Data validation lets you control data that is entered into an application by ensuring that the data conforms to specific type or formatting rules. Validation techniques have the following features:

• They let you provide feedback to users so that they can immediately correct information they provide. For example, a form can provide immediate feedback when a user enters a name in a telephone number field, or the form could force the user to enter the number in the correct format.
• They help prevent application errors that might arise when processing invalid data. For example, a validation test can prevent a variable that is used in a calculation from having nonnumeric data.
• They can help enhance security by preventing malicious users from providing data that takes advantage of system security weaknesses, such as buffer overrun attacks.

ColdFusion provides several techniques to ensure that data is valid. These include techniques for validating form data and for validating ColdFusion variables. They also include techniques for validating form data before the user submits it to ColdFusion, or on the ColdFusion server.

When you design data validation you consider the following factors:

The validation technique: Whether to validate on the client's browser or on the server, and the specific server- or client-side validation technique, such as whether to validate when a field loses focus or when the user submits the form.

The validation type: The specific method that you use to validate the data, including the rules that you apply to test the data validity, such as testing for a valid telephone number.

The following sections describe the ColdFusion validation techniques and provide information on selecting a technique that is appropriate for your application. They also describe the validation types that ColdFusion supports. Later sections describe particular techniques in detail.