What is the definition of a Volatile Class?
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From: MikeB on 31 Dec 2009 05:53 A colleague has been reading Robert C Martin's "Agile Principles, Patterns, and Practices in C#". In the "Factory chapter", Robert Martin uses the term "Volatile Class" but neither me nor my colleague are sure what he means by that. Google reveals little. Is it just a class that is likely to be prone to change or is it something else entirely? TIA, MikeB
From: S Perryman on 31 Dec 2009 06:45 MikeB wrote: > A colleague has been reading Robert C Martin's "Agile Principles, > Patterns, and Practices in C#". In the "Factory chapter", Robert Martin > uses the term "Volatile Class" but neither me nor my colleague are sure > what he means by that. > Google reveals little. Is it just a class that is likely to be prone to > change or is it something else entirely? Volatility (V) is a statement of the likelihood of change in a given time period. Its converse property is impact (I) , the likelihood that of change propagating to a dependent. V and I are inversely proportional. For any entity E, the greater the value of I(E) (the likelihood that a change to E will cause change propagation to the dependents of E) , the lower the tolerable value of V(E) . A good measure of entity 'stability' is : 1 - ( I(E) * V(E) ) Impact is a *structural* property (based on the nature of dependencies) . Volatility is a *temporal* property (based on the period of observed change : product release, development iteration etc) . Regards, Steven Perryman
From: MikeB on 31 Dec 2009 21:00 S Perryman wrote: > V and I are inversely proportional. Eh? Where does that assertion come from?
From: MikeB on 1 Jan 2010 06:23 MikeB wrote: > S Perryman wrote: > >> V and I are inversely proportional. > > Eh? Where does that assertion come from? Steven, the reason I questioned what looked like an assertion was that I've been exposed to codebases where both V and I are high. Those systems invariably exhibited poor design. Taking this further, I'd venture that for a given volatility, impact is a purely function of the quality of the design. I wonder whether I misunderstood you and you meant that "in a good design, V and I are inversely proportional". Regards, MikeB
From: Daniel Pitts on 1 Jan 2010 12:10
MikeB wrote: > MikeB wrote: >> S Perryman wrote: >> >>> V and I are inversely proportional. >> >> Eh? Where does that assertion come from? > > Steven, > > the reason I questioned what looked like an assertion was that I've been > exposed to codebases where both V and I are high. Those systems > invariably exhibited poor design. > > Taking this further, I'd venture that for a given volatility, impact is > a purely function of the quality of the design. > > I wonder whether I misunderstood you and you meant that "in a good > design, V and I are inversely proportional". It could be that Steven meant that there is a lower bounds on V*I, but that is only my guess, I have nothing to back that up. -- Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> |