If you are developing a Component, i.e., a set of rulesets assembled for specific reuse purpose, you would want to be careful to declare which rulesets a given ruleset is dependent on within that Component.
If a Component were developed in AV mode such that it only works correctly due a ruleset that is outside the RV dependency list, that Component would fail when deployed to a different Application.
RSV (Ruleset Based Validation) Vs ABV (Application Based Validation)
In ABV, we need not to add prerequisites for each ruleset, whatever the rulesets listed in the stack will be considered as prerequisites and compile accordingly. Where as in RBV, each ruleset must have prerequisites list, otherwise it will not able to compile. For Ex: if Ruleset "A" is dependent on "B", B" is dependent on "C". These should be explicitly mentioned in each ruleset. Whereas for ABV no need to mention explicitly within ruleset, if the rulesets are as part of application stack.
One example which i have seen when we create an application from Wizard, generally 4 rule-sets are added in the stack 2 for app and 2 for org.
App level rule-sets are ABV whereas
Org level are RSV
and reason behind is we want to make sure the Org level rule-set have define pre-requisite attached like "Pega-ProcessCommander:07-10-99" and it can be any other rule-set as well to ensure every implementation level honor this w.r.t Org level structure across.
No, I don't think Org rulesets are RSV and App rulesets are ABV, Org rulesets also can have ABV. when we configure ABV, it will check the built on application for prerequisites, no need to add rule prerequisites explicitly. ABV reduces multiple references and configurations of prerequisites, if any prerequisite ruleset exists in application stack, it need not be explicitly configured for any other ruleset.