F. C. Knabe. Language Support for Mobile Agents. PhD thesis, Department of Computer Science, Carnegie Mellon University, 1995.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....described in this paper is based on one of our current research projects in the context of the mobile agent system Tracy. 1 Motivation Over the past years, research in the area of mobile agent technology as a new paradigm of distributed programming has focused on suitable programming languages [5, 11] and languages for agent communication [1] Very much e ort was put into security issues [18] control issues [2,16] and in agent cooperation [13] Several prototypes of real world applications in the area of information retrieval, management of distributed systems, and mobile computing are in ....

F. C. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, Paittsburgh, Pa., Dec. 1995.

....and to an application. Dynamic loading is clearly necessary. Our de nition of active networking requires that it be possible to load functions while the system is running. Dynamic loading is a name for this ability. While it would be possible to represent active programs heterogenously [3], it adds considerable complexity to the system. For this reason, we have chosen to require that programs be represented in the same form regardless of the hardware present at any node that the program transits. In particular, this means that we will be transmitting an intermediate representation ....

F. C. Knabe. Language Support for Mobile Agents. PhD thesis, CMU, Dec. 1995.

....of typecase. His coercions serve the same purpose as our brackets, but his use of the closed scope open construct instead of dot notation prevents any possibility of sharing values of abstract type between instances. Typed channels Several languages, e.g. JoCaml [14] Nomadic Pict [27] Facile [30, 15], implement typed channels. These permit type and abstraction safe communication once the channel is established. Establishing a channel at an abstract type, however, requires the endpoints somehow to share the type already; in the case that the endpoints reside in different programs or ....

F. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, Dec. 1995.

....generating confusion since there is a mix of concepts and notions that belong to two different layers, i.e. the layer providing code mobility and the one exploiting it. Finally, there is no definition or agreement about the distinguishing characteristics of languages supporting code mobility. In [23], Knabe lists the essential characteristics of a mobile code language. They include support for manipulating, transmitting, receiving, and executing code containing objects. However, there is no discussion about how to manage the state of mobile components. Other contributions [24] 12] ....

....but system resources whose bindings are always removed upon migration. 3.3.3 Facile Developed at ECRC in Mnich, Facile [31] is a functional language that extends the Standard ML language with primitives for distribution, concurrency, and communication. The language has been extended further in [23] to support weak mobility. Executing units are implemented as threads that run in Facile CEs, called nodes. The channel abstraction is used for communication between threads. Channels can be used to communicate any legal value of the Facile language. In particular, functions may be transmitted ....

# F.C. Knabe, "Language Support for Mobile Agents," PhD thesis, Carnegie Mellon Univ., Pittsburgh, Penn., Dec. 1995. Also available as Carnegie Mellon School of Computer Science Technical Report CMU-CS-95-223 and European Computer Industry Centre Technical Report ECRC-95-36.

....[MMS95b] computingScience :Site(Tuple persons :Persons . end) administration :Site(Tuple insertAll( Addresses) Ok . end) Abstracting from the (significant) differences in typing and naming, this programming style is very similar to the one used in Telescript [GM95a] Mole [Hoh95] Facile [Kna95] or Obliq [Card94] Unfortunately, such a programming style does not scale well to cooperative information systems since it inherits many of the deficiencies described in the previous section: the agent accesses directly through methods (admin.insertAll) or even through unprotected database ....

Knabe, Frederick Colville. Language Support for Mobile Agents. Ph.D. Thesis, Carnegie Mellon University, Pittsburgh, PA 15213, October 1995.

....of a purely functional language to make more direct use of computational resources. To address these demands, the integration of functional, imperative, concurrent and distributed paradigms have been explored through implementations of languages such as Concurrent ML [13] Poly ML [14] Facile [15, 16], Concurrent Haskell [17] Erlang [18] the Joincalculus language [19] and PLAN [20] Understanding the fundamental ideas of these languages can provide insight into the question of how well the benefits of functional programming languages can carry over to programming languages for mobile ....

....Research Centre 10 (ECRC) refined and implemented the language and the Facile Antigua Release was made freely available in 1994. Facile was implemented as an extension of the Standard ML of New Jersey compiler [53] It was developed further by Knabe to support the mobile computation paradigm [16]. A major principle in the design of Facile is the symmetric integration of different programming paradigms so that every paradigm can use any other paradigm as a subcomponent for its expression. For example, a function may be implemented as a system of communicating processes and the internals ....

