  Categorization is one of the basic tasks in machine learning and data
analysis. Building on formal concept analysis (FCA), the starting point of the
present work is that different ways to categorize a given set of objects exist,
which depend on the choice of the sets of features used to classify them, and
different such sets of features may yield better or worse categorizations,
relative to the task at hand. In their turn, the (a priori) choice of a
particular set of features over another might be subjective and express a
certain epistemic stance (e.g. interests, relevance, preferences) of an agent
or a group of agents, namely, their interrogative agenda. In the present paper,
we represent interrogative agendas as sets of features, and explore and compare
different ways to categorize objects w.r.t. different sets of features
(agendas). We first develop a simple unsupervised FCA-based algorithm for
outlier detection which uses categorizations arising from different agendas. We
then present a supervised meta-learning algorithm to learn suitable (fuzzy)
agendas for categorization as sets of features with different weights or
masses. We combine this meta-learning algorithm with the unsupervised outlier
detection algorithm to obtain a supervised outlier detection algorithm. We show
that these algorithms perform at par with commonly used algorithms for outlier
detection on commonly used datasets in outlier detection. These algorithms
provide both local and global explanations of their results.
