[DUG] Licencing schemes

[Paul Heinz]

John asked:

> The scheme you mentioned appeals greatly because of its
> simplicity - applies
> to licencing up to a fixed licenced number of concurrent users.  I didn't
> know there was a way to lock one byte - how do you do that??

It's essentially a pair of Win32 APIs (LockFile and UnlockFile). You can
look them up on MSDN for the full details.

function LockFile(hFile: THandle; dwFileOffsetLow, dwFileOffsetHigh: DWORD;
  nNumberOfBytesToLockLow, nNumberOfBytesToLockHigh: DWORD): BOOL; stdcall;

dwFileOffsetHigh and nNumberOfBytesToLockHigh need to be 0 for Win9X
compatibility (if you care).

So, to lock a single byte, pick an appropriate dwFileOffset and use a
NumberOfBytesToLock of 1.

Also, the file doesn't need to be as long as you have 'slots' i.e. it can
even have a size of 0 since you can happily lock any bytes you like, even
those beyond the end of the file.

A gotcha to be aware of is that, in Win32 unlike Unix, you can't read bytes
under a lock so don't lock anything which you will need to be able to read
whilst any locks exist.

> I was more leaning to licencing it per screen installed - it can be more
> costly for the users but as the app is likely to be running much
> of the day that is academic in this case.

Well, we've been using lock-based concurrent user licensing for Profax (and
now Accredo) since ummm.. ages ago i.e. right back to the DOS versions in
the 80s and 90s. Technically, it's pretty hard to beat for simplicity,
reliability, and enforceability.

On the non-technical level, our experience is that customers accept
concurrent licensing as more 'fair'. I think this is simply because they
feel they are paying for _actual use_ and more use equals more business
value which justifies paying more.

Seat-based licensing is generally felt to be somewhat less 'fair' since they
are forced to pay for _potential use_ i.e. because they might _rarely_ need
to use your software from some PC, they have to pay as if they always use it
from that PC.

As seat-based licensing is essentially unenforceable (unless you plan on
demanding to physically audit your customer!) it boils down to an 'honesty'
system and since customers often feel seats-based is less fair, at best they
are likely to only buy as many seats as they actually use or, at worst, they
will cheat and under-license.

So, my opinion is that, without compelling reasons to the contrary, you are
generally better off with concurrent use licensing revenue-wise.

TTFN,
  Paul.