Software Defined Networking (SDN) aims to help overcome the complexities inherent in traditional networks. The main concept in SDN is the decoupling of the data layer from the control layer, the latter of which is centralised in a controller. OpenFlow has been adopted as the standard protocol for the southbound interface, where the controller communicates with forwarding devices. However, the northbound interface (NBI), connecting the controller with end-user business applications, does not have an open standard. NBIs have accelerated application development because developers can implement required functionality without the need to consider matters related to the data layer, but there is an issue of compatibility because each SDN has its own NBI. In this position paper we present a plan to design a RESTful NBI for SDN applications to improve compatibility across SDN technologies.