General talk about software patterns

["Jan Hannemann" <jan AT cs.ubc.ca>]

Hi all,

Thanks for the great responses. I guess I should have been more clear: my request is a ranking based on the frequency of patterns used, not the how useful they actually are. If current software systems do use a large number of instances of pattern X than that is relevant to everyone using those code bases, regardless of how useful (or appropriate) the pattern is.

In general, the point that pattern usage depends on application domain is important (thanks all who pointed that out). While it is somewhat intuitive, I wasn't aware the differences were that big.

Linda wrote:
> When I was working on the Pattern Almanac, I included references to what I called "experience reports" to show pattern users examples of real-world applications in various domains.

It would be great if you could find that list! Unfortunately I do not have access to the Almanac at the moment.

Ralph wrote:
> The only way to know for sure which patterns are used most is to look at every system in the world.

True. That's why I mentioned this is likely a subjective process and opinions are welcome. The general idea being that if enough experts provide their opinions/experiences, the impression which patterns are more often used would converege somewhat. It seems that, barring domain-specific variance, it actually does. I assume that exmpirical studies (take N real-world systems, count instances of patterns) are a little less subjective even, if those exist at all (I'd be very much interested to hear of those).

Pascal wrote:
> There is also an (unhealthy) feedback loop. Some people use patterns just because they happen to be in the Design Patterns book. (That's probably one of the reasons why Singleton and Visitor are still cited as good examples.) This means that a high number for those patterns doesn't necessarily mean anything. [...]

Only if you are trying to use them to determine pattern quality or appropriate usage of them (and I agree). High numbers for those patters do mean something, though; they mean that these patterns can be found often in software, which makes them important to developers who have to deal with them.

Again, more suggestions/opinions are welcome! Please let us know your experiences with pattern frequency in practice!

Thanks,

--Jan