What is XPATH?

XML Path Language is a W3C specification that defines syntax for addressing parts of XML document. XML document is considered as a logical tree structure, and syntax based on this consideration is used to address elements and attributes at any level in the XML document.

For example, considering the XML document described above in answer to question 2, /abc:Employees/abc:Emp/@EmpID XPath expression can be used to access the EmpID attribute under the Emp element under the Employees document element.

XPath is used in various other specifications such as XSLT.

Why do we get errors when we try to serialize a Hashtable?

XmlSerializer will refuse to serialize instances of any class that implements IDictionary, e.g. Hashtable. SoapFormatter and BinaryFormatter do not have this restriction.

Why is XmlSerializer so slow?

There is a once-per-process-per-type overhead with XmlSerializer. So the first time you serialize or deserialize an object of a given type in an application, there is a significant delay.

This normally doesn't matter, but it may mean, for example, that XmlSerializer is a poor choice for loading configuration settings during startup of a GUI application