XPathDocument vs XmlDocument

XmlDocument	XPathDocument
- Based on W3C DOM Model - Loads entire Xml in memory - Read/Write - Slower than XPathDocument - Support for XPath/XSLT - Supports both XPathNavigator and DOM interfaces	- Based on XPath Data Model - Loads entire Xml in memory - Read Only - Faster than XmlDocument - Optimized support for XPath/XSLT - Supports only XPathNavigator interfaces

XmlDocument is based on the W3C XML DOM, which is an object model that basically covers all XML syntaxes, including low-level syntax sugar such as entities, CDATA sections, DTD, notations, etc. That's a document-centric model and it allows for full fidelity when loading/saving XML documents.

XPathDocument is based on an XPath 1.0 data model that is a read-only XML Infoset-compatible data-centric object model that covers only semantically significant parts of XML, leaving out insignificant syntax details - no DTD, no entities, no CDATA, no adjacent text nodes, only significant data expressed as a tree with seven types of nodes.

Simple and lightweight. That's why XPathDocument is a preferred data store for read-only scenarios, especially with XPath or XSLT involved.

Reading an Xml

1. Parsing the XML 1.0 byte stream

a. XmlTextReader : Parses the XML 1.0 Byte Stream and the complexities of the XML 1.0 syntax by serving up the document as a logical-tree structure through higher-level APIs.

- Performance - Memory - Traversal - Operation - XPath - XSLT

- Fastest - Most efficient as only one node needs to be in memory - Forward Only - Read Only - No - No

2. Processing the Logical Tree via XML APIs

i. Streaming

a. XmlReader

- Models read an Xml as a forward-only, linear stream of nodes.
- XmlReader allows the client to pull the nodes one at a time much like the firehose cursor model in data access technology.


ii. Traversal Oriented

a. XmlNode (XmlDocument)

- Built on top of XmlReader

- Performance - Memory - Traversal - Operation - XPath - XSLT

- 2 to 3x slower than XmlTextReader - Loads entire Xml/Tree Structure in Memory - Full Traversal - Read/Write - Yes - No

b. XPathNavigator

- Uses a cursor model, which gives the underlying implementation more options in terms of how the tree is actually stored.

- Performance - Memory - Traversal - Operation - XPath - XSLT

- Faster than XmlDocument - More efficient than XmlDocument - Full Traversal - Read Only - Yes - Yes

3. Choosing which class

• What kind of reader should I use?
  Use XmlTextReader if:
  * Performance is your highest priority and…
  * You don't need XSD/DTD validation and…
  * You don't need XSD type information at runtime and…
  * You don't need XPath/XSLT services
  
  Use XmlValidatingReader if:
  
  * You need XSD/DTD validation or…
  * You need XSD type information at runtime or…
• Should I load the tree into memory?
  
  Use the DOM if:
  
  * Productivity is your highest priority or…
  * You need XPath services or…
  * You need to update the document (read/write)
• XmlDocument or XPathDocument?
  * You need to execute an XSLT transformation or…
  * You want to leverage an implementation (like XPathDocument)