Subject [firebird-support] Re: How to enforce sort order?
Author Svein Erling Tysvær
>Sort order sequences does not work because it cannot have gaps.
>Do you have a link to the specific faq article that shows how to deal with gaps?

It is quite common to have such a requirement, but when you examine the requirement a bit closer, there's no good reason for it. Of course, sometimes the requirement is real (e.g. you cannot argue with legal requirements, whether or not there is a good reason for the law) and is an old article that discusses unbroken series of numbers.