Last week I subscribed to an online class for XML. This week I received my second class installment. The topic was valid XML documents. This lesson taught that a valid XML document is one that meets the DTD or XML Schema. It is different from an XML document being well formed, which means an XML processor can read the document. To me well formed means it meets the syntax rules of XML.The course notes this week pointed out that XML is a self describing language. So you might not always need a DTD or XML Schema. However when you do use validation, the DTD can be local or public. A validation file such as XML Schema describes the XML document. Then a parser validates the XML document against the schema.
One of the most interesting experiences with this week’s class was an ad on the lesson page. The ad offered a free XML viewer. So I clicked through, then downloaded the Firstobject XML editor. It was a free download. The editor divides the XML document into elements and their sub elements. The tool uses a tree like structure in the user interface. I found the tool to be very basic compared to XMLSpy.
The Firstobject XML editor displays XML as text. There does not seem to be much graphic viewing capabilities other than the tree structure. One nice thing about this product is that the company will give you the source code to the editor if you buy their product. They are trying to sell a single MFC class that does all things XML for $249. That’s a lot cheaper than my XMLSpy tool would cost.
Perhaps the best course of action would be for me to write my own XML viewer and/or editor. Then I would really learn the ins and outs of parsing XML documents. I would not have to start from scratch. I could use an XML parser library to actually read the XML document. This would not be cheating. I would be learn the parser’s API.
