Ken,

I accept your criticism of the use of boolean discriminator attributes.  There are other mechanisms (such as an IsInClass function using bitwise operators) that would allow for the implementation of richer classification mechanisms – but I thought that it would distract from the intention of the article.

The use of some other field, as opposed to an attribute within the xml fragment is redundant but is intended for some performance gain by not having to query the xml directly in order to retrieve the initial subset that you may be interested in and therefore I would avoid having classification structures contained solely within the xml itself.

Simon