I liked your original answer better because it was a practical answer: "There's no default" :)

However... the ODBC DSNs you mention contain override values for the default server names.

The default dbeng -n server name is the same as the database name. In turn, the default dbeng -n database name is the same as the file name, which in this case is demo.

This can be demonstrated as follows:

Start - All Programs - SQL Anywhere 16 - Personal Server

In the popup window, browse to C:\Users\Public\Documents\SQL Anywhere 16\Samples\demo.db

This method is arguably more direct ( more "default" :) than using an ODBC connection to auto-start a database. It also doesn't specify any values for server or database name, hence the defaults demo and demo.

Well, I had no machine available when I made my comment but have confirmed it now (at least for my setups but I have not modified those):

With SQL Anywhere 12, 16 and 17, both the default ODBC system DSNs for the sample database and the according program menu entries to start the sample database (both 32-bit and 64-bit) do name the server explicitly via -n demo12/demo16/demo17 resp. via supplying that as a connection parameter.

Of course one can override that, but I guess they are different by design to prevent the "mixing" of those databases. (Personally, I use them mostly for answering forum questions, and find myself often with "left open demo databases", and then find that I try to connect to the demo database of another version, noticable by the different server name.)

Of course, YMMV, and I'm still not sure that's the question here at all:)

I used to believe "ODBC Is Evil" but finally saw the light: DSNs are the problem.

...in other words life became easier after I stopped using DSNs altogether :)

And now it's time to

Abandoning DSNs is definitely helpful in the battle to retain sanity.