which various names: mobile agent dock, platform, server, and must be ..... asynchronous message passing (ordinary SMTP) between anchored ... when the worker was more an artisan than the mass production ..... can be viewed as a more complex mailing daemon and interface, ... âMobile Agents: Are They a Good Idea?
Mobile Agent Support for Tracking Products in Virtual Enterprises N. B. Szirbik J. B. M. Goossenaerts
D. K. Hammer A. T. M. Aerts
Department Information & Technology Eindhoven University of Technology Postbus 513, 5600 MB Eindhoven tel: +31 40 247 {4370, 2062}
Department of Computer Science Eindhoven University of Technology Postbus 513, 5600 MB Eindhoven, The Netherlands tel: +31 40 247 {2734, 2759}
{n.b.szirbik, j.b.m.goossenaerts}@tm.tue.nl
{hammer, wsinatma}@win.tue.nl
ABSTRACT Mobile Agent systems appear to be a suitable approach for a large range of applications, differing in scale and construction. We are investigating the application of mobile agents within a Virtual Enterprise. Here, a promising idea is to map mobile agents to products and parts of products, which are moving across the enterprise. We identify certain advantages of this approach, like simplicity, robustness and flexibility. In the last part we mark some issues related to the needed information infrastructure.
Keywords Mobile agents, manufacturing oriented virtual enterprises, monitoring by tracking.
1
INTRODUCTION
Agent-oriented technologies, currently used for the development of flexible information systems [27], are a convenient way to model and analyse complex environments like economic markets, interorganisational workflows and autonomous robots. Two different paradigms have emerged from the initial agent-based models [16] applied to Enterprise Information Systems (EIS): the static agent paradigm, and the mobile agent paradigm. The latter presumes that whole agents are moving over a network, not driven by external forces, but by their internal decisions. Also, the internal status (the value of member variables) of the agent is preserved. We not consider here the case of preserving the execution stack and program counter (transparent mobility). To assure mobility, a computational facility which is providing execution support for an agent must offer services for the agent to migrate, communicate, and authenticate itself [5]. These services are usually encapsulated in a software package which various names: mobile agent dock, platform, server, and must be present and active on the computational facilities which are interesting for the mobile agents to be visited. There is noticeable interest on the market for such platforms;
existing ones are used nowadays in research projects and industry applications. Mitsubishi Concordia, IBM Aglets and Object Space Voyager are a few examples of first generation packages available. The MELBA system [1], developed on Concordia platforms, is using mobile agents for integration of extended enterprises. But the majority of the applications are intended only for asynchronous remote database querying (like in [3]) and information gathering systems [21] in wide area networks (including Internet). In the current domain of co-operation between enterprises, the main focus is on product development and concurrent engineering. This is realised through CAD data exchange, Virtual Design Rooms, various capability assessment methods, standardised structures for work breakdown and organizational breakdown and enhanced digital communication. We consider that this view is only a half of the picture, because the manufacturing process of a product by a group of enterprises which are not forming a long-lasting consortium and are not highly integrated is a difficult task also. Such a process can be easily affected by delays, and the lack of communication and upto-date information at different decision points can lead to situations which are worse. In this paper, we propose a new idea: to use the mobile agent as a tracking mechanism in heterogeneous, widely distributed Virtual Enterprises. We show how this mechanism will enhance the availability of information to the decision makers, and simplify the problem of the visibility of information in a Virtual Enterprise. In section 2, three possible models of the Virtual Enterprise are presented, along with the idea of flat Meta-Control. In section 3, the differences between the static and mobile agent based systems are investigated. In section 4, we show where, how and why the mobile agents are used. Also, we discuss the levels of complexity of the system which are induced by the possible missions an agent can have. In section 5, we shortly address the infrastructural requirements for such a mobile agent system. Section 6 concludes about the advantages of the mobile agent based systems and presents some future and related research possibilities.
2
MODELS FOR VIRTUAL ENTERPRISES
The Virtual Enterprise (VE) discussed in this paper is an ensemble of different autonomous parties involved in the manipulation of physical goods, i.e. manufacturing, assembling
and transportation of items. Of course, this is very vague, for a more detailed proposal for possible definitions, see [6] and [26]. But the view here is on the concepts of autonomy and manufacturing-oriented. Also, our emphasis is on globally distributed VEs. We present solid arguments that mobile agent technology can enhance data exchange, cooperation and coordination between the parties. There are many models possible for VEs [26], depending on their particular business, their scale, and the technology used. In the following we present three typical cases.
