Ward,
A sword can be used to thrust (rapier) or cut (broadsword), or slice (saber), or chop (cutlass).
Neat thing? These are all ENGLISH words. Dagger is similarly an ENGLISH word.
The problem here is translation. Even among people who speak English, sword and dagger are defined differently, often subjectively, and often for different and contradictory purposes. The Australian law that Alan quoted above isn't THE definition, it's a rule for a policeman. Collectors will see things differently.
Who's right? No one is. The issue is translation. Sword and dagger are as much culture-bound concepts as jambiya. An English dagger isn't quite the same thing as a Philippine daga, although they have similar cultural and linguistic roots.
We get stuck, because English is the common language for the collectors who post here, and without thinking, we tend to assume that concepts in English are the standard to which everything must be translated. That doesn't work so well in practice. A jambiya isn't just an ornamented hunk of steel, it is a tool and an identity symbol. If you want to understand it, you need to know something about the Muslim culture it's embedded in.
As for uses, I'll admit that the only uses I've ever seen for a jambiya (on TV) are: a) dancing (as Khanjar showed above) and b) clearing debris out of a qanat (
link) so that the water would flow freely (and I admire the men who waded through kilometers of muddy water to do the clearing). If I was to stupidly assume that that was all you could do with a jambiya, I'd suggest both that length was irrelevant and that calling it a sword was silly. Similarly, it's also myopic to assume that fighting is the only real function for a jambiya, and that is how it should be categorized in English: sword or dagger. It's a jambiya. Traduttore traditore.
Best,
F