Constraints and business rules for the input values of the form fields are checked and if necessary an
error message is shown to the user.
See the detailed constraints and business rules in the Functional Specifications Document for more detail.
Upon failure in the provided data, the validation error message is sent back to the client. The input form is displayed again with the filled in data and any error message is displayed under the affected field directly in the form in a highlighted colour. In case error messages are not related to a specific input field (for instance, a global validation involving several form fields), these messages are displayed at the top of form in a highlighted colour. In case of failure, the requested action is not executed, i.e. the data is not saved.