Bisimulations for Asynchronous Mobile Processes

Within the past few years there has been renewed interest in thestudy of value-passing process calculi as a consequence of the emergence of the pi-calculus. Here, [MPW89] have determined two variants of the notion of bisimulation, late and early bisimilarity. Most recently [San93] has proposed the new notion of open bisimulation equivalence. In this paper we consider Plain LAL, a mobile process calculus which differs from the pi-calculus in the sense that the communication of data values happens asynchronously. The surprising result is that in the presence of asynchrony, the open, late and early bisimulation equivalences coincide - this in contrast to the pi-calculus where they are distinct. The result allows us to formulate a common equational theory which is sound and complete for finite terms of Plain LAL

Migration = Cloning ; Aliasing (Preliminary Version)

In Obliq, a lexically scoped, distributed, object-based programming language, object migration was suggested as creating a (remote) copy of an object's state at the target site, followed by turning the (local) object itself into an alias, also called surrogate, for the just created remote copy. There is no proof that object migration in Obliq is safe in any sense. We consider the creation of object surrogates as an abstraction of the above-mentioned style of migration. We introduce Øjeblik, a distribution-free subset of Obliq, and provide two formal semantics, one in an intuitive configuration style, the other in terms of pi-calculus. The intuitive semantics shows why surrogation is neither safe in Obliq, nor can it be so in full generality in Repliq (a repaired Obliq). The pi-calculus semantics allows us to prove that surrogation in Øjeblik is safe for certain well-identified cases, thus suggesting that migration in Repliq may be safe, accordingly

Mobile Objects as Mobile Processes

Obliq is a lexically-scoped, distributed, object-based programming language. In Obliq, the migration of an object is proposed as creating a clone of the object at the target site, whereafter the original object is turned into an alias for the clone. Obliq has only an informal semantics, so there is no proof that this style of migration is safe i.e., transparent to object clients In previous work, we introduced Ojeblik, an abstraction of~Obliq, where, by lexical scoping sites have been abstracted away. We used Ojeblik in order to exhibit how the semantics behind Obliq's implementation renders migration unsafe. We also suggested a modified semantics that we conjectured instead to be safe. In this paper, we rewrite our modified semantics of \OBLIQ\ in terms of the pi-calculus, and we use it to formally prove the correctness of object surrogation, the abstraction of object migration in Ojebli

ALICE - ARC integration

AliEn or Alice Environment is the Grid middleware developed and used within the ALICE collaboration for storing and processing data in a distributed manner. ARC (Advanced Resource Connector) is the Grid middleware deployed across the Nordic countries and gluing together the resources within the Nordic Data Grid Facility (NDGF). In this paper we will present our approach to integrate AliEn and ARC, in the sense that ALICE data management and job processing can be carried out on the NDGF infrastructure, using the client tools available in AliEn. The inter-operation has two aspects, one is the data management part and the second the job management aspect. The first aspect was solved by using dCache across NDGF to handle data. Therefore, we will concentrate on the second part. Solving it, was somewhat cumbersome, mainly due to the different computing models employed by AliEn and ARC. AliEN uses an Agent based pull model while ARC handles jobs through the more 'traditional' push model. The solution comes as a module implementing the functionalities necessary to achieve AliEn job submission and management to ARC enabled sites

Grid Interoperation with ARC Middleware for the CMS Experiment

The Compact Muon Solenoid (CMS) is one of the general purpose experiments at the CERN Large Hadron Collider (LHC). CMS computing relies on different grid infrastructures to provide computational and storage resources. The major grid middleware stacks used for CMS computing are gLite, Open Science Grid (OSG) and ARC (Advanced Resource Connector). Helsinki Institute of Physics (HIP) hosts one of the Tier-2 centers for CMS computing. CMS Tier-2 centers operate software systems for data transfers (PhEDEx), Monte Carlo production (ProdAgent) and data analysis (CRAB). In order to provide the Tier-2 services for CMS, HIP uses tools and components from both ARC and gLite grid middleware stacks. Interoperation between grid systems is a challenging problem and HIP uses two different solutions to provide the needed services. The first solution is based on gLite-ARC grid level interoperability. This allows to use ARC resources in CMS without modifying the CMS application software. The second solution is based on developing specific ARC plugins in CMS software

This document in subdirectoryRS/98/52/ Imperative Objects and Mobile Processes

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