Recent research suggests that users of a recommender system may like to receive useful unexpected suggestions that provide a pleasant surprise. This concept, called serendipity, is one of the aspects that have been proposed to meet user expectations for the recommendations they receive. Introducing serendipity means going beyond the “more of the same” aspect that past recommender systems are criticized for. A new approach has recently been proposed to create user models from their previous ratings. In this paper, we show how this user modelling approach can be used to investigate the relationship between users’ preferences, their previous ratings and their judgments related to serendipity. Experiments in the movie domain show that the more relevant an item is to a user, the more willing the user is to discover attributes that are unfamiliar to him, as long as these attributes do not play an important role in his ratings.

Recommender systems offer recommendations based on user's previous ratings. However, sometimes the user is interested in unusual and interesting items that do not exactly match her user profile, as defined by the system. Serendipity, a concept that can be interpreted primarily as surprise, is one of the "beyond-accuracy" aspects that have been proposed to be considered to meet user's expectations for the recommendations she/he gets. Although recent studies attempt to address the serendipity problem, there is still a variety of interpretations regarding the definition, the measurement and the application of serendipity in recommender systems. Our proposed method follows the distance-based approach for multi-dimensional serendipity measurement, which refers to the expected items for the user as a benchmark for measuring serendipity. For integrating serendipity into recommendations, we propose a novel serendipity-oriented user modeling method, based on graph-theory approach - resolving sets in a graph, which enables finding serendipitous items in a multi-dimensional content-based space by detecting the expected items for the user.