Summary: Causal Type System for Ambient Movements
Department of Computing and Information Sciences
Kansas State University
The Ambient Calculus was developed by Cardelli and Gordon as a formal framework to study issues
of mobility and migrant code. We present a type system for the calculus, parameterized by a set of
security constraints: static ones concerning where a given ambient may reside, and dynamic ones
expressing where a given ambient 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".
The type system employs a notion of causality in that processes are assigned "behaviors". We ar-
gue that 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 (in
contrast to other approaches) an ambient to hold multiple topics of conversation.
Based on techniques borrowed from finite automata theory, type checking of type-annotated pro-
cesses is decidable. Under certain quite natural restrictions, type inference is also possible.