Data Validation Rules contain

– A Boolean formula or expression that evaluates the data in one or more fields to either “True” or “False”
– A user defined error message that displays when the rule returns a value of “True”
– Data Validation Rules execute when
– A User Saves a Record
– Before records are imported
– Using the Force.com Data Loader and the Force.com API

Data Validation Rules are enforced on Area Impact
Supported Objects All except Forecasts & Territories
Reporting & Dashboards No impact
API Validation rules enforced via API
Import & Data Loader Validation rules enforced via Import & Data Loader
Lead Convert Validation Rules Enforced – must be turned on in Org
Record Merge Not enforced
Offline & Outlook Editions Validation rules enforced when data is synchronized with server
Salesforce Mobile Validation rules enforced when data is synchronized with server
Web To Case
Web To Lead
Validation rules enforced but no feedback to user
Admin notified of any errors
Self Service Portal Validation rules enforced
Apex Packaging Can be packaged