Usability requirements in a tender process

How should the customer specify usability requirements in a tender situation? This is particularly difficult if the product is a standard system with enhancements, since the customer cannot prescribe a specific user interface. Furthermore it must be possible to verify the usability requirements with a reasonable effort, and the requirements must not discourage serious proposers. The paper discusses six different styles of usability specification and shows an example of how to combine them in a complex real life case to meet these goals. The final requirements are presented