3. Error conditions

Each operation on the calendar system has a number of pre-conditions and post-conditions that apply.

A “precondition” for a method describes the state of the server that must be true for that method to be performed. A “post-condition” of a method describes the state of the server that must be true after that method has been completed. Any violation of these conditions will result in an error response in the form of a CalWS XML error element containing the violated condition and an optional description.

Each method specification defines the preconditions that must be satisfied before the method can succeed. A number of post-conditions are generally specified which define the state that must exist after the execution of the operation. Preconditions and post-conditions are defined as error elements in the CalWS XML namespace.