928 THE SOFTWARE CONSTRUCTION PROCESS $28.5 of their official interface,given as a short form or deferred version.This aspect of the model is perhaps easier to picture if we rotate the preceding figure,as illustrated below,to emphasize the software layers corresponding to the various clusters,with the more general clusters at the bottom and the more application-specific ones at the top.The design and implementation of each cluster depend only on the specifications of clusters below it,not on their own design and implementation.The figure only shows dependencies on the cluster immediately below,but a cluster may rely on any lower-level cluster. A project's clusters as a set V&V G Cluster n of abstraction layers More application- specific More general V&V G Cluster 2 Client dependency V&V G Cluster 1 TIME 28.5 GENERALIZATION The last task of cluster mini-lifecycles,generalization(the G on the above figure)has no equivalent in traditional approaches.Its goal is to polish the classes so as to turn them into potentially reusable software components. Including a generalization step immediately suggests a criticism:instead of an a posteriori add-on,should reusability concerns not be part of the entire software process? How can one make software reusable after the fact?But this criticism is misplaced.The a928 THE SOFTWARE CONSTRUCTION PROCESS §28.5 of their official interface, given as a short form or deferred version. This aspect of the model is perhaps easier to picture if we rotate the preceding figure, as illustrated below, to emphasize the software layers corresponding to the various clusters, with the more general clusters at the bottom and the more application-specific ones at the top. The design and implementation of each cluster depend only on the specifications of clusters below it, not on their own design and implementation. The figure only shows dependencies on the cluster immediately below, but a cluster may rely on any lower-level cluster. 28.5 GENERALIZATION The last task of cluster mini-lifecycles, generalization (the G on the above figure) has no equivalent in traditional approaches. Its goal is to polish the classes so as to turn them into potentially reusable software components. Including a generalization step immediately suggests a criticism: instead of an a posteriori add-on, should reusability concerns not be part of the entire software process? How can one make software reusable after the fact? But this criticism is misplaced. The a TIME Cluster 2 Cluster n S D I V&V G Cluster 1 S D I V&V G S D I V&V G More More general application￾specific Client dependency A project’s clusters as a set of abstraction layers