Thursday, June 24, 2004

Creating an XML driven web site

An XML driven website is a website that stores the content as XML, either in a file or in a database. When a user requests a page, the XML content is retrieved from the data store and rendered as HTML in the browser. The HTML is usually created by a transformation, such as XSLT, or the HTML can be created programmatically. In either case, the XML data is merged with the markup to create the returned HTML page.

public void GetContent(string loc)
XmlTextReader reader = null;

reader = new XmlTextReader(Server.MapPath(loc));

if (reader != null)
catch(Exception e)
string err = e.ToString();

The nodes in an XML stream can be accessed by an XMLDocument, an XMLTextReader/XMLTextWriter and an XPathNavigator. Each method has its advantages and drawbacks:

* XmlDocument: Provides direct memory access to the entire xml document. Nodes can be selected from the XmlDocument by XPath expressions. Can use a large amount of memory resources.
* XMLTextReader: Provide forward-only access to an xml stream. The entire xml dataset is not loaded into memory all at once, the XmlTextReader reads in nodes on an as-needed basis. The XMLTextWriter writes xml data to a file in a forward-only manner.
* XPathNavigator: Provides bi-directional access to nodes in a XmlDocument or XPathDocument. The XPathDocument provides a fast read-only cache for an xml document. If you are using an XmlTextReader to access the xml, an XPathDocument can be created by passing in a XmlTextReader object into the XPathDocument constructor. This object is not created directly, it is returned from a call to the CreateNavigator() method on the XmlDocument/XPathDocument class.

When inserting text into an XML file, beware of the special characters <, >, ', ", &. They should be escaped by using the special notation.

When passing XML data in memory you can use the following object types:

* XmlNode. Provides an interface to an in-memory tree representation of an XML document. Gives a R/W interface to the XML data structure in addition to XPath expression selections. The XmlDocument inherits the XmlNode abstract class.
* XmlReader. Streaming forward only object. Provides an xml facade over an existing object graph/text/binary data object. Difficult to use.
* XPathNavigator. Traverses xml in a bi-directional manner. Able to navigate an xml document via XPath expressions. This is the preferred way to pass xml around in the CLR.

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