Context: The Unified Modeling Language (UML), with its 14
different diagram types, is the de-facto standard tool for objectoriented
modeling and documentation. Since the various UML
diagrams describe different aspects of one, and only one, software
under development, they are not independent but strongly depend
on each other in many ways. In other words, the UML diagrams
describing a software must be consistent. Inconsistencies between
these diagrams may be a source of the considerable increase of
faults in software systems. It is therefore paramount that these
inconsistencies be detected, analyzed and hopefully fixed.

Objective:
The aim of this article is to deliver a comprehensive
summary of UML consistency rules as they are described in the
literature to date to obtain an extensive and detailed overview of
the current research in this area.

Method:
We performed a Systematic Mapping Study by
following well-known guidelines. We selected 94 primary studies
from a search with seven search engines performed in December
2012.

Results:
Different results are worth mentioning. First it appears
that researchers tend to discuss very similar consistency rules,
over and over again. Most rules are horizontal (98.07%) and
syntactic (88.03%). The most used diagrams are the class diagram
(71.28%), the state machine diagram (42.55%) and the sequence
diagram (47.87%).

Conclusion:
The fact that many rules are duplicated in primary
studies confirms the need for a well accepted list of consistency
rules. This paper is a first step in this direction. Results indicate
that much more work is needed to develop consistency rules for
all 14 UML diagrams, in all dimensions of consistency (e.g.,
semantic and syntactic on the one hand, horizontal, vertical and
evolution on the other hand).