2.1
Hierarchical Virtual Enterprises
Such an enterprise is formed around a single organisation, which is in charge of distributing the manufactured goods to the customers. The produced artifacts, however, are a result of a chain of processes, which can take place in very different places. For example, fashion clothes can be designed in Paris, textiles can be purchased from suppliers in Asia, transported to the place of manufacturing in the Middle East and distribution can take place in Europe and North America according to customer demand. All this workflow is possible without the parties involved in the overall process needing to know of every other one. If a “leading” firm is negotiating bilateral contracts with each of the above mentioned parties, is performing co-ordination and represents the front-end to customers, that firm can be viewed as a VE control entity. It is interesting that this firm is dealing mostly with information and not the physical processes involving in manufacturing. The hierarchical control is not explicit and transparent, the leading company behaving like an “invisible hand”. New information technology tools and digital communications enabled the flourishing of this kind of business. However, it is hard to believe that at the current level of technology and market reality this model can be applied to complex manufacturing processes, for example to automobile or to aerospace industry.
2.2
The differences between the Transaction-based Market, the Supply Chain, the Extended Enterprises and the VE are blurred and sometimes these terms are used intercheangeably. In our view, the typical features of a generic VE are: the opportunistic approach to new product development, short term commitments, and partially commitment. That is, a party within a VE is not fully dedicated to that particular VE. Usually, only a small percent of the resources are allocated to a particular product- oriented VE. A company could be part of many totally different VEs in the same time. This situation shows how hard the process of integration could be. Also, we explain in section 3.3 that a high degree of integration can lead to a lack of flexibility. However, our goal is to obtain some degree of integration.
2.4
What is important to mention here is that the VE can be identified by a certain product or family of products (or generic product, see [13]). When a product is composed of 100 parts, the VE associated with it is composed of the enterprises that manufacture, assemble, transport and service these parts.
“Integrated” Virtual Enterprises
The above case is one of a weakly integrated VE. The detailed overall behavior of this kind of VE is emerging from the sum of all its parts, mostly as a result of the manner in which the parties are co-operating. Being a complex organisation, subject to
Meta-Control
In a globally distributed VE, an explicit hierarchical and transparent control structure is not only undesirable, but also impossible. The parties involved wouldn't give up, even partially, their autonomy. However, due to the uncertain and highly distributed nature of the processes involved, a meta-control (sometimes called self-control) mechanism could be accepted [14]. This mechanism must work without an expensive infrastructure and organisational effort, and most important, without infringing on the autonomy of the VE parties. Typical approaches insist on EDI-based methods. In our view, two generic conditions are necessary for this kind of meta-control: -
The decision-makers within the parties of the VE have to be aware of "global viewpoints". This can be achieved, for example by constructing Common Shared Perspectives (CSPs) [9] about the status of the VE.
-
The information of the individual parties that is relevant for the overall control has to be visible across the VE domain.
Product Oriented Virtual Enterprises
In certain situations, especially for the customer-driven, produceto-order artifacts, manufacturing firms rely on subcontractors for producing parts of the final product and additional services. The subcontractors have their own suppliers of manufactured parts or raw materials. These enterprises, together with the transportation parties and in some cases distributors and final retailers, form a value-chain, which can be depicted as a decomposition tree. The root node of this tree is the enterprise that makes the final assembly. It could be that this kind of VE is only the result of bilateral contracts between parties. The communication and cooperation is enabled on the basis of, e.g., EDI. However, some vital information can be passed between more than just two of the parties involved, but this without being regulated a priori.
2.3
fluctuations and uncertainties, it can not be expected to show (after a localised peer-to-peer tuning in the starting phase) an ideal global behavior [9]. A desirable case is when the parties are commonly agreeing about some co-ordination aspects. This implies legal, organisational and technical issues. In this paper we focus only on the technical issues, being aware that the other two are also very important and part of them solved already.
