Hi Jeff,
In Ariba terminology, we call it as Approval Rules which governs the flow of approval process for requisitions. In my project, we do route requisitions based on commodity codes to a specific group, for instance computer software, for any request related to software, all requests are routed through a license manager for that particular company code (based on geographical regions, we have different approvers and hence we have setup different groups / roles for each region i.e. specific to a company code). There is an approval rule defined in our configuration which will just identify if any of the line item is related specifically to Computer Software commodity code and if it is then add license group in the approval flow. We can add multiple validations and approval rules in the system to identify the groups or individuals to which a particular PR should be routed through and also their sequence (sequence like, we have configured our configuration in a way that if actual requester and preparer are different and amount of PR is less than $500 then add actual requester as a watcher otherwise as a first approver in the approval flow).
Please let me know if you need any further information.
Amit