  Existential rules are an expressive knowledge representation language mainly
developed to query data. In the literature, they are often supposed to be in
some normal form that simplifies technical developments. For instance, a common
assumption is that rule heads are atomic, i.e., restricted to a single atom.
Such assumptions are considered to be made without loss of generality as long
as all sets of rules can be normalised while preserving entailment. However, an
important question is whether the properties that ensure the decidability of
reasoning are preserved as well. We provide a systematic study of the impact of
these procedures on the different chase variants with respect to chase
(non-)termination and FO-rewritability. This also leads us to study open
problems related to chase termination of independent interest.
