Mobile Agent Coordination for Distributed Network Management

Mobile agents are a promising technology to face the problems raised by the increasing complexity and size of today's networks. In particular, in the area of network management, mobile agents can lead to a fully distributed paradigm to overcome the limits of traditional centralized approaches. A basic requirement for the management of a complex network is the definition of high-level and flexible models to coordinate the accesses to the resources—data and services—provided by the network nodes. On this basis, this paper describes the MARS coordination architecture for mobile agents. MARS is based on the definition of programmable tuple spaces associated with the network nodes: mobile agents can access the local resources and services via the tuple space, thus adopting a standard and high-level interface. The network administrator—via mobile agents—can dynamically program the behavior of the tuple space in reaction to the agents' access to the tuple space, thus leading to a flexible network model. Several examples show the effectiveness of the MARS approach in supporting network management activities.     

Design and Implementation of a Hybrid Agent Platform

This paper presents IMAP, a hybrid agent platform composed of several cooperating intelligent agents and mobile agents. IMAP is implemented in Java and Prolog. Java is used to implement the framework of the system, and in particular for supporting the communication between agents and mobility of agent, while Prolog is used to implement both adduction and derivation mechanisms. IMAP intends to independently employ the underlying derivation/adduction and mobility mechanism. In IMAP, intelligent agent and mobile agent can not only fully exploit individual virtue, but also cooperate to perform a task under a uniform platform. Intelligent agents in IMAP are equipped with hypothetical reasoning capabilities, performed by means of adduction: if the knowledge available to an agent is insufficient to solve a query, the agent could adduce new hypotheses. Each intelligent agent can accept queries from mobile agents by means of the interface module, each query is passed to the reasoning module of intelligent agent which performs a derivation and adduction in order to get an answer for mobile agent. IMAP also provides mobile agents a flexible and efficient coordination mechanism and a reliable migration mechanism, and supports persistence of agent state and agent security. Mobile agent's coordination mechanism exploits the advantages of the XML language and Linda-like coordination. This programmable Linda-like coordination mechanism suits the mobility and openness of the Internet application, XML standard for Internet data representation may guarantee a high-degree of interoperability between heterogeneous environments. The design and implementation key technologies of IMAP are described in this paper. An Internet based auction application example shows the suitability and the effectiveness of the IMAP, and its performance evaluation is also made. Finally, some conclusions and remarks are given.     

移动代理应用中上下文相关的客观协调

移动代理之间需要进行交互合作才能完成系统任务,每个移动代理也需要与它运行所在的移动代理环境进行交互。文章提出了一种在移动代理应用系统中的上下文相关的客观协调模型,适合移动代理系统中移动代理之间的交互和移动代理与移动代理环境之间的交互,它把全局的耦合交互转变成本地独立的元组空间交互,用可编程的元组空间解决由代理移动引起的上下文相关协调问题,而且环境相关的协调策略和应用相关的协调策略可以集成到可编程的元组空间中。     

Agents for information retrieval: Issues of mobility and coordination

This paper focuses on agent-based applications for information retrieval on the Web, by specifically analysing mobility and coordination issues. On the one hand, mobile agents well suit the requirements of information retrieval in the new dynamic scenario derived from the Internet. This is due to their capability of moving to the place where the information is stored – therefore saving bandwidth – and to their robustness in the presence of unreliable connections. On the other hand, the search for information by several mobile active agents calls for suitable models to rule the interactions among agents and between agents and execution environments. The paper surveys different coordination approaches and evaluates their impact in information retrieval applications based on mobile agents. The survey outlines the advantages of uncoupled coordination models and points out the suitability of a coordination model based on reactive and programmable tuple spaces: they may increase the safety and the security of the environment while simplifying the task of programming distributed mobile agent applications.     