The CSP is a concept used in flat control models. The business management processes in a VE are highly distributed and the awareness of the decision-makers about the status of the other parties is low. A favourite idea for overcoming the latter problem is the Virtual Management Room, an infrastructure able to put the decision-makers across the VE in permanent multimedia contact. However, as attractive it may be, we believe that such a scheme requires a very high degree of synchronicity and thus is a waste of time of the decision-makers. Fixing certain problems which appear during artifact manufacturing actively involves usually only a small number of parties (two or maximum three). But being aware of them is important for many others, in terms of repercussions and influences across the value chain (see [8]). From the logistical control point of view, data about the status of products currently in the making is the most relevant.
3
STATIC AND MOBILE AGENT-BASED INFORMATION SYSTEMS FOR VIRTUAL ENTERPRISES
In an agent approach for a VE, parties are modelled as agents. Software packages are implemented for acting as goal-driven, reactive and pro-active agents, and subsequently both communication and co-operation can be automated and enhanced. The agents are acting on behalf of humans, and also supporting human decision-making processes. From a functional point of view, the activity of the agents is mainly around eventnotification, information gathering, and the permanent activity for keeping the CSP up-to-date. It may be envisaged that in the future the agents will take care of more and more implicit activities concerning negotiation, collaboration and scheduling and even decision-making (which raise the organisational question of how much authority can be entrusted to the agents). At present, however, the emphasis, is on monitoring. But in a VE, the task of getting the right information at the right time to the right people is not a simple one [6].
3.1
The Static ABIS Concept
From our point of view, the main reason for an Agent-Based Information System (ABIS) built within a VE is for helping the decision-makers to obtain pertinent, consistent, up-to-date information across a large and complex VE. The very simple way to create an ABIS is to use the static agent paradigm, implementing the software agents as resident packages within local ISs. These components of the IS (ideally plug-and-play components) notify other agents in the ABIS of events, request information, update data and interact with human users. At first sight, the necessity for mobile agents is not quite obvious. But a deeper analysis of the static ABIS model reveals three problems: a. Maintenance and improvement of an ABIS like this is very costly. For example, the introduction of a new version of a kind of agents must be realised on all computational facilities where that particular type of agent is resident. Keep in mind that the VE is scattered all around the world, and some parties may have not the necessary IT-support to install the new version. Even in the plugand-play case, some adaptation and configuration for local needs can lead to difficulties [17]. b. Communication between parties can be costly, unreliable and can lead to excessive network use, especially if the communication is connection-oriented. Communication bottlenecks can influence negatively the ABIS performance and even the desired functionality [27]. c. The unavailability of network connections and computing facilities (e.g. mobile computers) can lead to serious performance problems, especially if some of the communication is synchronous. In contrast, mobile agents can support dynamic configuration, automated versioning and remote installation, dynamical addition of new functionality to remote computational facilities, increased asynchrony and robustness, disconnected operations and reduced network use [12]. But if we use mobile agents only to enhance the maintenance and versioning of the ABIS components, the resulting system will in principle, is the same as the one with purely static agents. The single difference is that the packages of the agents now can be remotely installed.
3.2
Arguments for a Mobile-ABIS
In order to improve the operation of the VE, we must use mobile agents, which are moving from one machine to another, instead of sitting anchored at one site and requesting remotely located data by synchronous protocols. Unfortunately, it is not very clear how, where, and especially for what purpose, mobile agents must be used in such an environment. In the literature, the proposal to use mobile agents in a VE appeared three years ago [22]. But no progress was made in this direction, even in terms of general paradigms. For example, the idea to make a hybrid system, in which static agents are sending mobile agents to gather difficult and costly reachable information, is quite forced. A closer look to this idea shows that the same result can be achieved by using asynchronous message passing (ordinary SMTP) between anchored agents. It is easy to put the intelligence in the quasistatic agents and not in the messages of the ABIS. What is needed here is a conceptual improvement of the ABIS model. Our idea is to modify the general view of the mapping of the agents onto the real world. The idea has come up while studying the feasibility of deploying mobile agents in a shop floor system, where a static agent control system was used. The typical approach is using static agents, mapped onto the cells in the shop floor [28]. Every agent is in charge of certain operations, and is continuously negotiating with the rest of the agents, helped sometimes by a meta-controlling agent, in order to achieve the overall goals. This is analogous to the situation in which workers in a workshop are highly specialised in specific operations. But trends in modern manufacturing are different now. Highly skilled workers are more and more specialised in certain types of products instead of repetitious operations on a single machine [6]. Lean production, automation of the machines at the shop floor and customer-driven manufacturing forced the manufacturing organisation to teach the workers to become more involved in the overall process of making of a product [4]. Historically, this is a return to the era when the worker was more an artisan than the mass production anonymous worker on the assembly line. In a VE is impossible to link a product to an artisan worker, due to the distribution of the product manufacturing process. But an information entity can link the decision makers- interested in a certain product. In this context, it is very natural to relate the mobile agent to a product that defines its own production process, e.g., in form of a workflow. The result is that the product controls its own production process using the available cells and machines. This is yielding a very generic and flexible approach, when the workflow also supports exception handling and human intervention [25]. There are also other advantages, especially related to the simplification of the agent-based system architecture and the flexibility to introduce new products into the manufacturing process. The shop floor case is a very specialised example of using mobile agents. The agents are roaming only through a LAN formed by the computational facilities of the cells in the shop floor. Here are no problems with unreliable communication, latency and disconnected sites. The real advantages of the mobile agent technology can emerge when used at a bigger scale.
