What is difference between Rules and validaton in infopath?

I am working on Microsoft office infopath 2007.I have inserted the controls as text box and drop down. when i get right click to control there are 2 option links as Data validation and Rules. what are the main difference in between them? I am new in infopath so need guidance.

when to use r开发者_开发知识库ules and when to use validations. can we customize validation and rules? and can we define custom rules and validation in infopath ?

Data validation can be used to display error alerts when users enter incorrect values into a form. Rather than checking for errors after a form is completed, data validation verifies values as the form is being filled out.

You can use rules to automatically display a dialog box, set a field's value, query or submit to a data connection, switch views, or open or close a form in response to certain events and conditions.

I'm not sure that you can create your own custom rules and data validation. But infopath forms can be customized by writing programming code to respond to form and data validation events, to access and manipulate a form's underlying XML document, to implement custom data submission and merges, and to implement access to external data sources.