Rewriting logic has been proposed as a unified model of parallel and concurrent computation, especially concurrent object-oriented computation and agent oriented computation. In this paper, we present a category-theoretic technique in which simulation relation between concurrent processes described by rewriting logic is analyzed. In this technique, simulation relation is represented by morphisms in the category of concurrent processes. Moreover, this technique is shown to be applicable to Petri nets by modeling them by rewriting logic. By this method, it is acknowledged that our technique is applicable to Petri nets including multi-loops whose treatment is limited in other techniques.

This paper describes MENDELS ZONE, a Petri-net-based concurrent programming environment, which is especially suitable for cooperating discrete event systems. MENDELS ZONE adopts MENDEL net, which is a type of high level (hierarchical colored) Petri net. One of the characteristics of the MENDEL nets is a process-oriented hierarchy like CCS, which is different from the subnet-oriented hierarchy in the Jensen's hierarchical colored Petri net. In a process-oriented hierarchy, a hierarchical unit is a process, which is more natural for cooperating and decentralized discrete event control systems. This paper also proposes a design methodology for MENDEL nets. Although many Petri net tools have been proposed, most tools support only drawing, simulation, and analysis of Petri nets; few tools support the design methodology for Petri nets. While Petri nets are good final design documents easy to understand, analyzable, and executable it is often difficult to write Petri nets directly in an earlier design phase when the system structure is obscure. A proposed design methodology makes a designer to construct MENDEL nets systematically using causality matrices and temporal logic. Furthemore, constructed MENDEL nets can be automatically compiled into a concurrent programming language and executed on a parallel computer.

We propose a programming language, Flage, for building software systems which dynamically adapt to changing local situations. In our language, we construct applications by agents; concurrent mobile objects with the metalevel architecture. Metalevel programming facilities realize a self-control of an agent's actions and an autonomous adaptation to changes. We also introduce another kind of program element called field. A field represents a local situation around agents. For example, one field represents a virtual place to get local information in a network environment and another represents a virtual place where agents do cooperative works. If an agent enters a field, it gets programs and shared information in the field. By moving field to field, an agent can change its program composition by itself and it adapts to changing local situations. In this paper, we describe the language specification of Flage, the implementation of the platform for Flage programming and show some program examples.

Live migration plays an important role on improving efficiency of cloud data centers by enabling dynamically replacing virtual machines (VMs) without disrupting services running on them. Although many studies have proposed acceleration mechanisms of live migration, IO-intensive VMs still suffer from long total migration time due to a large amount of page cache. Existing studies for this problem either force the guest OS to delete the page cache before a migration, or they do not consider dynamic characteristics of cloud data centers. We propose a parallel and adaptive transfer of page cache for migrating IO-intensive VMs which (1) does not delete the page cache and is still fast by utilizing the storage area network of a data center, and (2) achieves the shortest total migration time without tuning hand-crafted parameters. Experiments showed that our method reduces total migration time of IO-intensive VMs up to 33.9%.

This paper describes the architecture to implement an application in network environments, which adapts to unexpected change in the development phase. In this architecture, an application is expressed as an agent which consists of two layers: base level and meta level. The base level program is an application program and the meta level program is the program that controls the execution of the base level and changes the base level program. Virtual places are also provided in the network. They are used for the release of programs and information which agents retrieve to change their own base level program. An application (or an agent), when a change is required, moves from places to places for the retrieval of programs to adapt to the change. A program search strategy is introduced to adapt to changes by using distributed thesauri of released programs, which realizes an agent's program retrieval method in network environments.

Refinement-based formal specification is a promising approach to the increasing complexity of software systems, as demonstrated in the formal method Event-B. It allows stepwise modeling and verifying of complex systems with multiple steps at different abstraction levels. However, making changes is more difficult, as caution is necessary to avoid breaking the consistency between the steps. Judging whether a change is valid or not is a non-trivial task, as the logical dependency relationships between the modeling elements (predicates) are implicit and complex. In this paper, we propose a method for analyzing the impact of the changes of Event-B. By attaching labels to modeling elements (predicates), the method helps engineers understand how a model is structured and what needs to be modified to accomplish a change.

Net-Oriented Analysis and Design (NOAD) is defined as three items: (1) Various nets are utilized as an effective modeling method. (2) Inter-relationships among verious nets are determined. (3) Verification or analysis methods for nets are provided and they are implemented based on the mathematical theory, that is Net theory. Very few methods have been presented to satisfy these three items. For example, the Real-Time SA method covers item (1) only. The Object-Oriented Analysis and Design method (OOA/OOD) covers items (1) and (2). NOAD can be regarded as an extension to OOA/OOD. This paper discusses how effectively various nets have been used in actual software development support metnods and tools and evaluates such several methods and tools from the NOAD viewpoint.

