XML Reference Guide

Mar 14, 2003

␡

⎙ Print

< Back Page 34 of 278 Next >

So far in this series of entries on the Document Object Model Level 3, I've tried to provide a look at a simple implementation, but for DOM Level 3 Validation, that's not so easy. Xerces almost provides a partial implementation, but it's left over from the experimental implementation of the DOM Level 3 Abstract Schema and Load and Save drafts that were split out into the Validation and Load and Save recommendations.

The end result is that it's hard for me to show you a simple implementation; the implementation report shows only the large systems Oracle, X-Hive and Arbortext. For the sake of completeness, however, I still want to make sure you understand what's available in this specification, which is also available to various degrees in other places.

If you've been reading this series on DOM Level 3, you may wonder why we even need another recommendation for validation. After all, the DOM Level 3 Core does provide some handy capabilites, such as the ability to specify a schema (note the small "s") against which a document should be validated when parsed or at some time afterwards. Well, DOM Level 3 Validation takes things just a little farther than that.

The most striking difference is that while the validation capabilites in the Core are geared towards finding out whether a document you're loading conforms to a particular schema, the Validation recommendation is geared towards making it easier to actually work with a document without making it invalid.

Now, don't get me wrong, both recommendations enable you to validate a document that already exists, and to specify that no changes should be made to the document unless they are within the boundaries defined by the schema. But the Validation recommendation enables you to perform tasks such as determining the validity of a single node or tree of nodes, or even character data. It also provides the ability to determine just what changes you can make to a particular node.

Perhaps the best way to get a feel for what we have here is to look at the interfaces that the recommendation defines:

A NodeEditVAL is also, as specified, a Node, just as a DocumentLS is also a Document. But in addition to the normal operations you can perform with a Node, such as appendChild() or insertBefore(), a NodeEditVAL provides operations such as canAppendChild() and canInsertBefore(), which enable you to test the proposed operation against the required structure before performing it. It also provides you with the defaultValue, if applicable, or the enumeratedValues, in the case of multiple possiblities. The NodeEditVAL interface also lets you check the nodeValidity.

The ElementEditVAL extends NodeEditVal, and is designed to assist in editing elements. For example, it provides attributes such as allowedChildren, allowedFirstChildren, and allowedNextSiblings, as well as methods such as canSetAttribute() and canSetTextContent().



The CharacterDataEditVAL also extends NodeEditVAL.
It provides guidance on editing the text of a node, with methods such as
canSetData(), canAppendData() and canDeleteData().
It also provides a isWhitespaceOnly() method that helps you determine
whether you can safely ignore the node altogether.

The DocumentEditVAL interface also extends NodeEditVAL,
and an object implementing it must also implement the Document interface.
It provides the continuousValidityChecking attribute, which controls
whether you can make changes that violate the schema, as well as the validateDocument()
method, which lets you validate the document after it already exists.
It also provides the getDefinedElements() method, which
provides the names of all of the "globally defined" elements for a
particular namespace.  These are elements that are defined independently of
their context, and can theoretically be used anywhere in the document.

This is by no means a complete look at everything in the recommendation, but
it should be enough for you to have a good grasp of what it's all about so that if
the DOM Level 3 Validation Recommendation looks like something useful to you, you
can read through it with a good understanding of what it's all about.


            
                    
            < Back
        Page 34 of 278
            Next >
    

                
                    
                        
                            🔖 Save To Your Account


    

    
        
            
                InformIT Promotional Mailings & Special Offers

                
                    
                        ⚠
                    
                
                
                    

                    
                
                
                    
                        
                    
                
                
                    
                        
                            I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.
                        
                    
                    
                    
                        Email Address