Separation of Concerns. Figure 7 presents the metrics results for the design by
contract concern regarding separation of concerns. It shows that the widely-scoped
crosscutting nature of DbC have presented superior design stability when implemented
using AO techniques. In general, the concern di®usion over components
(CDC) metric is less a®ected on AO implementations as the initial modules seem to
cope well with newly introduced scenarios and the changes are localized in these
modules. The concern di®usion over operations (CDO) metrics also presents a very
superior design stability for the AO implementations. This divergence largely comes
from the quantification properties in AO, where the use of existing pointcut declarations eliminates the need for declaring operations (advice in this case). Even
though the evolution scenario (denoted by the HW release 2) extends the system
with six new use cases, quite few aspect-like methods were introduced. Hence, the AO
design remained stable even when new functionalities are added. The results for
concern di®usion over lines of code (CDLOC) provide additional evidence that AO
implementations present better stability.