3.3
ABIS for VE integration
The parties in a VE have different information systems. In an integrated VE, where the information systems contain agents used for communication and co-ordination, the set of agents may be viewed as an IS supporting the VE as a whole. The agents have common semantics for communication at knowledge level (e.g. KQML) and are able to perform co-ordination of some operations of the VE. This is realised usually by the Contract-Net-Protocol or other kinds of auction-based schemes. What is very problematic is that such an ABIS must cope with a lot of unexpected situations, and this prohibits to design the entire program-logic to solve them. Also, every party, which is entering the VE, must install the agent software. As explained previously in section 3.1, this can create a lot of difficulties. New products and strategies in the VE are putting a continuous pressure on the development of the new agent capabilities. These can grow very complex, resource consuming and perhaps unreliable. Another critique of the current ABIS models (for details of this critique see [18]) is that very little effort was made to resolve the human-agent interaction. Conceptually, the agents are communicating between them and with the information system where they are based. To some extent, the agents are behaving like social entities, mimicking human activities like co-operation. But this picture is somewhat ruptured from the world of human decision-makers, who in fact are responsible for the business management in the VE. We believe that research must be done in the direction of studying the interaction between the humans and agent systems working in complex organisations. There is a dichotomy between the opportunistic, product-oriented VE and the envisaged highly integrated VE through static agents. As a VE is becoming more and more integrated, it becomes proportionally harder for new parties to enter or leave (due to previous integration investments and learning costs). That leads to a “frozen” state of the VE, totally against the openness and structural flexibility that is needed in a VE. Also, this trend can reduce the ability of the enterprise to launch new products, which need the expertise and capability of enterprises outside the current boundaries of the integrated VE. Of course, for long term projects, where the parties are fully commited to a complex and particular project (e.g. a new airplane) it is better to have a integrated VE, but this situation is near to other business organisational concepts, like the Consortium or the Extended Enterprise [4].
3.4
Delays, Redundancy and Flexibility
Because a product-oriented VE is an opportunistic organization, taking advantage of niches on the market, strict delivery dates are imposing a crucial feature: delays are not permitted. A lost due date can produce only dead stock. Consequently, the MobileABIS must be developed keeping in mind this strong requirement. The decision-makers are the first responsible for respecting the schedules and finding solution to avoid delays. They are also the first who must take full advantage of the capabilities of the MABIS. Another important feature of the VE is the high level of redundancy of parties with similar capabilities. According to their production structure, turnover, stocks, and workload of the manufacturing resources, they can participate or not in the process
of executing new orders. If, during the manufacturing, transportation, and distribution of the product, one of the parties is not able to participate at that moment, the VE strategy is to find other alternatives on the fly. From the redundancy and flexibility points of view, the model of a product-oriented VE is more attractive. The point is that we can have a separate sub-VE for every product, which is manufactured in the bigger VE. The problem of the complexity of the information infrastructure, however, remains the same.
4
PRODUCTS AND MOBILE AGENTS
Unfortunately, there is little experience accumulated regarding a methodological design of a Mobile-ABIS. We put three research questions: where, how and why mobile agents are to be used. First question is answered by explaining the mapping of the agent onto the physical realm. The second is answered by the schema used for deployment into the network formed by the VE. The last asks about the mission of the agent.