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F.C. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, Pittsburgh, PA, USA, Dec. 1995. 24

....problem of statically estimating potentially mobile functions and channels in the framework of Mobile . The estimation of mobile entities can be useful for compiler optimisations. We can provide supporting evidence for this argument by considering the implementation of the Facile language by Knabe [11] which facilitates the transmission of mobile agents across a network of heterogeneous nodes. In this language, users are required to provide annotations to identify potentially mobile functions so that the compiler generates a standard transmissible representation for these functions. The code ....

....is meant by potential mobility of functions and channels throughout the paper. We follow closely the criteria determined by Knabe to guide programmers in identifying potentially mobile functions in his implementation of Facile. The examples are also inspired by the discussion in his dissertation [11]. In the following section we will define Mobile a formal language which is suggestive of an intermediate language for Facile like languages. For the purposes of this section, it is sufficient to note that the language has operators and corresponding to sending and receiving a value and ....

F.C. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, Pittsburgh, PA, USA, Dec. 1995.

....and receiving values over typed channels. The emergence of the mobile computation paradigm has now opened up a new avenue for investigating how well the benefits of features from functional programming languages carry over to programming languages for mobile computation. Knabe s Facile [3] constitutes a good example for this. It takes the original Facile system [4] as its departure point and by reusing several parts of its design and implementation arrives at a language which is particularly well suited for the construction of mobile agents. The Facile language combines Standard ML ....

....based on CCS and its higher order mobile extensions (CHOCS and the calculus) 6, 7] and has a well defined semantics [8] This makes Facile an apt choice to use as a basis for obtaining insights into the problem of integrating functional and mobile computation. It is demonstrated by the work of [3] that the first class nature of functions would prove to be very convenient for representing mobile agents if one could successfully deal with a key issue in mobile computation, namely the heterogeneity of network nodes. By heterogeneity we mean that different nodes of a network may be of ....

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F.C. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, Pittsburgh, PA, USA, Dec. 1995.

....as described in Section 2.9.3, but not sufficient on its own to solve the problems that DCDO technology is designed to solve. 7.1. 3 Mobile Agents and Transmissible Code A mobile agent is a code containing object that may be transmitted between communicating participants in a distributed system [39]. Systems that support mobile agents must contain a mechanism for representing code so that it can be transferred from one program to another, over a network, and executed by, or within, the receiving program. Systems that provide this ability can be characterized along several dimensions, ....

....can be transferred from one program to another, over a network, and executed by, or within, the receiving program. Systems that provide this ability can be characterized along several dimensions, including the format or style of the transmitted code, and the initiator of the transmission. Knabe [39] identifies four different kinds of transmissible code representations source code, interpreted intermediate representation, compiled intermediate representation, and machine code. REV [65] Avalon Common Lisp [20] TACOMA [36] and SafeTCL [14] transmit source code, which is executed via ....

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Knabe, F.C., "Language Support for Mobile Agents," PhD Dissertation CMU-CS95 -223, Carnegie Mellon University, December 1995.

....other mobile agent systems such as TACOMA[44,45] Agent Tcl[36] and Telescript[92] is the use of interpreted execution for agents. In our intended application domain, this model fails to meet the performance requirements of most users. One system that overcomes this limitation is Extended Facile[48], an agent programming system based on the Facile functional programming language. In Extended Facile, agents are firstclass functions that may be transferred to remote nodes for execution. The code for agent functions in Extended Facile can be transferred in a higher level, platform independent ....

F.C. Knabe, "Language Support for Mobile Agents," PhD Thesis, School of Computer Science, Carnegie Mellon University, available as Technical Report CMU-CS-95-223, December, 1995.

....agents because they only have access to explicitly granted resources . Facile has been used to implement distributed teleconferencing and graphics applications. Facile can be considered a tool which supports the development of agents, rather than an agent language itself. For instance, Knabe [28] has used Facile to implement a Mobile Service Agent (MSA) capable of various tasks in the network domain. Java: Java [19] was developed by Sun Microsystems as a exible object oriented language with a wide application sphere. Java programs are compiled to byte code by the Java compiler. This can ....

