Useful Usable Used Useful Usable Used[NOTE: This page is excerpted from a thread on the patterns-discussion mailing list in July 1998]
The word "pattern" suggests recurrence; if something doesn't recur, it can't possibly be a pattern. But for "Patterns", recurrence is not the sole characteristic of importance. It doesn't prove, for example, that the pattern is any good. Recurrence is a quantitative characteristic, "goodness" is a qualitative one.
Recurrence is a quintessential test that a pattern must pass. It's not the only one, but it is of the pass/fail variety. It is a mandatory precondition, not a qualitative judgement. Recurrence may help lend credibility to the "goodness" of a pattern, but it does not prove goodness; It only reinforces it. If you couldn't somehow make a case for "goodness" in the pattern itself then there is nothing to be reinforced.
Keep in mind that just because something isn't a pattern doesn't mean its not good. If something is a pattern, then (hopefully) it is good. But please let us not fall into the trap of thinking that everything that is good should therefore be a pattern; nor the trap of thinking that something which isn't a pattern can't possibly be good. Don't let the buzzword status of the term "Pattern" lull you into thinking this.
We show that a pattern recurs by showing it is ProvenPractice, and has been UsedThreeTimes (c.f. RuleOfThree). This is what the Known Uses section of a pattern is commonly used for. How do we show that a pattern is good?
To prove "goodness", we must explain the forces, and the resolution of those forces, and why it is a "good" resolution of forces. This is usually done in the Forces/Motivation and in the Resulting Context/Consequences (also known as Resolution of Forces). Oft-times, a pattern also has a Rationale section explaining why the pattern works (not just "how") and why it is good.
In short:
(successful) recurrence ==> the pattern is fit for use
(desirable) resolution ==> the pattern is a useful fit
We need both of these to convince us that the pattern is neither sheer speculation (pure theory) nor is the pattern blindly following others (rote practice). We want to show that the practice is more than just "theory", and that the theory really has been practiced. In fact, one might even say:
A pattern needs to be useful
Because this is how the "pattern in our minds" is transformed into an instance of the "pattern in the world" as a thing that adds value (enhances the quality of life) of a practitioner.
A pattern needs to be usable
Because this is how "the pattern in literary form" is transformed into "the pattern in our minds".
A pattern needs to be used
Because this is how "the pattern in the world" gets to be documented as "the pattern in literary form" in the first place.
These transformations describe an interesting cycle:
from things in the world,
to written things,
to ideas and concepts in our minds,
and back to things in the world,
but now recurring.
Graphically represented
Pattern in literary form
actor: Pattern Writer
^ \
"used" / \ "usable"
/ \
/ v
Pattern in the world<------------Pattern in our minds
actor: Pattern actor: Pattern Reader
Practitioners
"useful"
This page mirrored in WikiPagesAboutWhatArePatterns as of April 29, 2006