z-index property: 9.5. Stacking Positioned Elements
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You can generate the XML yourself (from your object model). If you created an object model that simply imports information from your XML document (using SAX or DOM), you would have to write a class that would convert your object model into an XML file (or set of XML files). This class would have to create an ApplicationML file that contains the information in your Java object model (which is in memory). Since this object model is not an adapter on top of DOM, it is not possible to use the DOM parser to generate the XML for you. You can use the DOM parser to generate the XML for you if you created an object model that is an adapter on top of DOM. Since your object model uses the document object tree, all the information contained in it is actually stored in the tree. The XML parser can take this tree and convert it to XML for you, you can then save this generated XML to a file. So the DOM parser can generate the ApplicationML file for you.
There are advantages and disadvantages to using some of the strategies to import and export XML. The complexity of your application data and available system resources are factors that would determine what strategy should be used.
Client and Server side - Application Servers
When you create your data using an XML editor (that you can write), you can not only input the content of your data, but also define the structural relationships that exist inside your data. By allowing you to define your own tags and create the proper structural relationships in your information (with a DTD), you can use any XML parser to check the validity and integrity of the data stored in your XML documents. This makes it very easy to validate the structure and content of your information when you use XML. Without XML, you could also provide this validation feature at the expense of developing the code to this yourself. XML is a great time saver because most of the features that are available in XML are used by most programmers when working on most projects.
By using XML and Java, you can quickly create and use information that is properly structured and valid. By using (or creating) DTDs and storing your information in XML documents, you have a cross-platform and language independent data validation mechanism (for free) in all your projects!
You might use XML to define file formats to store information that is generated and used by your applications. This is another use of the structured nature of XML. The only limitation is that binary information can't be embedded in the body of XML documents. For example, if you wrote a word processor in Java, you might choose to save your word processor documents to an XML (actually your ApplicationML) file. If you use a DTD then your word processor would also get input file format validation as a feature for free. There are many other advantages to using XML and a file storage format for your applications which will be illustrated later in the chapter.
Here are some benefits of the structured nature of XML:
Figure 8-15. Centering an element with automatic margins
As of this writing, only Internet Explorer 4.5 and 5 for the
Macintosh and Opera 3.6 will center elements using
The other possibility is when one of the margins and the width are
set to be auto. In this case, then the margin set
to be auto is reduced to zero: