Ping LouÆZu-de ZhouÆYou-Ping ChenÆWu Ai
Study on multi-agent-bad agile supply chain management Received:23December2002/Accepted:23December2002/Published online:5December2003
ÓSpringer-Verlag London Limited2003
价格英语Abstract In a worldwide network of suppliers,factories, warehous,distribution centres and retailers,the supply chain plays a very important role in the acquisition, transformation,and delivery of raw materials and products.One of the most important characteristics of agile supply chain is the ability to reconfigure dynami-cally and quickly according to demand changes in the market.In this paper,concepts and characteristics of an agile supply chain are discusd and the agile supply chain is regarded as one of the pivotal technologies of agile manufacture bad on dynamic alliance.Also,the importance of coordination in supply chain is emphas-id and a general architecture of agile supply chain management is prented bad on a multi-agent theory, in which the supply chain is managed by a t of intelli-gent agents for one or more activities.The supply chain management system functions are to coordinate its agents.Agent functionalities and responsibilities are de-fined respectively,and a contract net protocol joint with ca-bad reasoning for coordination and an algorithm for task allocation is prented.
Keywords Agile supply chainÆMulti-agent systemÆCoordinationÆCBRÆContract net protocol
1Introduction
Advanced technology and management are constantly being adopted to improve an enterpriÕs strength and competitive ability in order to achieve predominance among hot global competition.In a report on21st century manufacturing strategy development,the author suggests that various production resources,including people,funds,technology and facilities should be inte-grated and managed as a whole;thus optimising the utilisation of resources and taking full advantage of advanced manufacturing technology,information tech-nology,network technology and computer[1].Agile manufacture bad on dynamic alliance is coming into being so that enterpris can remain competitive in a constantly changing business environment and is becoming a main competitive paradigm in the interna-tional market.Agility,which has basically two mean-ings:flexibility and reconfigurability,has become a very important characteristic of a modern manufacturing enterpri.Flexibility is an enterpriÕs ability to make adjustments according to customersÕneeds.Reconfigu-rability is the ability to meet changing demands[2,3].
The ability to quickly respond to marketÕs changes, called agility,has been recognid as a key ele
ment in the success and survival of enterpris in todayÕs market.In order to keep up with rapid change,enterpris need to change traditional management in this hot competition. Through dynamic alliance,enterpris exert predomi-nance themlves,cooperate faithfully with each other, and compete jointly so as to meet the needs of the fluctuating market,andfinally achieve the goal of win-win[2,3].So how to improve agility in the supply chain, namelyflexibility and reconfigurability,is one of the important factors to win against the competition.
Supply chain management(SCM)is an approach to satisfy the demands of customers for products and r-vices via integrated management in the whole business process from raw material procurement to the product or rvice delivery to customers.In[4],M.S.Fox et al. describe the goals and architecture of integrated supply chain management system(ISCM).In this system,each agent performs one or more supply chain management functions,and coordinates its decisions with other rele-vant agents.ISCM provides an approach to the real time
Int J Adv Manuf Technol(2004)23:197–203 DOI10.1007/s00170-003-1626-x
P.Lou(&)ÆZ.Zhou
Room107,D8Engineering Rearch Center of Numerical Control System,
School of Mechanical Science&Engineering, Huazhong University of Science&Technology, 430074Wuhan,Hubei,P.R.China
E-mail:louping_
Y.-P.ChenÆW.Ai
School of Mechanical Science and Engineering, Huazhong University of Science and Technology, 430074Wuhan,Hubei,P.R.China
performance of supply chain function.The integration of multi-agent technology and constraint network for solving the supply chain management problem is pro-pod[6].In[7],Yan et al.develop a multi-agent-bad negotiation support system for distributed electric power transmission cost allocation bad on the networkflow model and knowledge query&manipulation language (KQML).A KQML bad multi-agent coordination language was propod in[8,9]for distributed and dy-namic supply chain management.However,the coordi-nation mechanisms have not been formally addresd in a multi-agent-bad supply chain.In most industries, marketing is becoming more globalid,and the whole business process is being implemented into a complex network of supply chains.Each enterpri or business unit in the SCM reprents an independent entity with conflicting
and competing product requirements and may posss localid information relevant to their interests.Being aware of this independence,enterpris are regarded as autonomous agents that can decide how to deploy resources under their control to rve their interests.
This paperfirst introduces concepts and characteris-tics of agile supply chains and emphasis the impor-tance of coordination in supply chain.Then,it prents an architecture of agile supply chain bad on a multi-agent theory and states the agentsÕfunctions and responsibilities.Finally,it prents a CBR contract net protocol for coordination and the correlative algorithm for task allocation in multi-agent-bad agile supply chains.
2Agile supply chain
A supply chain is a network from the topologic structure which is compod of autonomous or mi-autonomous enterpris.The enterpris all work together for pro-curement,production,delivery,and so on[10].There is a main enterpri in the supply chain that is responsible for configuring the supply chain according to the de-mand information and for achieving supply chain value using fundflow,materialflow and informationflow as mediums.There are three discontinuous buffers to make the materialflowfluently and satisfy the change in the demand.On the one hand,as every enter
pri manages inventory independently,plenty of funds are wasted.As the demand information moves up-stream,the forecast is inaccurate and the respond to the change in demand is slow[11].Accordingly,the key method for competi-tiveness is improving and optimising supply chain management to achieve integrated,automated,and agile supply chain management and to cut costs in the supply chain.
