Traditionally performance modellers have tended to ignore the difficulty of obtaining parameter vaules which represent the resource demands of multi-layered software. In practice the use of performance engineering in large-scale systems development is limited by the cost of acquiring appropriate performance information about the various software components. However, if this information cart be reused when components are combined in different ways, then the cost of measurement can be more easily justified. Such reuse can be achieved by means of a composite work model.