In computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, the ambient calculus is a process calculus

Process calculus

In computer science, the process calculi are a diverse family of related approaches for formally modelling concurrent systems. Process calculi provide a tool for the high-level description of interactions, communications, and synchronizations between a collection of independent agents or processes...

 devised by Luca Cardelli

Luca Cardelli

Luca Cardelli is an Italian computer scientist who is currently an Assistant Director at Microsoft Research in Cambridge, UK. Cardelli is well-known for his research in type theory and operational semantics. Among other contributions he implemented the first compiler for the functional programming...

 and Andrew D. Gordon

Andrew D. Gordon

Andrew D. Gordon is a British computer scientist.Gordon is the co-designer of Spi Calculus , Ambient calculus , and...

 in 1998, and used to describe and theorise about concurrent systems that include mobility. Here mobility means both computation carried out on mobile devices (i.e. networks that have a dynamic topology), and mobile computation (i.e. executable code that is able to move around the network). The ambient calculus provides a unified framework for modeling both kinds of mobility. It is used to model interactions in such concurrent systems as the Internet

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

.

Since its inception, the ambient calculus has grown into a family of closely related ambient calculi.

Ambients

The fundamental primitive of the ambient calculus is the ambient. An ambient is informally defined as a bounded place in which computation can occur. The notion of boundaries is considered key to representing mobility, since a boundary defines a contained computational agent that can be moved in its entirety. Examples of ambients include:

• a web page (bounded by a file)
• a virtual address space (bounded by an addressing range)
• a Unix file system (bounded within a physical volume)
• a single data object (bounded by “self
  This (computer science)
  In many object-oriented programming languages, this is a keyword that is used in instance methods to refer to the object on which they are working. C++ and languages which derive in style from it generally use this...
  
  ”)
• a laptop (bounded by its case and data ports)

The key properties of ambients within the Ambient calculus are:

• Ambients have names, which are used to control access to the ambient
• Ambients can be nested inside other ambients (representing, for example, administrative domains)
• Ambients can be moved as a whole

Operations

Computation is represented as the crossing of boundaries, i.e. the movement of ambients. There are three basic operations (or capabilities) on ambients:

• instructs the surrounding ambient to enter some sibling ambient , and then proceed as
• instructs the surrounding ambient to exit its parent ambient
• instructs the surrounding ambient to dissolve the boundary of an ambient located at the same level
• makes any number of copy of something

The Ambient calculus provides a reduction semantics that formally defines what the results of these operations are.

Communication within (i.e. local to) an ambient is anonymous and asynchronous. Output actions release names or capabilities into the surrounding ambient. Input actions capture a value from the ambient, and bind it to a variable. Non-local I/O can be represented in terms of these local communications actions by a variety of means. One approach is to use mobile “messenger” agents that carry a message from one ambient to another (using the capabilities described above). Another approach is to emulate channel-based communications by modeling a channel in terms of ambients and operations on those ambients. The three basic ambient primitives, namely in, out, and open are expressive enough to simulate name-passing channels in the π-calculus

Pi-calculus

In theoretical computer science, the π-calculus is a process calculus originally developed by Robin Milner, and David Walker as a continuation of work on the process calculus CCS...

.

External links

• Mobile Computational Ambients by Luca Cardelli
  Luca Cardelli
  Luca Cardelli is an Italian computer scientist who is currently an Assistant Director at Microsoft Research in Cambridge, UK. Cardelli is well-known for his research in type theory and operational semantics. Among other contributions he implemented the first compiler for the functional programming...