To optimi supply chain management and coordi-nate the process for materialflow,fundflow and informationflow,it is necessary to make materialflow fluent,quickly fund turnover and keep information integrated.Prompt reconfiguration and coordination is an important characteristic of agile supply chain according to dynamic alliance compositing and de-compositing(enterpri reconfiguration).Agile supply chain management can improve enterpri reconfiguring agility.The agile supply chain breaks through the tra-ditional line-style organizational structure.With net-work technology an enterpri group is formed by a cooperative relationship which includes an enterpri business centre,a production design centre,a supplier,a distribution centre,a bank,a decision-making centre, etc.It reduces the lead time to the market to satisfy customer demand.
Agile supply chain without temporal and spatial limits promptly expands the enterpri scale,marketing share and resource by allied enterpri.So,a key factor of the agile supply chain is t
o integrate heterogeneous information systems adopted in various enterpris.The integration information system can provide marketing information and supplier details.Feasible inventory, quantity and cycle of replenished stock,delivery,etc.is designed using the shared information.
It is evident that agile supply chain is a typical distributed system.A multi-agent system(MAS)which is characterid byflexibility and adaptability is suit-able for an open and dynamic environment.Thus MAS is a good method for agile supply chain man-agement.
3The concept of agents and MAS
Some people define an agent as any piece of software or object which can perform a specific given task.Prently the prevailing opinion is that an agent must exhibit three important general characteristics:autonomy,adapta-tion,and cooperation[8,12,13].Autonomy means that agents have their own agenda of goals and exhibit goal-directed behaviour.Agents are not simply reactive,but can be pro-active and take initiatives as they deem appropriate.Adaptation implies that agents are capable of adapting to the environment,which includes other agents and human urs,and can learn from the expe-rience in order to improve themlves in a changing environment.Cooperation and coordination between agents are probably the most important feature of MAS. Unlike tho stand-al
one agents,agents in a MAS col-laborate with each other to achieve common goals.In other words,the agents share information,knowledge, and tasks among themlves.The intelligence of MAS is not only reflected by the experti of individual agents but also exhibited by the emerged collective behaviour beyond individual agents.Of cour various agents have different functions,but some functions are needed for each agent.A generic structure of agents that includes two parts is prented:agent kernel and function mod-ule.Figure1exhibits the generic structure of agents which is a plug-in model.
In Fig.1,the generic agent includes the following components:
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The mailbox handles communication between one agent and the other agents.
The message handler process incoming message from the mailbox,orders them according to priority level,and dispatches them to the relevant components of the agent.
The coordination engine makes decisions concerning the agent Õs how they should be pursued,when to abandon them,etc.,and nds the accepted tasks to the planner/scheduler.It is also
responsible for coordi-nating the agents Õinteractions with other agents using coordination protocols and strategies.
The planner and scheduler plans the agent Õs tasks on the basis of decisions made by the coordination engine and on resources and task specifications available to the agent.If not,a message is nt to the coordination en-gine for finding extra resources.
The blackboard provides a shared work area for exchanging information,data,and knowledge among function modules.Every function module is an inde-pendent entity.The function modules execute con-currently by the control of planner/scheduler and collaborate through the blackboard.
The acquaintance databa describes one agent Õs relationships with other agents in the society,and its beliefs about the capabilities of tho agents.The coor-dination engine us information contained in this databa when making collaborative arrangements with other agents.
The resource databa rerves a list of resources (referred to in this paper as facts)that are owned by and available to the agent.The resource databa also sup-ports a direct interface to external systems,which allows the interface to dynamically link and utili a proprie-tary databa.
The ontology databa stores the logical definition of each fact type—its legal attributes,the range of legal values for each attribute,any constraints between
attribute values,and any relationship between the attributes of that fact and other facts.
The task/plan databa provides logical descriptions of planning operators (or tasks)known to the agent.
4Multi-agent-bad agile supply chain management Multi-agent-bad agile supply chain management per-forms many functions in a tightly coordinated manner.Agents organi supply chain networks dynamically by coordination according to a changing hange rates go up and down unpredictably,customers change or cancel orders,materials do not arrive on time,production facilities fail,etc.[2,14].Each agent performs one or more supply chain functions independently,and each coordinates his action with other agents.Figure 2provides the architecture of multi-agent-bad agile supply chains.There are two types of agents:functional agents and mediator agents.Functional agents plan and/or control activities in the supply chain.Mediator agents play a system coordinator role s by promoting coopera-tion among agents and providing message rvices.Mediator agents dispatch the tasks to the functional agents or other mediator agents,and th
en tho func-tional or mediator agents complete the tasks by coordi-nation.All functional agents coordinate with each other to achieve the goals assigned by mediator agents.The mediator-mediator and mediator-agent communication is asynchronous,and the communication mode can be point-to-point (between two agents),broadcast (one to all agents),or multicast (to a lected group of agents).Messages are formatted in an extended KQML format.The architecture is characterid by organizational hier-archy and team spirit,simplifying the organisational architecture and reducing the time needed to fulfil the task.The rest of this ction briefly describes each of the mediator agents under
development.
