# A hierarchy of constraint systems for data-flow analysis of constraint logic-based languages

Many interesting analyses for constraint logic-based languages
are aimed at the detection of \emph{monotonic} properties, namely
of properties which are preserved as the computation progresses.
Our basic claim is that most, if not all, of these analyses can be
described within a unified notion of constraint domains.
We present a class of constraint systems which allows
for a smooth integration within an appropriate framework for the
definition of non-standard semantics of constraint logic-based languages.
Such a framework is also presented and motivated.
We then show how such domains can be built, as well as construction
techniques which induce a hierarchy of domains.
In particular, we propose a general methodology for domain combination
with asynchronous interaction (i.e.~the interaction is not necessarily
synchronized with the domains' operations).
Following this methodology, interesting combinations of domains
can be expressed with all the the semantic elegance
of concurrent constraint programming languages.