ACDC: An Algorithm for Comprehension-Driven Clustering Vassilios Tzerpos R.C. Holt

Highest cohesion clustering SS1 SS2 SS4 SS11 SS12 SS9 SS10 SS8 SS5 SS6 SS7 SS3

Contents of SS11

Essential comprehension features §Effective cluster naming §Bounded cluster cardinality §Familiarity l Comprehension as pattern recognition l Certain subsystem patterns emerge often in manual decompositions of software systems

Source file pattern Proc3 Proc2 Proc1Proc4 Proc6 Proc5 Var1 Var2 Var3 File1File2

Directory structure pattern File3 File2 File1File4 File6 File5 File7 File8 File9 Dir1Dir2

Body-header pattern alice.c bob.h bob.c alice.h

Leaf collection pattern sin.ctan.ccos.c

Support library pattern busy.cweary.ctired.c

Central dispatcher pattern dispatcher.c

Subgraph dominator pattern dominator.c a.c z.cg.cf.ce.cd.c c.cb.c

The ACDC algorithm §Two stages: l Using a pattern-driven approach, a “skeleton” of the final decomposition is created. Subsystems are named appropriately. l The decomposition is completed by applying an extended version of the Orphan Adoption algorithm

Skeleton construction §Source file clusters §Body-header conglomeration §Leaf collection and support library identification §Ordered and limited subgraph domination §Creation of “support.ss”

Orphan Adoption §Incremental clustering technique §Orphan: a newly introduced resource to a software system §Orphans are adopted by the subsystem that interacts mostly with them §Assuming that a substantial skeleton has been constructed in the first stage, the same technique can be applied here

ACDC properties §Subsystems have familiar or intuitive names §The cardinality of the subsystems is bounded §The final decomposition is nested and unbalanced §Limited use of the directory pattern §Magic numbers not important

Algorithm validation §We experimented with two different software systems, TOBEY and Linux. §We measured the following: l Performance l Stability l Skeleton size l Quality 54 sec84 sec 81.3%69.4% 64.3%51.1% 64.2%55.7%

Conclusions §Clustering approaches should focus on comprehension §Pattern-driven approach appears to perform satisfactorily §Impact of ACDC’s features on comprehension remains to be determined