A mobile agent platform based on tuple space coordination

This paper presents JMAP, a Java-based mobile agents platform. JMAP provides a flexible and efficient agent coordination mechanism and a reliable agent migration mechanism, and supports persistence of agent state and agent security. The unique feature of JMAP is its agent coordination mechanism that exploits the advantages of the extensible markup language (XML) and Linda-like coordination. This XML-based Linda-like coordination mechanism suits the mobility and openness of the Internet application. The XML standard for Internet data representation can guarantee a high degree of interoperability between heterogeneous environments. The design and implementation of key technologies of JMAP are described in this paper. An agent-based application example shows the suitability and the effectiveness of the JMAP. Performance evaluation is made and comparisons with other mobile agent platforms are also made. Meanwhile, some related works are discussed. Finally, some conclusions and remarks are given.     

Experiences of Using Generative Communications to Support Adaptive Mobile Applications

Attention has recently begun to focus on the use of asynchronous paradigms to support adaptive mobile applications. To investigate this issue the authors have developed an asynchronous distributed systems platform based on the tuple space paradigm [19] coupled with extensions to support operation in mobile environments. This paper presents our experiences of developing and using this platform. The benefits of the tuple space approach are highlighted and we discuss in some detail the design, implementation and performance of our platform. We subsequently focus on the critical issues of the tuple space API and the level of support for adaptation which can be provided without compromising the elegance and simplicity of the paradigm. The paper concludes with an analysis of the suitability of platforms based on the tuple space paradigm for use in mobile environments.     

Coordination for Internet Application Development

The adoption of a powerful and expressive coordination model represents a key-point for the effective design and development of Internet applications. In this paper, we present the TuCSoN coordination model for Internet applications based on network-aware and mobile agents, and show how the adoption of TuCSoN can positively benefit the design and development of such applications, firstly in general terms, then via a TuCSoN-coordinated sample application. This is achieved by providing for an Internet interaction space made up of a multiplicity of independently programmable communication abstractions, called tuple centres, whose behaviour can be defined so as to embody the laws of coordination.     

Implementation of the XML linking language XLink by functional methods

This paper is devoted to the construction of processors of a language for describing links between resources in XML documents, which is based on the application of functional programming methods and representation of XML data as S-expressions. An implementation in the high-level functional programming language Scheme, the system SXLink compatible with the XLink specification of the W3 consortium, is considered. A survey and comparative analysis of the existing implementations of the XLink language are given. Typical difficulties associated with the implementation and use of the language are identified, and methods to overcome them are discussed. Examples of the application of the SXLink system to solving problems of processing links between resources in XML documents are considered. An SXLink application program interface based on the use of functions of the Scheme language as first-class objects is suggested. The application of this approach to constructing simple and powerful XLink processors is discussed.Translated from Programmirovanie, Vol. 31, No. 1, 2005. Original Russian Text Copyright © 2005 by Lizorkin, Lisovsky.     

On utilizing variables for specifying FDs in data-centric XML documents

We are interested in specifying functional dependencies (FDs) for data-centric XML documents (XML documents that are used mainly for data storage). FDs are a natural constraint. Specifying FDs for XML documents is more difficult because unlike relational databases, XML documents do not have uniform structures. This paper introduces XML Template Functional Dependencies (XTFDs), which are able to specify FDs for XML documents. This paper also presents a necessary and sufficient condition for an XTFD to cause data redundancy in XML documents. Further, we propose Attribute Rule and Text String Rule as two procedures that can be repeatedly applied to remove redundancy caused by XTFDs. In addition, we prove that if an XML document has data redundancy with respect to an FD specified by using the tree tuple approach, it would have data redundancy with respect to an XTFD and show by example that XTFDs can specify some FDs for XML documents that the tree tuple approach cannot.     

