In the following two articles, I'm going to wrap up my pondering on XML. We'll explore the basic schema of a DTD, and the future of XML.
Let's recall that some basic features of XML are:
· XML can keep data separated from your HTML · XML can be used to store data inside your HTML documents · XML can be used as a format to exchange information · XML can be used to store data in files or in databases
The power and beauty of XML is that it maintains the separation of the user interface from structured data, allowing the seamless integration of data from diverse sources. Customer information, purchase orders, research results, bill payments, medical records, catalog data and other information can be converted to XML on the middle tier, allowing data to be exchanged online as easily as HTML pages display data today. Data encoded in XML can then be delivered over the Web to the desktop. No retrofitting is necessary for legacy information stored in mainframe databases or documents, and because HTTP is used to deliver XML over the wire, no changes are required for this function.
Once the data is on the client desktop, it can be manipulated, edited, and presented in multiple views, without return trips to the server. Servers now become more scalable, due to lower computational and bandwidth loads. Also, since data is exchanged in the XML format, it can be easily merged from different sources - ok, this is the aspects that personally interests me. The portability of data. Database programmer all over the world face unlimited problems while tackling with data of multifarious formats. If formats cease to matter, anybody, anywhere, on whichever machine, can view and manipulate the data.
>From the previous article, we might recall the XML, unlike HTML, does not have proprietary tags. We can go on a wild trip and define our own tags, according to the necessity. Consider this for example:
<?xml version="1.0"?> <my-schedule> <date>4/17/2001</date> <morning-to-noon> <XML-tutorial> <XML-Introduction>Telling what exactly XML means</XML-Introduction> <XML-Examples>Some Examples of XML</XML-Examples> <XML-Conclusion>Some concluding text</XML-Conclusion> <XML-Email>Email the XML files to Yagna</XML-Email> </XML-tutorial> </morning-to-noon> <noon-to-mid-noon> <nothing-important> Have something light to eat and laze around </nothing-important> </noon-to-mid-noon> <mid-noon-to-evening> <work>Work on a client's web site</work>
</mid-noon-to-evening> ............ <date>4/18/2001</date> .............. </my-schedule>
If you can't make out what this is all about, don't worry. This is just an imaginary schema of a data structure that can be represented through an XML document.
Before you get the time to come to grips with the gory XML introduction, I present a more evolved version of the above mentioned XML code:
<?xml version="1.0"?> <!DOCTYPE my-schedule [ <!ELEMENT my-schedule (date +)> <!ELEMENT date (morning-to-noon, morning-to-mid-noon, mid-noon-to-evening)> <!ELEMENT morning-to-noon (XML-tutorial)> <!ELEMENT XML-tutorial (XML-Introduction, XML-Example, XML-Conclusion, XML-Email)> <!ELEMENT XML-Introduction (#PCDATA)> <!ELEMENT XML-Example (#PCDATA)> <!ELEMENT XML-Conclusion (#PCDATA)> <!ELEMENT XML-Email (#PCDATA)> <!ELEMENT noon-to-mid-noon (nothing-important)> <!ELEMENT nothing-important (#PCDATA) <!ELEMENT mid-noon-to-evening (work +)> <!ELEMENT work (#PCDATA) ]> <my-schedule> <date>4/17/2001</date> <morning-to-noon> <XML-tutorial> <XML-Introduction>Telling what exactly XML means</XML-Introduction> <XML-Examples>Some Examples of XML</XML-Examples> <XML-Conclusion>Some concluding text</XML-Conclusion> <XML-Email>Email the XML Article</XML-Email> </XML-tutorial> </morning-to-noon> <noon-to-mid-noon> <nothing-important> Have something light to eat and laze around </nothing-important> </noon-to-mid-noon> <mid-noon-to-evening> <work>Work on a client's web site</work>
</mid-noon-to-evening> ............ <date>4/18/2001</date> .............. </my-schedule>
The above is a comprehensive example of a DTD - Document Type Definition. XML provides an application independent way of sharing data. With a DTD, independent groups of people can use a common DTD for interchanging data. Your application can use a standard DTD to verify that the data you receive from the outside world is valid. You can also use a DTD to verify your own data.
In this example, the data structure is well defines. Each parent node has a child node, and some child-nodes have grand-child nodes and so on.
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