XML
Using HTML you will almost only have the possibility to present information from a server to browsers. If you want to exchange data, you will need a format, in which you can describe the organization of those data. This format is XML (eXtensible Markup Language),
standardized through World Wide Web Consortium (W3C). Everybody with some knowledge of HTML should recognize some of the features in this example, but as you can see, in XML you define your own tags. In this way it is possible to build your own 'vocabularies'. One of these vocabularies is
XHTML, which actually is HTML 4.01 in XLM disguise. The main difference is that you are forced to create 'wellformed' HTML. This means that all tags must have a finishing tag. For example you can no longer use <BR> but you have to write <BR/> short for <BR></BR>. At the same time you must distinguish between upper and lower case in tag names. That is: </IMG> is not the same as </img>.
You should note the word Stylesheet in the XML example. XML being simply a data format, you must have a possibility to represent these data. This can be done using a matching stylesheet. It has to be written according to the standard XSL (eXtensible Stylesheet Language) and in this case creates the following result. I have
created a small demo of the same data displayed in 3 different ways.
As can be seen from the examples used previously, I am using a tool named
XMLwriter to write XML. XMLwriter has all the features necessary and it is not very expensive. The program makes use of the XML parser from Microsoft to handle and interpret the XML and XSL files. This parser is a part of Internet Explorer version 5.01 or later, which on the other hand means that for the time being only these browsers support XML/XSL directly.
Furthermore the parser must be version 3 or later to fully comply with the standards set up by W3C. The newest version may be downloaded from
Microsoft Download. Here you may also find lots of software related to XML and XSL.
If your browser is Internet Explorer 5.01 or later, you may test the version of the parser used by clicking on TEST.XML. The outcome hopefully looks like this. If this is not the case, the parser is an old version and should be replaced. The newest version may be found at this page.
Another example of the use of XML vocabularies is
RSS. RSS may
be used to fetch headlines and their attached links into you own website as
in this example from BBC.
I have used a parser
written in PHP to do this. You may
find a lot more about newsfeeds at NewsIsFree.
A new format for vector graphics is SVG. Like XHTML it is an XML-implementation. SVG has been made a standard by W3C, but being rather new, it is not yet generally supported by browsers. However, the necessary plugin can be downloaded for free from Adobe. With SVG you can move and scale your drawings without the loss of details known from bitmapped pictures. It is also possible to embed Javascript, giving you all the features of that language. As an illustration of a few of the feature, you may hav a look at this small demo.
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On the Internet you may find lots of information on XML and attached technologies. To the right you will find a few links, that may give you an idea of the reasons XML is going to become the main data exchange technology. Also these links may serve as stepping stones for further exploration. |
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