1. A method comprising: at an application platform system that includes a first application system, a second application system, and a multi-tenant data synchronization system (DSS): the DSS configuring a first data synchronization instance for a first account of the DSS, responsive to a request provided by a system of the first account, wherein the first data synchronization instance manages a first reference state representation object for the first account at the DSS; the first application system storing a first local state representation object that corresponds to the first reference state representation object of the DSS, wherein the first application system is constructed to receive first reference state representation object update notifications provided by the DSS; the second application system storing a second local state representation object that corresponds to the first reference state representation object of the DSS, wherein the second application system is constructed to receive first reference state representation object update notifications provided by the DSS; the first application system transforming a first application instruction of the first application system into a first state update, and modifying the first local state representation object to include the first state update; the first application system providing at least the first state update of the modified first local state representation object to the DSS via a first local state representation object update notification; responsive to the first state update, the DSS determining whether to modify the first reference state representation object of the DSS to include the first state update; responsive to a determination by the DSS to modify the first reference state representation object to include the first state update, the DSS modifying the first reference state representation object to include the first state update, the DSS providing at least the first state update to the second application system via a first reference state representation object update notification; responsive to the first state update, the second application system modifying the second local state representation object to include the first state update, wherein the first application system and the second application system communicate by using the DSS.