RQL: A Query Language for Recommender Systems

Initially popularized by Amazon.com, recommendation technologies have become widespread over the past several years, both in the industry and academia. The traditional two-dimensional approach to recommender systems, involving the dimensions of Users and Items, has been subsequently extended to the multidimensional approach supporting additional contextual dimensions and OLAP-type aggregation capabilities. Furthermore, the class of all possible recommendations available to the users in traditional recommender systems is typically determined by the vendor and is quite limited. In this paper we address this limitation by proposing a query language RQL that allows the users to formulate various types of recommendation requests on their own. RQL adapts OLAP queries to the domain of recommender systems and, therefore, is able to support both the traditional two-dimensional and the more complex multidimensional recommender systems. The paper also presents a recommendation algebra that allows mapping RQL queries into the algebraic expressions for the query processing purposes. Finally, the paper presents a method for executing RQL queries.