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| <h1>The XML C library for Gnome</h1> |
| <h2>Validation, or are you afraid of DTDs ?</h2> |
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| <p>Well what is validation and what is a DTD ?</p> |
| <p>Validation is the process of checking a document against a set of |
| construction rules; a <strong>DTD</strong> (Document Type Definition) is such |
| a set of rules.</p> |
| <p>The validation process and building DTDs are the two most difficult parts |
| of the XML life cycle. Briefly a DTD defines all the possibles element to be |
| found within your document, what is the formal shape of your document tree |
| (by defining the allowed content of an element, either text, a regular |
| expression for the allowed list of children, or mixed content i.e. both text |
| and children). The DTD also defines the allowed attributes for all elements |
| and the types of the attributes. For more detailed information, I suggest |
| that you read the related parts of the XML specification, the examples found |
| under gnome-xml/test/valid/dtd and any of the large number of books available |
| on XML. The dia example in gnome-xml/test/valid should be both simple and |
| complete enough to allow you to build your own.</p> |
| <p>A word of warning, building a good DTD which will fit the needs of your |
| application in the long-term is far from trivial; however, the extra level of |
| quality it can ensure is well worth the price for some sets of applications |
| or if you already have already a DTD defined for your application field.</p> |
| <p>The validation is not completely finished but in a (very IMHO) usable |
| state. Until a real validation interface is defined the way to do it is to |
| define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> |
| external variable to 1, this will of course be changed at some point:</p> |
| <p>extern int xmlDoValidityCheckingDefaultValue;</p> |
| <p>...</p> |
| <p>xmlDoValidityCheckingDefaultValue = 1;</p> |
| <p> |
| <p>To handle external entities, use the function |
| <strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to |
| link in you HTTP/FTP/Entities database library to the standard libxml |
| core.</p> |
| <p>@@interfaces@@</p> |
| <p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p> |
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