KLAIM: a kernel language for agents interaction and mobility

We investigate the issue of designing a kernel programming language for mobile computing and describe KLAIM, a language that supports a programming paradigm where processes, like data, can be moved from one computing environment to another. The language consists of a core Linda with multiple tuple spaces and of a set of operators for building processes. KLAIM naturally supports programming with explicit localities. Localities are first-class data (they can be manipulated like any other data), but the language provides coordination mechanisms to control the interaction protocols among located processes. The formal operational semantics is useful for discussing the design of the language and provides guidelines for implementations. KLAIM is equipped with a type system that statically checks access right violations of mobile agents. Types are used to describe the intentions (read, write, execute, etc.) of processes in relation to the various localities. The type system is used to determine the operations that processes want to perform at each locality, and to check whether they comply with the declared intentions and whether they have the necessary rights to perform the intended operations at the specific localities. Via a series of examples, we show that many mobile code programming paradigms can be naturally implemented in our kernel language. We also present a prototype implementation of KLAIM in Java     

Xml dataspaces for the coordination of internet agents

This article presents MARS-X, a programmable coordination architecture for autonomous and mobile Internet agents. In MARS-X, mobile Internet agents coordinate through programmable XML dataspaces, accessed by agents in a Linda-like fashion. Therefore, MARS-X enforces open and uncoupled interactions and, via XML, it offers a high degree of standard interoperability. These properties suit very well the characteristics of both mobile Internet agents and the Internet environment itself. In addition, coordination in MARS-X is made more flexible and secure by the capability of programming the behavior of the XML dataspaces by reaction to the agents' accesses. An application example related to the management of on-line academic courses shows the suitability and effectiveness of the MARS-X architecture.     

XMLNET: An Architecture for Cost Effective Network Management Based on XML Technologies

XML technologies have been recently introduced in network management towards alleviating limitations of SNMP. The XML W3C standard, along with XML technologies has the potential to boost open, interoperable, cost-effective and standards-based management solutions. This paper highlights recent efforts towards XML network management and introduces an architecture supporting XML-based network management applications. This architecture specifies a runtime environment that parses XML documents containing composite operations for individual devices, as well as for heterogeneous mutli-vendor networks. Management operations in the scope of XML documents are defined in a programmable fashion based on an XML-based composition language supporting aggregations of elementary operations, looping commands, conditional statements, as well as simple rules signifying the occurrence of specific events. The introduced environment allows network managers to define management operations featuring high-level semantics and accordingly produce sophisticated applications through XML authoring. Following the illustration of the architecture, its composition language and issues relating to security and error handling, the paper ends up presenting a prototype implementation, along with associated performance evaluation results.

Engineering mobile agent applications via context-dependent coordination

The design and development of Internet applications requiring dynamic and possibly mobile access to Internet resources can take advantage of an approach based on autonomous mobile agents. However, mobility introduces peculiar issues related to the modeling and management of the agents' coordination activities. This paper introduces context-dependent coordination as a framework for the design and development of Internet applications based on mobile agents, and shows how it can be supported by a proper coordination infrastructure. Context-dependent coordination is centered on the notion of programmable coordination media, as the software abstraction via which an agent in an Internet site can access to local resources and coordinate with local agents. Programmability stems from the fact that the behavior of the media can be fully configured to influence agents' coordination activities. This enables local administrators to configure coordination media so as to enact site-dependent coordination policies, and mobile agents to configure the accessed coordination media to obtain an application-dependent behavior of the media themselves. Several application examples shows that exploiting context-dependent coordination promotes a clear separation of concerns in design and development, and can make applications more modular and easier to be maintained. The MARS system is assumed as an exemplar coordination infrastructure to clarify the concepts expressed and to show their actual implementation.     

Extending type systems in a library: Type-safe XML processing in C++

Type systems built directly into the compiler or interpreter of a programming language cannot be easily extended to keep track of run-time invariants of new abstractions. Yet, programming with domain-specific abstractions could benefit from additional static checking. This paper presents library techniques for extending the type system of C++ to support domain-specific abstractions. The main contribution is a programmable “subtype” relation. As a demonstration of the techniques, we implement a type system for defining type qualifiers in C++, as well as a type system for the XML processing language, capable of, e.g., statically guaranteeing that a program only produces valid XML documents according to a given XML schema.     

