The paper describes a language called PCL, which has been designed to
model the architecture of multiple versions of computer-based systems
(system families), PCL has evolved from module interconnection languag
es, and its novel features include the ability to model the variabilit
y between members of a system family and facilities for the integrated
modelling of hardware, software and documentation structures, The fea
tures of PCL are illustrated using a number of simple examples. A supp
orting toolset for PCL has been implemented and is briefly described.