1. An enterprise resource planning system comprising: a processor, and an application, the application comprising: a plurality of business objects, a backend abstraction layer which comprises: a plurality of pre-coded interfaces for each business object, each interface including a rule identifying a condition on which the interface is to be used; and a plurality of pre-coded methods for each interface representing a complete set of read and write functions performed by the enterprise resource planning system on data stored at an external system to the enterprise resource planning system and used by a respective business object; a plurality of exit points associated with the pre-coded interfaces and the pre-coded methods; a connectivity layer which comprises: a plurality of customizable interfaces, each linked to a respective one of the pre-coded interfaces in the backend abstraction layer; a plurality of customizable operation fields in each of the customizable interfaces, each customizable operation field linked to a respective pre-coded method in a respective pre-coded interface, each customizable operation field storing third-party instructions recognized by the external system for performing the pre-coded read or write function specified by the respective linked pre-coded method at the external system; wherein the processor is operative to: execute the source code of the application; upon reaching one of the exit points, identify whether a condition in at least one pre-coded interface associated with the identified business object is met; when the condition is met, identify a pre-coded method in the identified interface associated with a selected function to be executed on the external system; and identify for transmission and execution at the external system the third-party instructions stored in a respective customizable operation field linked to the identified pre-coded method.