  Despite the large-scale uptake of semantic technologies in the biomedical
domain, little is known about common modelling practices in published
ontologies. OWL ontologies are often published only in the crude form of sets
of axioms leaving the underlying design opaque. However, a principled and
systematic ontology development life cycle is likely to be reflected in
regularities of the ontology's emergent syntactic structure. To develop an
understanding of this emergent structure, we propose to reverse-engineer
ontologies taking a syntax-directed approach for identifying and analysing
regularities for axioms and sets of axioms. We survey BioPortal in terms of
syntactic modelling trends and common practices for OWL axioms and class
frames. Our findings suggest that biomedical ontologies only share simple
syntactic structures in which OWL constructors are not deeply nested or
combined in a complex manner. While such simple structures often account for
large proportions of axioms in a given ontology, many ontologies also contain
non-trivial amounts of more complex syntactic structures that are not common
across ontologies.