4.1
Mapping the Mobile Agents to Physical Entities
Parties within the VE can use different frameworks for developing their own IS. Examples of such frameworks are CIMOSA and ARIS for enterprise modeling and CALS for product life-cycle modeling. A sound way of thinking is to design the Mobile-ABIS using a more general framework, which encompass the generic features and mechanisms of the models within the boundaries of the envisaged VE. Such a framework is the MiViPoRo [10]. It is a layered structure, dividing the generic domain of manufacturing industry in four activity layers (inovation, improvement, operation and observation) and two sub-domains (physical and cybernetic). In the operational layer, MiViPoRo is introducing the concept of proxy. Proxies are an “informational reflection” of the physical entities in the organisation. People are “mirrored” as actors, artifacts as props, and manufacturing cells as stages. For every entity in the physical domain we should have an entity in the cybernetic domain. The idea of merging the mobile agents’ paradigm with a generic framework was firstly investigated in [11]. The framework, which is result from a technology-independent reflection for knowledge systematisation, it is at a higher level of abstraction than a mobileagent framework, which is more about design and implementation issues. But both have in common the concept of spatial mobility. A common sense observation is that is possible to have linked mobile physical entities and self-contained mobile information entities. Here we are proposing to link a final artefact (a product of VE and its parts) to a set of mobile agents. These are monitoring by tracking the overall process of manufacturing that specific product. Other physical entities than the products have the mobility feature. In a strongly integrated organisation, it is also possible to link all types of proxies (actors, props and stages) to mobile or static agents. But this can lead to a research task of a greater magnitude. Hence, our approach is to implement only the props as mobile agents.
4.2
The Life-Cycle of Mobile Agents: a Simple Case
When the product-oriented VE receives a customer order for a single product, the manufacturing process could be a one-of-a-
kind or a custom-build-of-options one. We assume that the product strategy definition phase and the product development and engineering are completed. That means that every party of the VE has the expertise and manufacturing resource to fulfil its part of the overall job. Also, the throughput times and the costs are clearly established. To close the deal with the customer, the sales party of the VE has to perform a so-called ATP (Available to Promise) Check. This is necessary to see if the customer order is deliverable on due date. However, this is a very difficult task, more complicated in a VE than in a single integrated company. The use of mobile agents in this case was investigated in [2]. Combined with deployment of ADI (advanced demand information, see [7]) this is another field for future research, strongly linked with the manufacturing process tracking. After the contract is signed, a firm order is released for the product. The Mobile-ABIS takes note about the order and creates a set of agents associated with that specific product and its parts. The Bill-of-Material (BOM) for the product contains all the information about the parts and the site location of the parties which are manufacturing, assembling and transporting these parts. Also, the agents contain data about the schedules and the routings of the parts w.r.t. the released order. After this preparation phase, the agents are deployed at the sites where the parts are executed. If we figure the BOM as a decomposition tree [13], every node of this tree has an agent associated with it. If more than one node is processed at a single physical site, the agents associated with these nodes can be merged in a single one. The agent associated with the final product is deploying himself at the site located at the point-of-sale (POS) of the product. A further possibility is to deploy a clone of this agent to the customer too (if there exists the minimal infrastructure for M-ABIS). After the deployment of the mobile agents and the decomposition of the final product order into orders for each party in the VE, some of them will start the manufacturing of their parts (the first time-phased leafs in the decomposition tree). Others can prepare with set-ups, or start purchasing in advance for necessary items. When a part is finished, and is moved to another location (party), to be processed further or to be assembled with another parts, the mobile agent associated with it migrates to the M-ABIS site of that location. The agents are crossing the boundaries of different parties, by tracking the parts of the product. The migration of the agents has the same workflow like the manufacturing of the product. It is possible that due to exceptions, the workflow is modified, and the agents must be able to cope with the change of their schedule and itinerary. When a group of agents are gathering at the same site (party), and their associated parts are assembled in a single one, the agent which was already docked there (and it is linked with the assembly), must merge with the arrived agents and migrate to the following site in the workflow. We are taking into account also the possibility for the agents to split, even if in this simple bottom-to-up assembly case, the possibility of divergent workflow is seldom. A specific example could be the X-ray examination of a high-risk part (e.g. a critical steel pipe in a nuclear plant), which is done usually by a third party, entrusted to give a legal approval of the usage of the manufactured part. In this case, a mobile agent that tracked the part has to send another mobile agent together with the photos to the site of the third party.
