Yes, this is possible. Writing SQL provider might be simpler, because API here is more or less stable (there are already 4 SQL providers).

In general, you should implement two parts:

• SQL DOM provider. See e.g. PostgreSQL SQL DOM provider to estimate the complexity. There are about 100 Kb of C# code for PostgreSQL. SQL Server and Oracle providers contain about 75 Kb of C# code each.
• Storage provider. DataObjects.Net is independent from SQL DOM, but it provides base classes for any SQL DOM-based provider. Since these classes are already there, impementation of each particular provider is relatively simple: e.g. PostgreSQL storage provider contains just 3 Kb of code.

First part is the most complex one: full-featured provider implementation requires deep knowledge of underlying database. On the other hand, there are 4 working providers and tests for them, as well as huge test suite for DO4 itself.

Benefit: if you're talking about Sybase Advantage Database Server, we're ready to provide free Ultimate license with subscription to all future upgrades for this product for even partially working version of provider for it. And certainly, we're ready to help you to develop it (Q/A).

You can check out v4.2 codebase to study everything deeper. Last chapter of Manual explains how to build DO4 from source code. I'd also prefer if this branch would be updated by you:

• It's quite easy now to grant anyone write access to this repository. But the same isn't true for v4.3 repository - until final release it will be closed at all
• SQL DOM stays almost unchanged during last year or even two
• We integrate all the changes made to this branch into v4.3 on daily basis.

Any further questions are welcome.