1. A method for implementing a persistence application programming interface (API) that is platform independent and can make up-calls to business logic, the method comprising: receiving a request at the API to execute a command at a persistence tier of an n-tier distributed application; in response to the request, determining an entity type for an entity affected by the command; identifying a function at a middle tier of the n-tier distributed application that is associated with the entity type and the command, wherein the middle tier includes the business logic; sending an instruction from the API at the persistence tier to the middle tier to execute the function, wherein the instruction specifies the function, and wherein the function already exists at the middle tier, whereby the persistence tier is directing the execution of the function at the middle tier by making an up-call to the middle tier; and upon receiving a confirmation at the API that the function executed, executing the command at the persistence tier.