They will merge after the part is approved. A composite structure of the agent may be an answer for this problem of merger and split.
4.3
The Mission of the Mobile Agents
It is hard to state at the beginning of the research how complex the development of the M-ABIS will be w.r.t. the complexity of the mission of the agents. Hence, we propose a stage-based approach, each stage representing a more complex mission for the agents.
4.3.1
Enhancement of Situation Awareness and CSP
We envisage that in the first stage of the development of this model, the function of the mobile agent is to locally gather and request information about the status of its part, and to, proactively and on request, send data that is needed by the decisionmakers elsewhere. In this case the requirements for the mobile agents must be: -
Capacity to interact with the local IS (based on common ontologies).
-
Capacity of autonomous migration by tracking the associated part.
-
possible dynamic changes of itineraries and schedules
-
Knowledge about the decision-makers locations and their informational needs.
The requirements for the M-ABIS are: -
directory and trading service (white and yellow pages), to facilitate the location of agents and resources in the network,
-
a redundancy-based recovery mechanism,
-
security features,
-
a filtering static agent type for the human decision-makers, to enhance the transparent communication with the mobile agents.
This simple model is enhancing the Situation Awareness of the decision-makers in the VE, and simplifies the protocols needed in EDI. An interesting extension to this model could be the collaborative construction of a CSP about the status of a product. Software agents and humans can cooperate to construct a “document” that illustrates the CSP about a product-in-making at a given moment. An auxiliary task for the agents could be also the manipulation of the documents involved in the manufacturing (orders, invoices, reports, amendments to the contract, etc). In this case, the ordering process in the VE is automated; the deployment of the agents is having the effect of transmitting the orders. This process is linked also with the preliminary ATP check and ADI deployment.
4.3.2
Adaptivity
A more active (second stage) mission for the agent can be the gathering of information about the resources for the next step of processing (or transportation). The agents must contain knowledge about the possible alternative routings and have internal mechanism for re-routing and re-scheduling the manufacturing of the part. Of course, this must be done in collaboration by the entire group of agents involved for that specific product, in order to minimise the delays. It is also possible that the agents linked to a product be able to collaborate
with agents linked to another totally different product, to solve conflicts which arise when competing for the same manufacturing resource. The ISs within the VE can have local ERP capabilities, and it is wise for the agents to use them. Local solutions for re-planning can be useful for the solution of re-scheduling at a bigger scale. Also, the agents must be kept lean, because their mission is not to replace the local IS functionality, and a fat agent can pose problems when migrating through a slow and unreliable connection and use an unacceptable amount of local resources. However, our intention is to concentrate first on the problems that appear as a consequence of the requirements of the first stage. Though, even for the first stage, the single-product order case is too simple and specific, and it is necessary to take another cases into consideration.
4.4
More Complex Order Cases
The typical case is when the customer is ordering not only a single item of a product. The delivery can be on a single-item-at-a-time basis, with strict due times, or in time-phased batches. A specific variation is when all items of the order must be delivered at the same moment. Two approaches are possible in this case: -
To create a separate set of agents for every final item
-
To create an agent for every batch
The first approach is similar to the single-item order case. The danger is that orders containing large numbers of items will result in a deployment of a huge number of agents, leading to a high level of redundancy and the waste of computational and communication resources. The good thing is that the number of agents in the system is always predictable. Using lean agents, for small batches, this approach is straightforward. In the second approach, we identified the problem of fragmentation. For example if somewhere in the workflow, a batch requires a certain number of parts, and the local stock has a lower number, the batch size will be reduced for the moment, and the rest of the items are to follow later, when the stock is replenished. The finished batch can progress in the workflow to the following location (where the resources are prepared for). This means that the agent tracking the initial batch must split in two. The first agent will track the finished batch, and the second will remain until the rest of the items are finished. Expanding this scenario, it is possible to have more and more splitting points, resulting in an increase in the number of agents. Perhaps not the number of agents is dangerous here, but the manageability of communication and co-operation of the new appeared agents. The creation of this kind of splinter agents is non-deterministic. The selection of one of these two possibilities is case dependent, and a Mobile-ABIS must be able to use single product agents and batch agents in the same time, even for the same order. A higher level of hybridization is where agents allocated to diferent orders can co-operate, in order to fullfil their separate mission. If two separate VEs have the same Mobile-ABIS in use and a company is party in both VEs, mobile agents from these two can also cooperate in certain situations. Both approaches highlight the importance of information about the local stocks. The mobile agents must be capable of reasoning about the current level of stocks, safety values, replenishment
schedules, decoupling points, pallet capacity, transportation costs etc.
