer of structured data possible.
Because XML provides a uniform method for describing and exchanging data, it also has the potential to fully leverage the wealth of information on Internet protocol (IP) networks around the world. With the explosive growth of IP networks for almost every kind of business communications, XML is gaining an increasing share of the technological spotlight as a powerful tool. And by simplifying the exchange and application of data across the Web, the language allows for new data manipulation and viewing applications. Suffice it to say that developers are intrigued by the possibilities the versatile new language offers.
What Can It Do?
Originally, XML was a subset of the standard generalized markup language (SGML) that was optimized for delivery over the Web. The World Wide Web Consortium defined XML as a vendor-neutral industry standard, ensuring that structured data would be uniform and independent of applications.
As a meta-markup language that provides a format for describing data, XML facilitates exposition of content and search results across multiple platforms, with more meaning and greater precision than any other Web-enabled language offers. Its extensibility, structural representation of data, and ability to separate data from the presentation and process are key elements of its powerful functionality.
In recent years, hypertext markup language (HTML), hypertext transfer protocol (HTTP), and IP have revolutionized the way information is distributed, displayed, and searched for. Organizations rapidly embraced browsers and search engines with the creation of corporate intranets, then extended these to customers, suppliers, and business partners in the form of extranets. XML is seen as a resource that can help developers and users take full advantage of the Internet's capabilities.
Complementing HTML, XML's ability to describe structured data in an open text–based format and deliver this data using standard HTTP is important for two reasons: First, XML will facilitate more precise declarations of content and more meaningful search results across multiple platforms. Second, once the data is located, it will allow a new generation of data viewing and manipulating.
I Need More Details . . .
In XML, an unlimited set of tags may be defined. While HTML tags can display a word in boldface or italic, XML provides a framework for tagging structured data. Users can take an XML document and insert new information into it without interfering with existing content or someone's ability to parse the document.
As XML tags are adopted, there is a corresponding capability to search for and manipulate data, regardless of the application in which the data resides. Once located, data can be delivered over the network and presented in a standard browser in any number of ways, or be handed off to other applications for further processing and viewing. In this way, XML extends naturally.
XML's structural representation of data has proved broadly applicable and simple to deploy. The quality and strength of this tree-structured data format has been shown to be reliable and robust in thousands of industrial implementations of SGML.
Also, XML lets data on a client desktop be manipulated, edited, and presented in multiple views without refreshing the browser. Therefore, servers are much more scalable because of low bandwidth loads and computation requirements. Also, because data is exchanged in XML, it is easily merged from disparate sources.
The language is particularly valuable to Internet- and intranet-based applications, as it provides interoperability via its flexible, open standards–based format, plus its new ways of accessing legacy databases and delivering information to Web clients. XML allows applications to be built without custom code and easily maintained, all while providing multiple views of the data.
Where Can You Use It?
The power and elegance of this language are largely derived from its ability to maintain separation of the user interface and structured data. By separating process and presentation, XML allows for the seamless integration of data from multiple and diverse sources. Information can be converted from XML on the middle tier of the typical three-tier architecture, allowing data to be exchanged online. Encoded XML data is then delivered to the desktop, with no need to write interfaces for legacy data stored in mainframe databases or documents. Because HTTP delivers XML over the network, no changes are necessary for this functionality.
Also, whereas HTML specifies how to display data within a browser, XML defines data count. For example, in HTML, users tell a browser to display data as boldface, standard, or italic. Meanwhile, in XML, tags describe the data (e.g., name, address, city, state, ZIP code). XML separates the data from the presentation and process, enabling users to display and process the data by applying different style sheets and applications.
When used with HTML, XML offers fast delivery of data for desktop computation, the necessary view of structured data, the integration of data into common logical views, the description of data from widely varying applications, and better performance through granular updates.
With all the functions and strengths listed above, XML's uses are seemingly limitless. For example, at the enterprise level, XML can connect dissimilar systems and implement business-to-business relationships. On the factory floor, XML can translate bus languages, using a common language even when the devices are dramatically different. Customers in a variety of applications have to be jumping at the possibilities XML offers.
Where Is XML Headed?
The future is now with XML. Industrial and corporate standards are under development, and with the formation of the OPC/XML Working Group announced at ISA TECH/1999, XML will be the data-transfer medium of the future. Most manufacturing execution system and supply-chain software vendors are planning an XML version for the last half of 2000. Consequently, this protocol will be the major tool for integrating the plant floor with the enterprise.
The profound emergence of the Internet has caused a monumental shift in the way companies do business—without the benefit of tools designed to optimize its performance. The rise of XML as a dominant Web language indicates that tools are catching up with the infrastructure they service.
By enabling faster application development, better and easier system maintenance, and customer-specific data visibility, XML gives developers the power of flexibility and adaptability. In the future, as business and industrial markets increasingly depend on the Web, customers will find that XML is a tool they'll be able to use to great benefit—and that's speaking their language. IC
About the Author
Al Chisholm has more than 25 years of experience in creating factory automation and process control software. As chief technical officer and co-founder of Intellution Inc., he also serves as technical director and is a member of the board of directors of the OPC Foundation. Chisolm is a graduate of Brown University and holds an M.S. in computer and information science from the University of Massachusetts. He has written numerous articles for trade publications and conferences and gives frequent lectures on OPC and related topics all over the world.
Charlie Gifford is an industrial IT specialist with more than 14 years of experience in facility and system analysis and design. Currently, he is a manager for the Interprise Supply Chain Solutions Group at AnswerThink Consulting Group (Miami). His group directly manufactures in an e-business environment by connecting the customer, suppliers, corporate, and the plant floor through MES, ASP, flow manufacturing, warehouse/distribution management, and global supply chain partnering. Gifford received two B.A.s in chemical and material engineering and an M.S. in electronic materials processing from the University of Maryland.