  Processes are a crucial artefact in organizations, since they coordinate the
execution of activities so that products and services are provided. The use of
models to analyse the underlying processes is a well-known practice. However,
due to the complexity and continuous evolution of their processes,
organizations need an effective way of analysing the relation between processes
and models. Conformance checking techniques asses the suitability of a process
model in representing an underlying process, observed through a collection of
real executions. One important metric in conformance checking is to asses the
precision of the model with respect to the observed executions, i.e.,
characterize the ability of the model to produce behavior unrelated to the one
observed. In this paper we present the notion of anti-alignment as a concept to
help unveiling runs in the model that may deviate significantly from the
observed behavior. Using anti-alignments, a new metric for precision is
proposed. In contrast to existing metrics, anti-alignment based precision
metrics satisfy most of the required axioms highlighted in a recent
publication. Moreover, a complexity analysis of the problem of computing
anti-alignments is provided, which sheds light into the practicability of using
anti-alignment to estimate precision. Experiments are provided that witness the
validity of the concepts introduced in this paper.