Interoperability between different systems is becoming a more important issue for open distributed systems. In this paper, we investigate what kind of framework we need for constructing open distributed systems. Firstly, we enumerate the features and functions which the framework should have. We then evaluate a proposed multi-agent framework, Bee-gent, by using a typical example of open distributed systems. Lastly, we show clearly what is required for such a framework.

As a variety of digital services are provided through networks, more and more efforts are made to ensure dependability of software behavior implementing services. Formal methods and tools have been considered as promising means to support dependability in complex software systems during the development. On the other hand, there have been serious doubts on practical applicability of formal methods. This paper overviews the present state of formal methods and discusses their applicability, especially focusing on two representative methods (SPIN and B Method) and their recent industrial applications. This paper also discusses applications of formal methods to dependable networked software.

Both Petri nets and temporal logic have been widely used to specify concurrent programs. Petri nets appropriate to specify the behavioral structures of programs explicitly, while temporal logic is appropriate to specify the properties and constraints of programs. Since one can complement the other, using a combination of Petri nets and temporal logic is a highly promising approach to analyze, verify and synthesize concurrent programs. For the purpose of automatic program verification and synthesis, the emptiness problem (i.e., wheter a legal firing transition sequence satisfying a given temporal logic formula on a given Petri net exists) must be decidable. This paper reports a class to combine Petri nets and temporal logic as an infinite language and whose emptiness problem is decidable. We then show how to verify concurrent programs, using Petri nets and temporal logic, and also propose a compositional synthesis method that tune up reusable program components to satisfy a temporal logic specification.

Systems comprised of multiple interacting mobile agents provide an alternate network computing paradigm that integrates remote data access, message exchange and migration; which up until now have largely been considered independently. On the surface distributed systems design could be helped by a complete specification of the different interaction patterns, however the number of possible designs in any large scale system undergoes a combinatorial explosion. As a consequence this paper focuses on basic one-to-one agent interactions, or paradigms, which can be used as building blocks; allowing larger system characteristics and performance to be understood in terms of their combination. This paper defines three basic agent paradigms and presents associated performance models. The paradigms are evaluated quantitatively in terms of network traffic, overall processing time and size of memory used, in the context of a distributed DB system developed using the Bee-gent Agent Framework. Comparison of the results and models illustrates the performance trade-off for each paradigm, which are not represented in the models, and some implementation issues of agent frameworks. The paper ends with a case study of how to select an appropriate paradigm.

This paper concerns a Petri-net-based model for describing reactive and concurrent systems. Although many high-level Petri nets have been proposed, they are insufficiently practical to describe reactive and concurrent systems in the detail modeling, design and implementation phases. They are mainly intended to describe concurrent systems in the rough modeling phase and lack in several important features (e.g., concurrent tasks, task communication/synchronization, I/O interface, task scheduling) which the most actual implementations of reactive and concurrent systems have. Therefore it is impossible to simulate and analyze the systems accurately without explicitly modeling these features. On the other hand, programming languages based on Petri nets are deeply dependent on their execution environments and not sophisticated as modeling and specification languages. This paper proposes MENDEL net which is a high-level Petri net extended by incorporating concurrent tasks, task communication/synchronization, I/O interface, and task scheduling in a sophisticated manner. MENDEL nets are a wide-spectrum modeling language, that is, they are suitable for not only modeling but also designing and implementing reactive and concurrent systems.

Recommender System (RS) predicts user's ratings towards items, and then recommends highly-predicted items to user. In recent years, RS has been playing more and more important role in the agent research field. There have been a great deal of researches trying to apply agent technology to RS. Collaborative Filtering, one of the most widely used approach to predict user's ratings in Recommender System, predicts a user's rating towards an item by aggregating ratings given by users who have similar preference to that user. In existing approaches, user similarity is often computed on the whole set of items. However, because the number of items is often very large and so is the diversity among items, users who have similar preference in one category may have totally different judgement on items of another kind. In order to deal with this problem, we propose a method to cluster items, so that inside a cluster, similarity between users does not change significantly from item to item. After the item clustering phase, when predicting rating of a user towards an item, we only aggregate ratings of users who have similarity preference to that user inside the cluster of that item. Experiments evaluating our approach are carried out on the real dataset taken from MovieLens, a movies recommendation web site. Experiment results suggest that our approach can improve prediction accuracy compared to existing approaches.