The event passes the row to you, along with a value indicating what type of action (change, insert, and so on) is being performed.The Column Changing, Row Changing, and Row Deleting events are raised during the update process.
For more information, see How to: Validate Data During Column Changes or How to: Validate Data During Row Changes.
For a complete example, see Walkthrough: Adding Validation to a Dataset.
Additionally, if your data is structured so that the value of one column is validated based on the contents of another column, then perform your validation during the Row Changing event.
When records are updated, the Data Table object raises events that you can respond to as changes are occurring and after changes are made.
Because the dataset is part of your application (unlike the database backend), it's a logical place to build application-specific validation.