This paper presents a novel approach for the elaboration of an integration strategy for controls and computing systems at large particle accelerator based research facilities. The approach is applied in a specific case study conducted at the world-leading neutron science facility European Spallation Source (ESS). First, an introduction to the term `integration' in the Systems Engineering literature is presented. Also, the common integration practices and challenges in the domain of controls and computing systems for particle accelerators are described. An approach for the elaboration of an integration strategy is proposed. It is based on the information needs for successful integration in this domain. The approach has been applied to a case study and the first preliminary results are shown. Systems-of-systems (SoS) characteristics of the case study are outlined. A discussion and evaluation of the result from the case study and the applied research methodology conclude the paper.