Webservice or just a normal DLL?

[localzuk]

I'm currently implementing the biometric part of our cashless catering system (a c# project), and I have decided to make it independent to the actual program, and have it in it's own database, so I can use it for future projects too (so we would only have to enroll the kids once).

The question I have is this - which, if you were doing this, would you use? A web service? or a standard DLL, for interfacing with the biometrics database?

Both have advantages, and both have disadvantages. So... opinions?

[SYNACK]

The webservice would be vastly more interoperable between diverse systems and is easily encryptable via SSL. It would have a slight performance hit but nothing noticible unless you are processing several thousand a second.

If you are sticking with all windows apps then the DLL could be fractionally easier to code.