How do I simulate an auto-increment field in a Domino database?
Because of the distributed nature of Notes applications, where you can have different replicas on different servers or even on a user's local hard drive, assigning a unique sequential number as a document is being composed is not as straightforward as in a single-server, relational environment. This topic has been discussed extensively in the Notes 4 & 5 forum on LDD. Go there and search for "sequential numbering" and I think you will find dozens of solutions, applicable to different situations.
Incidentally, in my experience designing Notes applications, I've found that very often a requirement initially stated as a sequential identifier, can be satisfied with a value that's not sequential but merely unique (e.g., using the @Unique function).