This is the fifth in a series of articles explaining XML in layman's language, being particularly careful to avoid the use of technical jargon.
The first article in the series provided the following brief definition of XML:
XML gives us a way to create and maintain structured documents in plain text that can be rendered in a variety of different ways.
Then the article proceeded to break down the jargon into plain English and provided some examples of structured documents.
In the previous articles in this series, I have introduced you to tags, elements, content, and attributes. I have discussed tags, attributes, and elements in detail. I promised to take up content in this article.
Of the four terms mentioned above, content is the easy one. As I mentioned in an earlier article, sandwiched in between the beginning tag and the end tag of an element, we find the raw information (content) that the XML document is designed to convey. In other words, this is where we put the information for which the document was created.
For example, if the XML document is being used for creation and maintenance of material for a newspaper, the content constitutes the news. If the XML document is being used for creation and maintenance of a Java programming textbook, the content contains the information about Java programming that we want to present to the student.
The content is the raw information. The tags, attributes, and elements define the structure into which we insert that information.
As mentioned in an earlier article, one of the primary objectives of the use of XML is to separate content from presentation. If we insert the raw material as content into a structure defined by the tags, elements, and attributes, then that raw material can be presented in a variety of ways.
For example, an XML document can be used to represent a newspaper. Then, given two different rendering engines, that same document can be presented as an ordinary hard-copy newspaper by printing the content on newsprint in a format defined by the structure.
The same XML document can be used to present the same information in a completely different format on a computer screen. In both cases, the rendering engine would examine the structure defined by the tags, elements, and attributes and would then format and present the news (content) in a format appropriate for the presentation media being used.
Note that even though the same XML document could be used for these two presentations, it is very likely that two different rendering engines would be used. One rendering engine would be designed to present the news on newsprint, and the other rendering engine would be designed to present the news on a computer screen.
At this point, you may be saying "So What! Fads come and go. XML may be just another fad."
I don't believe that XML is just another fad, and I base this belief on the fact that both Microsoft and IBM have adopted XML as an important part of their future. For example, here are some of the things that Simon Phipps, IBM's chief XML and Java evangelist had to say recently in his keynote speech at the Software Development East conference.
"Because it allows companies to share information with customers or business partners without first negotiating technical details, Extensible Markup Language (XML) will grease the skids of electronic business and become the assumed data format at the end of 2001."
"Other successful Internet technologies let people run their systems without having to take into account another company's own computer systems, notably TCP/IP for networking, Java for programming, and Web browsers for content delivery. XML fills the data formatting piece of the puzzle."
"These technologies do not create dependencies. It means you can build solutions that are completely agnostic about the platforms and software that you use."
In the speech, entitled "Escaping Entropy Death" Phipps noted that users are reaching the point where the cost of simply owning some systems is exceeding the value it provides.
"The key benefit to IT managers that adopt XML and other non-proprietary standards is that they will greatly reduce the cost of maintaining a computer's systems and will allow them to extend existing systems."
"In the next decade, you can't just ask when can you have [a new application]. You also have to ask how much will it cost to own."
"The solution, interestingly enough, is not constant innovation. You have to redeem the best of the parts you have and combine them with the best of the future."
Phipps contended that the IT industry has moved on from the
era of vendor-imposed standards.
In upcoming articles, I will be discussing such topics as well-formed documents, valid documents, and the DTD.
Trying to wrap your brain around XML is sort of like trying to put an octopus in a bottle. Every time you think you have it under control, a new tentacle shows up. XML has many tentacles, reaching out in all directions. But, that's what makes it fun. As your XML host, I will do my best to lead you to the information that you need to keep the XML octopus under control.
This HTML page was partially produced using the WYSIWYG features of Microsoft Word 2000. The images on this page were used with permission from the Microsoft Word 97 Clipart Gallery.
Copyright 2000, Richard G. Baldwin