“A functional theory does not necessarily translate into a successful practice”.

Jonathan Zittrain

716. PREFACE – For more than 20 years, the controller-processor model has provided the analytical template for the allocation of responsibility and liability among actors involved in the processing of personal data. While the model itself appears conceptually sound, its application in practice has not always been straightforward. The research objective of this Part of the book is to identify the main issues that surround the practical application of the controller-processor model. To this end, a number of real-life use cases will be examined.

717. SELECTION CRITERIA – Needless to say, it is impossible to document and analyse every possible use case. A selection needs to be made. In social science research, case selection is generally driven by two objectives, namely (1) representativeness (i.e. ensuring that the selected cases are sufficiently representative in light of the research question) and (2) variety (i.e. ensuring useful variation on the dimensions of theoretical interest). A third, sometimes implicit, objective is relevancy (i.e. ensuring that the selected use cases are likely to yield insights which can assist in answering the research question).

718. RELEVANCY – As the research objective of this Part of the book is to document the issues that arise when applying the controller-processor model in practice, the pool of potentially relevant use cases is limited to instances in which such issues occur. In the first phase of selection, a preliminary literature study was undertaken to identify eligible use cases. The threshold for eligibility was the existence of some indication, either in regulatory guidance or doctrine, that the use case in question challenges either the application of the controller and processor concepts or the associated allocation of responsibility and liability. Each of the retained use cases has been cited by scholars and/or regulators as instances where the application of the controller-processor concepts can be challenging, or where the effective allocation of responsibilities and liability may be undermined.

719. VARIETY – Once the initial screening for relevancy was completed, a further selection was made with the aim of ensuring a sufficient degree of variety. In practice, the control capabilities of actors involved in the processing of personal data are shaped by the social context in which they operate (e.g. public sector, business-to-business, business-to-consumer, consumer-to-consumer).