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1 April 2005

XML is computer code. But don't worry.

The World Wide Web (WWW) and publishing documents to it and to the Internet has, as we all know, soared to the state of ubiquity. A technology that has made this easier for those who actually engage in this activity is Extensible Markup Language (XML).

XML is a computer authoring language for publishing documents through the WWW onto the Internet, and it provides a significantly greater flexibility and automation potential as compared with the other way of posting to the web, HTML.

Here's a sample of an XML document of an old George Burns and Gracie Allen routine that ended their shows for years. George would say to his wife Gracie as they were signing off, "Say good night Gracie." To which Gracie would reply, and instead of saying "Good night" she assumes the ditz role and says, "Good night, Gracie," which in those days was clever and would get a laugh.

We call this document 'old joke,' and after the exchange, there is applause from the audience.

<?xml version="1.0"?>
<oldjoke>
<burns>Say <quote>goodnight</quote>, Gracie.</burns>
<allen><quote>Goodnight, Gracie.</quote></allen>
<applause/>
</oldjoke>

A competitive advantage

What this has to do with you, the automation engineer, the control systems technician, and the grand audience of InTech magazine, is XML is fast taking over the world of data interchange.

What starts, grows, and prospers in the commercial world eventually wends its way into automation and control.

Software architect John Sever writing in February 2005 InTech avers, "The popularity of XML is driving automation system vendors to add XML as an optional format for control code import/export functionality.

"To take advantage of this technology, an automation system must be capable of basic control code import/export to an XML data structure. While not all systems fully support this functionality, vendors continue to add XML support to their systems. Much of their support provides an interface between the plant automation system and ERP, MES, or other business systems. In fact, it is difficult to find any information about utilizing XML other than for web applications or business system integration."

That is the code's importance. It enables, better than others, the interface of enterprise, business, automation, and control data. This is a critical aspect to acquiring competitive advantage.

Represent tabular data

The XML started off as a language for defining new document formats for the WWW.

XML is a text-based format that provides mechanisms for describing document structures using markup tags (words surrounded by '<' and '>').

Web developers may notice some similarity between HTML and XML since both come from the same parent.

XML has grown, and industry accepts that it is not only useful for describing new document formats for the Web, but it is also best for describing structured data.

Examples of structured data include information typically contained in spreadsheets, program configuration files, and network protocols.

XML is preferable to previous data formats because XML can easily represent both tabular data (such as relational data from a database or spreadsheets) and semi-structured data (such as a Web page or business document).

XML's extensibility manifests itself in a number of ways. First of all, unlike HTML, it does not have a fixed vocabulary. Instead, one can define vocabularies specific to particular applications or industries using XML.

Second, applications that process or consume XML formats are more resistant to changes in the structure of the XML being provided to them than applications that use other formats, as long as such changes are additive.

For instance, an application that depends on processing a <Customer> element with a customer-id attribute typically would not break if another attribute, such as last-purchase-date, added in to the <Customer> element.

Such flexibility is uncommon in other data formats and is a significant benefit of using XML.

XML has no ties to any programming language, operating system, or software vendor. In fact, it is fairly straightforward to produce or consume XML using a variety of programming languages.

Nicholas Sheble (nsheble@isa.org) edits the Control Fundamental department. Content for this critique comes from, among other sources, www.xml.com and www.microsoft.com. Read John Sever's Industrial Computing article on XML and XSLT in February 2005 InTech at www.isa.org/intech/ic/xml.