Summary: Causal Type System for Ambient Movements #
Torben Amtoft ##
Abstract. The Ambient Calculus was developed by Cardelli and Gor
don as a formal framework to study issues of mobility and migrant code.
We present a type system for the calculus, parameterized by security con
straints expressing where a given ambient may reside and where it may
be dissolved. A subject reduction property then guarantees that a well
typed process never violates these constraints; additionally it ensures
that communicating subprocesses agree on their ``topic of conversation''.
Based on techniques borrowed from finite automata theory, type check
ing of typeannotated processes is decidable. Under certain quite natural
restrictions, type inference is also possible.
The type system employs a notion of causality in that processes are
assigned ``behaviors''. This significantly increases the precision of the
analysis and compensates for the lack of ``cocapabilities'' (an otherwise
increasingly popular extension to the ambient calculus); also it allows an
ambient to hold multiple topics of conversation.