DOM tree

1, DOM tree

All types of XML parsers require processing objects to "well" XML documents, some can also validate according to DTD or XML Schema, the DOM (DOCUMENT OBJECT MODEL) parser analyzes XML documents to generate a one-time Objects in memory are used to describe the document.

The DOM is an interface-independent interface that allows programs and scripts to dynamically access and modify the content, structure, and type of documents. It defines a series of objects and methods to perform a variety of random operations for DOM trees:

● Document Object: As the highest node of the tree, the Document object is an entry for the entire document.

● Element and Attr object: These node objects are mapped to a part of a document, and the set level of the node just reflects the structure of the document.

● Text object: As the child node of the Element and Attr object, the Text object expresses the text content of the element or attribute. The Text node no longer contains any child nodes.

● Collect index: DOM provides several set indexing methods, which can be traversed in the specified manner. Index parameters are starting from 0.

All nodes in the DOM tree are inherited from the Node object. The Node object defines some of the most basic properties and methods, using these methods to realize the traversal of the tree, and at the same time, the name of the node can be known according to the attribute, and the value is judged.

With DOM, developers can dynamically create XML, traverse documents, increase / delete / modify document content. The API provided by the DOM has nothing to do with the programming language, so the implementation method of different parsers may also be different for interfaces that have no clear definitions in some DOM standards. For convenience, the examples of this article use the MSXML DOM scheme and write code with VB Script.

2, the structure of the DOM tree

After the Document object is established, you can contact the XML document or data island. The loading method of the data island is to assign the data island ID to the Document object:

Set doc = dsoDails.xmldocument

The loading document is generally divided into three steps:

1. Create an analyzer instance using the CreateObject method;

2. Set the async property to false, prohibiting asynchronous loading, so when the document is loaded, the control will return to the calling process. If you want to get a document loading status, you can read the readyState property value;

3. Use the LOAD method to load the specified document.

SET DOC = CreateObject ("Microsoft.xmldom")

Doc.async = false

Doc.Load "Books.xml"

XML DOM also provides a way to loadXML to load an XML string into a DOM tree. When using the XML string directly as the parameters of the method.

3, DOM Tree Access

You can use the DocumentElement property to access the root element using the DocumentElement property after the document is loaded:

Set rootnode = doc.documentelement

Once a reference to a node (eg, root node) in the DOM tree is established, the appropriate method can be traversed according to the level relationship between the nodes.

The following is the use of Books.xml as an example: