I got to use WCF callbacks recently and realized some of it's gotchas , which are listed here: Callbacks requires communication over duplex channel Requires all clients to implement the callback interface, exposed by the service BasicHttpBinding...

Just to be clear, there are 5 types of a SQL joins: Cross-join or Cartesian Product - Joins all rows from one relation with rows from the other relation Inner join - Joins only those rows that have same data in the common attributes of the two...

If you install Visual studio 2008 while the 2005 version exists, and you have a website project that uses ajax, you're bound to run into the following issue: You'll see an error saying: "Ambiguous reference of System.UI.Web.Extensions.dll found" ....