Decision Models are a tool for Decision Analysis and neither have workflow.

Workflows will usually include decision points. If the decision is non-trivial some decision analysis is required. That's a whole set of artefacts associated with one diamond in the workflow.

Say hello to decision trees, zwicky boxes and a whole fascinating galaxy of evaluation, assessment, simulation, etc. tools and techniques.  It won't hurt to start by googling "decision analysis" and "uncertainty".  Portfolio analysis is a sub-genre of this, but since it involves money, it's thorough and well documented.

Another good place to start is Sam Savage's "Flaw of Averages", Excel and a copy of XLSim. Have fun--it's a fun topic.