F. Knabe, "Language Support for Mobile Agents", PhD thesis, CMU, December 1995.

....environment through the Interface Definition Language IDL. IDL is for Corba what HTML is for the Web and therefore it does not address any mobility issues. Facile [40] 124] is an extension to ML with multiple processes and communication. Facile has been enriched to support weak mobility [66], in a distributed name space scheme. Executing units are implemented as processes which communicate via channels. Once a piece of code has been transfered, the channel is closed and the receiver may chose to send it to another node to be evaluated. Apart from being non deterministic, Facile is ....

F.C. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, Pittsburgh, Pennsylvania, 1995.

....environments at least requires a global model of agent state as well as a transfer syntax for this information. Moreover, an agent system must provide functions to externalize and internalize agent state. Only few languages allow to externalize state at such a high level, e.g. Facile [Knabe95] or Tycoon [MaMaSc95] Since the complete agent state (including data and execution state) can be large in particular for multi threaded agents strong migration can be a very time consuming and expensive operation. These difficulties have led to the development of the so called Weak Migration ....

F. Knabe. "Language Support for Mobile Agents", PhD dissertation, School of Computer Science, Carnegie Mellon University, 1995.

....of a common execution environment reduces the problem to one that can be solved via a homogeneous migration solution. This approach was initially used by Chameleon [12] Today it is widely used by mobile agent systems, such as Agent TCL [16] Aglets [18] ARA [22] Concordia [11] Extended Facile [23], Liquid Software [13] Mole [2] Obliq [5] Odyssey [15] Omniware [20] Sumatra [1] TACOMA [39] and Telescript [40] Despite this approach s simplicity it suffers performance penalties from the use of a virtual machine. Some solutions [20, 13] alleviate this problem by using on the fly ....

F. Knabe. Language Support for Mobile Agents. PhD thesis, School of Computer Science, Carnegie Mellon University, 1995.

....transparent object migration. By contrast, recent approaches to logical mobility focused initially on the design of new languages or on the extension of already existing languages with primitives expressly conceived for handling logical mobility. This is the case of Telescript [50] and Facile [23], among the others. The creation of a brand new language was justified by the absence, in traditional languages, of hooks into the runtime support to enable relocation of code and state. The fact that today these systems, that nevertheless influenced heavily subsequent developments, are relegated ....

F.C. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon Univ., Pittsburgh, PA, USA, December 1995.

.... to evolve separately from one another without causing undefined function errors [8, 15, 25] Dynamically linked libraries partition a program into parts that can be built and changed separately [33] And mobile agent systems transfer runnable code between active entities in a distributed system [1, 2, 7, 18, 19, 29, 35]. However, these approaches alone are inappropriate for heterogeneous distributed object computing systems. Each requires a single common source language (Java, Kali Scheme, Erlang, and mobile agents) computer architecture (COM) or software environment (dynamic linking) Furthermore, with COM ....

Knabe, F.C., "Language Support for Mobile Agents," PhD Dissertation CMU-CS-95-223, Carnegie Mellon University, December 1995. LEWIS & GRIMSHAW 12

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F. C. Knabe. Language Support for Mobile Agents. PhD thesis, Department of Computer Science, Carnegie Mellon University, 1995.

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Knabe, F. C. (1995). Language Support for Mobile Agents. PhD thesis, School of Computer Science, Carnegie Mellon University.

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Knabe, F.C., Language Support for Mobile Agents, PhD Thesis, Carnegie Mellon University, Dec. 1995.

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F. Knabe. Language Support for Mobile Agents. PhD thesis, Carnegie Mellon University, December 1995.

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Knabe, F.C., Language Support for Mobile Agents, PhD Thesis, Carnegie Mellon University, Dec. 1995.

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Knabe, F.C., Language Support for Mobile Agents, PhD Thesis, Carnegie Mellon University, Dec. 1995.

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Knabe, F.C., Language Support for Mobile Agents, PhD Thesis, Carnegie Mellon University, Dec. 1995.

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Knabe, F.C., Language Support for Mobile Agents, PhD Thesis, Carnegie Mellon University, Dec. 1995.

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Knabe, F. C. Language Support for Mobile Agents, Ph.D. Thesis, Carnegie Mellon Univer- sity, Pittsburgh, PA, 1995.

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