Validating xml using dtd chritian dating relationships
So now you know that a DTD is a requirement for a valid document. What happens when you run the parser on your current version of the slide presentation, with the DTD specified? That code is reproduced here: is a validation error, although you have seen that it can also be generated if the file specifies a version of XML that the parser is not prepared to handle.
Remember that your application will not generate a validation exception unless you supply an error handler such as the one here.
To see what happens when the XML document does not specify a DTD, remove the declaration. Because you don't yet have one, it's value is null.
In other words, the message is saying that you are trying to validate the document, but no DTD has been declared, because no declaration is present. (In the next section, you'll learn how to define parameter entries so that we can use XHTML in the elements we are defining as part of the slide presentation.) It is important to recognize that the only reason an exception is thrown when the file fails validation is as a result of the error-handling code you entered in the early stages of this tutorial.
It contains a reference to an XSD file, which you will also need to copy from below or download and enter into the webpage (in a second step, when you are prompted for it) to see the validation results.
HTML browsers are allowed to display HTML documents with errors (like missing end tags). A "well formed" XML document is not the same as a "valid" XML document. In addition, it must conform to a document type definition.Now that you know how to use an XML Schema definition, we'll turn to the kinds of errors you can see when the application is validating its incoming data.To do that, you'll use a document type definition (DTD) as you experiment with validation.To be notified of validation errors in an XML document, the parser factory must be configured to create a validating parser, as shown in the preceding section.In addition, the following must be true: You'll learn more about namespaces in Validating with XML Schema.
For now, understand that schema validation is a namespace-oriented process.