Declare Index rules are not in the Decision category because
Like all four other declarative rule types, Rule-Declare-Index rules execute automatically as soon as they are created.
And like all four other declarative rule types, individual Rule-Declare-Index rules are not explicitly referenced by any other rules. They quietly carry out their assigned mission bidding, automatically and as-required.
Unlike the other four declarative rule types, Rule-Declare-Index rules are part of the SysAdmin category. That's because they function similar to database views, a concept that system administrators may already understand.
Index rules automatically add and delete instances of a concrete class derived from the Index- base class. For example, the standard Rule-Declare-Index rule named Work-.PartyURI writes out instances of Index-WorkPartyURI that support searches by party. On the Process Work panel, the Search for Work Associated with me by party function uses these index instances to rapidly fetch those that reference me as the Originator or Customer or another party.
Suresh 2018/04/20 Case Management