[ryzhyk]

I'd say the difference is in the type of transaction isolation guarantees each system provides. DBSP can process multiple diffs in parallel, and when it's done it outputs a single diff that captures the effects of all the input diffs. DD can additionally attribute each output diff to a specific input diff by assigning each input diff and matching output diff a logical timestamp. This has a cost in terms of complexity and runtime overhead, but it allows strong isolation of concurrent transactions.

[ryzhyk]

But as gz09 said, both DD and DBSP are data-parallel architectures that can evaluate queries concurrently on multiple threads or multiple machines.