What is a checkpoint and what are different types of checkpoints?

Checkpoints allow you to compare the current behavior of the application being tested to its behavior in an earlier version. There are four types of checkpoints.
i. GUI checkpoints verify information about GUI objects. For example, you can check that a button is enabled or see which item is selected in a list.
ii. Bitmap checkpoints take a “snapshot” of a window or area of your application and compare this to an image captured in an earlier version.
iii. Text checkpoints read text in GUI objects and in bitmaps and enable you to verify their contents.
iv. Database checkpoints check the contents and the number of rows and columns of a result set, which is based on a query you create on your database.