Distributed programming with Logic Tuple Spaces

From the point of view of distributed programming one of the most interesting communication mechanisms is associative tuple matching in a shared dataspace, as exemplified in the Linda coordination language. Linda has been used as a coordination layer to parallelize several sequential programming languages, such as C and Scheme. In this paper we study the combination of Linda with a logic language, whose result is the language Extended Shared Prolog (ESP). We show that ESP is based on a new programming model called PoliS, that extends Linda with Multiple Tuple Spaces. A class of applications for ESP is discussed, introducing the concept of “open multiple tuple spaces”. Finally, we show how the distributed implementation of ESP uses the network version of Linda’s tuple space.     

Active rules for XML: A new paradigm for E-services

XML is rapidly becoming one of the most widely adopted technologies for information exchange and representation. As the use of XML becomes more widespread, we foresee the development of active XML rules, i.e., rules explicitly designed for the management of XML information. In particular, we argue that active rules for XML offer a natural paradigm for the rapid development of innovative e-services. In the paper, we show how active rules can be specified in the context of XSLT, a pattern-based language for publishing XML documents (promoted by the W3C) which is receiving strong commercial support, and Lorel, a query language for XML documents that is quite popular in the research world. We demonstrate, through simple examples of active rules for XSLT and Lorel, that active rules can be effective for the implementation of e-commerce services. We also discuss the various issues that need to be considered in adapting the notion of relational triggers to the XML context. Received: 30 October 2000 / Accepted: 19 December 2000 Published online: 27 April 2001     

To secure XML documents with the extension function of XSLT

XSLT is a very popular and flexible language for transforming XML documents which provides a powerful implementation of a tree‐oriented transformation language for transmuting instances of XML using a single vocabulary into a desired output. In this paper, we propose a processing model that enables the XSLT processor to encrypt and decrypt XML documents. The details of the implementation are presented. Our model supports a more general encryption scope than previous models. The implementation and experimental results demonstrate the practicality of the proposed model. Copyright © 2006 John Wiley & Sons, Ltd.     

The Query Language to XML Documents Connected by XLink Links

The XML linking language (XLink) is a language for describing links between resources by means of XML attributes and a special namespace. The specification of the XLink language developed by the World Wide Web consortium provides only data structures for describing links and a minimal model of their behavior. In this paper, a language that allows the application to transparently formulate queries to XLink links and traverse the arcs determined by these links is suggested. The suggested language was named XPathLink, since it was developed as a natural extension of XPath, the language for addressing structural parts of XML documents. The XPathLink encapsulates complexities of XLink syntax from the application and provides a higher abstraction level when processing a set of XML documents connected by XLink links compared to the existing approaches. An implementation of the suggested XPathLink language by functional methods is considered. The functionality of the query language to XML documents connected by XLink links is achieved owing to the integration of the suggested implementation with the general-purpose programming language Scheme at the level of nodes of the processed XML documents and Scheme functions.__________Translated from Programmirovanie, Vol. 31, No. 3, 2005.Original Russian Text Copyright © 2005 by Lizorkin.     

以XML文档发布关系数据

本文对以XML文档发布关系数据的新技术进行了综述，主要分析了两种发布关系数据到XML文档的语言描述及其实现技术，以及它们的优缺点，一种是利用并扩展SQL的功能来描述这种转换，嵌套的SQL表达式被利用来描述嵌套，扩展的SQL标量及聚集函数被利用来描述XML元素构造，实现将关系数据转换为XML文档，另一种是利用RXL（Relational to XML Transformation Language)语言来定义一个关系数据库的XML视图，该XML视图是虚的，其它应用可再利用XML查询语言XML－QL在虚拟的视图上构造一个查询，抽取XML视图中的数据片断并对抽取的部分进行物化，实现将关系数据转换为XML文档。