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We develop a semantics theory for SAP, a variant of Levi and Sangiorgi's Safe Ambients, SA. The dynamics of SA relies upon capabilities (and co-capabilities) exercised by mobile agents, called ambients, to interact with each other. These capabilities contain references, the names of ambients with which they wish to interact. In SAP we generalize the notion of capability: in order to interact with an ambient n, an ambient m must exercise a capability indicating both n and a password h to access n; the interaction between n and m takes place only if n is willing to perform a corresponding co-capability with the same password h. The name h can also be looked upon as a port to access ambient n via port h. In SAP, by managing passwords/ports, for example generating new ones and distributing them selectively, an ambient may now program who may migrate into its computation space, and when. Moreover in SAP, an ambient may provide different services/resources depending on the port accessed by the incoming clients. Then we give an Its-based operational semantics for SAP and a labelled bisimulation equivalence, which is proved to coincide with reduction barbed congruence. We use our notion of bisimulation to prove a set of algebraic laws that are subsequently exploited to prove more significant examples. [ABSTRACT FROM AUTHOR]

Over the past years, mobile agent technology has attracted considerable attention, and a significant body of literature has been published. To further develop mobile agent technology, reliability mechanisms such as fault tolerance and transaction support are required. This article aims at structuring the field of fault-tolerant and transactional mobile agent execution and thus at guiding the reader to understand the basic strengths and weaknesses of existing approaches. It starts with a discussion on providing fault tolerance in a system in which processes simply fail. For this purpose, we first identify two basic requirements for fault-tolerant mobile agent execution: (1) non-blocking (i.e., a single failure does not prevent progress of the mobile agent execution) and (2) exactly-once (i.e., multiple executions of the agent are prevented). This leads us to introduce the notion of a local transaction as the basic building block for fault-tolerant mobile agent execution and to classify existing approaches according to when and by whom the local transactions are committed. In a second part, we show that transactional mobile agent execution additionally ensures execution atomicity and present a survey of existing approaches. In the last part of the survey, we extend the notion of fault tolerance to arbitrary Byzantine failures and security-related issues of the mobile agent execution. [ABSTRACT FROM AUTHOR]