Summary: Causal Type System for Ambient Movements
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 type-annotated 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 "co-capabilities" (an otherwise
increasingly popular extension to the ambient calculus); also it allows an
ambient to hold multiple topics of conversation.