Document Object Model

Once an XML parser has done its work, it produces an in-memory representation of the XML. This model exposes properties and methods that let you extract information from and also modify the XML. For example, you will find methods such as createElement to manufacture new elements in the document and properties such as documentElement that bring back the root element in the document (applicationUsers in the example fi le). One of the earliest models used was the Document Object Model (DOM). This model has an associated standard but it does not just apply to XML; it also works with HTML documents. At its heart, the DOM is a tree-like representation of an XML document. You can start at the tree's root and move to its different branches, extracting or inserting data as you go. Although the DOM was used for many years, it has a reputation for being a bit unwieldy and difficult to use. It also tends to take up a lot of memory. For example, opening an XML document that is 1MB on a disk can use about 5MB of RAM. This can obviously be a problem if you want to open very large documents. As a result of these problems, a number of other models have sprung up, especially because the DOM is typically only an intermediate step in processing XML; if its not a goal in itself. However, if you need to extract just a few pieces of information from XML or HTML the DOM is widely supported, especially across browsers, and is used a lot by many of the script libraries that are popular nowadays such as jQuery.