Sharing, Drilling Down via XML and its Relatives

Snowed under by volumes of ever-multiplying Web-posted information? It’s challenging enough just to regularly find and grab data helpful data.

It also can be testy to keep information updated or exchanged accurately with others. Fortunately, three ubiquitous indispensable e-communication tools help ease frustrations and simplify information gathering and distribution: eXtensible markup language (XML) and two of its relatives, simple object access protocol (SOAP) and really simple syndication (RSS).
 

As the World Wide Web Consortium (W3C, www.w3c.org) emphasizes in its XML tutorial (www.w3schools.com/xml/xml_whatis.asp), XML “was created to structure, store and to send information.” It describes data. It does not replace hypertext markup language (HTML), which Web browsers use to display data and graphics.  

XML is a derivative of the International Organization for Standardization’s Standard Generalized Markup Language, or SGML. That’s a meta-language—a language used to make statements about object languages—in which end-users can define tags for documents. That ability to define differentiates HTML from XML. The hypertext language predefines format tags or labels such as to describe the entire document, or to identify the document’s content. But with the extensible language, end-users define the tags.  

XML allows those users to not only exchange data between mismatched systems and store data, but even to embed it in HTML documents. This is important because it allows users to focus on data format and display in HTML, not modifications when data change.  

A lightweight XML-based messaging protocol that forms the foundation of a Web Services stack, SOAP facilitates communications between applications having different technologies and languages, as well as operating systems. The protocol does so by encoding information in things such as Web requests or responses to messages before they’re sent.  

Soaped up 

According to W3C’s SOAP tutorial, the protocol’s message is an ordinary XML document. It includes an identifier, called an envelope; an optional header; a required body element that contains call/response information; and an optional fault element that describes any message-processing errors. And because SOAP is independent of operating systems or protocols, messages may be transported by various Internet-related protocols. Those may include hypertext transfer protocol (HTTP), simple mail transfer protocol (SMTP), file transfer protocol (FTP) and transmission control protocol/Internet protocol (TCP/IP).  

Automatically staying current with a particular Web information/news source or rapidly syndicating news to the Web are RSS’s selling points. XML-dialect RSS defines an XML-based syntax or set of HTML-like tags. Each RSS feed, also called a Web feed or channel, starts with an tag and ends with an tag. For a simple feed, the item is comprised of a , which is the Web address (uniform resource locator, or URL); and , which is to-be-published content.  

Emerson Process Experts (www.emersonprocessxperts.com)—a blog moderated by Jim Cahill, with Emerson Process Management (www.emersonprocess.com), an Austin, Texas-based process controls vendor—provides useful guidance in an RSS Starter Kit (easydeltav.com/RSSKit/RSSkit_Why.htm). The RSS Advisory Board (www.rssboard.org) notes that RSS files must conform to the XML 1.0 specification, published now in its fourth edition by W3C (www.w3.org/TR/REC-xml). 

What’s handy about RSS feeds is how easily they’re obtained, read and used. To subscribe to feeds, recipients need only click on the RSS icon on the specific Web pages that offer the desired feeds. Reading them requires a Web-based RSS reader, typically offered on the subscription page; for example, Cahill’s blog currently has eight from which to choose. To use feeds, RSS offers the choice of drilling further down with links contained in respective feeds or simply reading the feed and then switching to another.  

Sharing, drilling down or switching channels: Without XML, SOAP and RSS, could we do any now or with such ease? Not for a hypersecond. 

C. Kenna Amos, ckamosjr@earthlink.net, is an Automation World Contributing Editor.
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