5
AN UNIVERSAL PLATFORM
A VE can be a dynamic organisation, parties entering and leaving all the time. In order to have a functional Mobile-ABIS, the local IS of the parties involved must be able to host the mobile agents. What is even more important, the platform must be uniform throughout the entire VE. This can be a very hard requirement, because the typical case is that the software packages used, even the basic ones, like the operating systems and the databases are completely different from one local IS to another. The only types of packages widely used nowadays, which can be termed as universal, are web browsers and Java Virtual Machines. These form a suitable base for the construction of more advanced platforms, which can support mobile agents [5]. The necessity for a standard platform resulted in proposals like [15] and [20], envisaging the concept of a new kind of universal mobile agent facility. To some extent, this mobile-agent platform can be viewed as a more complex mailing daemon and interface, receiving and sending not messages, but agents and also interacting with the user. Unfortunately, this concept has always been suspicious due to security concerns, because of malicious agents. Also, malicious platforms can give agents wrong information. Of course, certain measures for security, like firewalls and authentication are necessary. These kinds of measures are becoming more and more common, as also other networked activities, such as Electronic Commerce, become more important. There are also powerful theoretic approaches for the security. We point here two of them. To avoid the execution of malicious agents, a novel and elegant idea is to use Proof-Carrying-Code [19]. Every agent has a specification that can in the first step be used by a proving system of the dock to see if the agent is harmless. The second step is to verify if the code of the agent is conformant with the specification. For the agent security, the method of Undetachable Signatures [23] is considered a safe concealment of the data held by the mobile agent.
6
CONCLUSIONS
In conclusion, we state that a Mobile-ABIS with mobile agents executing their own workflow is a feasible development. This kind of Mobile-ABIS architecture has obvious advantages: robustness, dynamic configuration, reduced communications, an advanced and more elaborate offering of public information in the VE, and what is more important, a continuous support for the construction of CSPs for decision-makers. An interesting further development can be the tracking of a product during his entire life-cycle, not only until it reaches the location of selling, but also afterwards, in the utilisation phase [24], and even in the waste phase. An agent can provide important information for servicing the product, further sale, leasing, buyback, de-assembly and/or recycling, safe disposal, etc. Of course, this is possible only if the customer is capable of offering an appropriate platform and worthwhile if the product is an important investment asset. Related research must insist, among others, on an organisational structure for establishing the agent creation authority and a legal framework to impose the responsibility of correct and fair cooperation with the visiting agents for the various parties. From
the infrastructural point of view, the availability of a standardised and universal mobile agent platform is most desirable.
REFERENCES [1] *** http://www.concordia.mea.com/concordia/whats_new/ Press_release4.htm [2] Aerts A.T.M., Goossenaerts J.B.M., Mouws F., (1999), “The Salesman Case”, Technical Report, Eindhoven University of Technology, The Netherlands. [3] Bos, V., (1998), “Value Web Available to Promise”, Postgraduate Programme Report, Eindhoven University of Technology. [4] Browne J., Sackett P.J., Wortmann J.C., (1995), “Future manufacturing systems – Towards the extended enteprise”, Computers in Industry, 25, Elsevier, pp.235-254. [5] Dalmeijer M., Hammer D.K., Aerts A.T.M. (1999), "Mobile Software Agents", Computers in Industry, in press. [6] Davidow W.H., Malone M.S., (1992), Corporation”, Harper&Collins, New York.
