Re: [wsn] Analysis of filtering

[David Hull <dmh@tibco.com>]

Steve Graham wrote:

> For example, suppose dmhFilter has a "suppress all but every Nth message" option.  
> This seems like a perfectly reasonable, if arbitrary, filter on its own.  But it
> won't commute with anything.
Then whoever specifies the dmhFilter MUST state that the dmhFilter MUST be placed
last in the list of expressions to be evaluated.

The point was that such a filter could legitimately be used either before or after some other filter, with differing but equally legitimate effects.  Restricting it to some particular position just de-legitimizes one of those effects, for no apparent reason.

As far as I can tell, the requirement of commutativity is too strict.