“The
Virtual
[7] Donselaar K.H., Sharmon G., (1998), “Innovative Survey in the Transportation and distribution Sector” in International Journal of Physical Distribution and Logistic Management, vol. 28, no. 8, pp.617-629. [8] Euwe M., (1999), “Decentralized Control Systems for Logistical Coordination”, Ph.D. Thesis, Eindhoven University of Technology, The Netherlands. [9] Fischer K., Mueller J.P., Heimig I., Scheer A.-W., (1996), “Intelligent Agents in Virtual Enterprises”, Proc. of PAAM’96, London, pp.205-223. [10] Goossenaerts, J.B.M, (1997), “A framework for connecting work and information infrastructure”, in Information Infrastructure Systems for Manufacturing, Chapman&Hall, pp. 193-205. [11]
Goossenaerts, J.B.M., Aerts, A.T.M., Hammer, D.K., (1998), “Merging a knowledge systematisation framework with a mobile agent architecture”, Information Infrastructure Systems for Manufacturing II, by John Mills adn Fumihiko Kimura (eds.), Kluwer.
[12] Harrison C.G., Chess D.M., Kershenbaum, A., (1995), “Mobile Agents: Are They a Good Idea?”, Research Report, IBM Research. [13]
Hegge H.M.H., (1995), “Intelligent Product Family Descriptions for Business Applications”, Technical Report, Eindhoven University of Technology, The Netherlands.
[14] Jennings N.R., Faratin P., Johnson M.J., O’Brien P., Wiegand M.E., (1996), “Using Intelligent Agents to Manage Business Processes”, Proc. of PAAM’96, London, pp.345360.
[15] Joint submission - Crystaliz Inc., General Magic Inc., GMD Fokus, IBM Corp., (1997), “Mobile Agent Facility Specification”, The Open Group, OMG TC Document. [16] Kafura D., Briot J.P., (1998), “Actors and Agents”, IEEE Concurrency, vol.6/no.2, pp.24-28. [17]
Karnik N.M., Tripati A.R., (1998), “Agent Server Architecture for the Ajanta Mobile-Agent System”, Proc. of Int’l Conf. Parallel and Distributed Processing Techniques and Applications (PDPTA’98), CSREA Press, pp.63-73
[18]
Lingnau A., Drobnik O., (1998), “Agent-User Communications: Requests, Results, Interaction”, in Mobile Agents’98, LNCS 1477, Springer, pp.209-221.
[19] Necula G.C., Lee P., (1997), “Efficient representation and validation of logical proofs”, Technical Report CS-97-172, Carnegie Mellon University, Pittsburgh, PA. [20]
MASIF (1997) – Document ORBOS/97-10-05, http://www.opengroup.org/~dejan/maf/draft10
[21] Merz B., Liberman B., Mueller-Jones K., Lamersdorf W., (1996), “Interorganizational Workflow Management with Mobile Agents in COSM”, Proc. of PAAM’96, London, pp.405-420. [22] Morais de Assis Silva F., Krause S., (1997), “A Distributed Transaction Model based on Mobile Agents”, in Mobile Agents’97, LNCS 1219, Springer, pp.198-209. [23] Sander T., Tschudin C.F., (1998), “Protecting Mobile Agents Against Malicious Hosts”, in Mobile Agents and Security, LNCS 1419, Springer, pp.44-60. [24] Stahel W.R., (1999), “From Products to Services or Selling Performance Instead of Goods”, Tutorial Text, 1st Intl. Symposium on Environmentally Conscious Design and Inverse Manufacturing - EcoDesign’99, Tokio, pp.65-96. [25] Stiphout R. Van, Meijler T. D., Aerts A.T.M., Hammer D.K., Le Comte R., (1998), “TREX, Workflow TRansactions by means of EXceptions", WFMS'98 EDBT Workshop on Workflow Management Systems, , J. Eder, H.-J. Schek, L. Salsa, Eds., pp.21-26. [26] Thoben K.-D., Jagdev H., (1999), “Typological Issues in Industrial Collaboration”, Proc. of ICE’99, Amsterdam, pp.29-36. [27] Van Dyke Parunak H., (1998), “What Can Agents Do in Industry,and Why?”, Proc. of Cooperative Information Agents II, Springer LNAI 1435, pp.1-18. [28] Zwegers, A.J.R., Beukering, van, L.H.Th.M., Schenk Brill, van, D., Pels, H.J., (1997), “A Comparison of Three Agent Based Control Systems”, Proc. of ASI’97, pp.209-216.