Fig.1Generic structures of agents
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–Customer mediator agent:This agent is responsible for acquiring orders from customers,negotiating with customers about prices,due dates,technical advisory,etc.,and handling customer requests for modifying or cancelling respective orders,then nding the order information to a scheduling mediator agent.If a customer request needs to be re-designed,the infor-mation is nt to a design mediator agent,then to a scheduling mediator agent.坐好
–Scheduling mediator agent:This agent is responsible for scheduling and re-scheduling activities in the fac-tory,exploring hypothetical ‘‘what-if’’scenarios for potential new orders,and generating schedules that are nt to the production mediator agent and logis-tics mediator agent.The scheduling agent also acts as a coordinator when infeasible situations ari.It has the capability to explore tradeoffs among the various constraints and goals that exit in the plant.
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–Logistics mediator agent:This agent is responsible for coordinating multi-plans,multiple-supplier,and
the multiple-distribution centre domain of the enterpri to achieve the best possible results in terms of supply chain goals,which include on-time delivery,cost minimisation,etc.It manages the movement of products or materials across the supply chain from the supplier of raw materials to the finished product customer.
–Production mediator agent:This agent performs the order relea and real-time floor control functions as directed by the scheduling mediator agent.It monitors production operation and facilities.If the production operation is abnormal or a machine breaks down,this agent re-arranges the task or re-schedules with the scheduling mediator agent.
–Transportation mediator agent:This agent is responsible for the assignment and scheduling of transportation resources in order to satisfy inter-plant movement specified by the logistics mediator agent.It is able to take into account a variety of
transportation asts and transportation routes in the construction of its schedules.The goal is to nd the right materials on time to the right location as assigned by the logistics mediator agent.
–Inventory mediator agent:There are three invento-ries at the manufacturing site:raw product inven-tory,work-in-process inventory,and finished product inventory.This agent is responsible for managing
the inventories to satisfy production requirements.
–Supplier mediator agent:This agent is responsible for managing supplier information and choosing suppli-ers bad on requests in the production process.
–Design mediator agent:This agent is responsible for developing new goods and for nding the relevant information to the scheduling mediator agent for scheduling,as well as to the customer mediator agent for providing technological advice.
5Coordination in a multi-agent-bad agile supply chain
Coordination has been defined as the process of man-aging dependencies between activities [15].One impor-tant characteristic of an agile supply chain is the ability to reconfigure quickly according to change in the envi-ronment.In order to operate efficiently,functional entities in the supply chain must work in a tightly coordinated manner.The supply chain works as a net-work of cooperating agents,in which each performs one or more supply chain functions,and each coordinates its action with that of other agents [5].Correspondingly,a SCMS transforms to a MAS.In this MAS,agents may join the system and leave it according to coordinating process.With coordination among agents,this MAS achieves the goal of ‘‘the right products in the right quantities (
at the right location)at the right moment at minimal
cost’’.
Fig.2An architecture of multi-agent bad agile supply chain management
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5.1Contract net protocol combined with
ca-bad reasoning
The contract net is a negotiation protocol(CNP)pro-pod by Smith[15].In the CNP,every agent is regarded as a node,such as a manager or a contractor.The manager agent(MA)is responsible for decomposing, announcing,and allocating the task and contractor agent(CA)is responsible for performing the task.This protocol has been widely ud for multi-agent negotia-tion,but it is inefficient.For this reason,contract net protocol is combined with ca-bad reasoning(CBR).
In ca-bad reasoning(CBR),the target ca is defined as problem or instance which is currently being faced,and the ba ca is problem or instance in the databa.CBR arches the ba ca in the databa under the direction of the target ca,and then the ba ca instructs the target ca to solve the problem.This method is efficient.But at the very beginning,it is very difficult to t up a databa which includes all problems solving cas.The cas may be depicted as follows:
C¼\task;MA;taskÀconstraint;agentÀt> Here,MA is task manager.Task-constraint repre-nts various constraint conditions for performing the task,depicted as a vector{c1,c2,c3,...,c m}.Agent-t is a t of performing the task as defined below:
Agent t¼\sub task i;agent id;cost;time;resource>
f g杭州公益中学
task¼[n
i¼1
sub task i
In the supply chain,the same process in which a certain product moves from the manufacturer to the customer is performed iteratively.So,ca-bad rea-soning is very efficient.Conquently,combining con-tract net protocol with CBR could avoid high communicating on load,thus promoting efficiency.The process can be depicted as follows(Fig.3).
5.2The algorithm for task allocation ba
on CBR contract net protocol
There are two types of agents in the supply chain, cooperative and lf-interested agents.Cooperativ
e agents attempt to maximi social welfare,which is the sum of the agents utilities.They are willing to take individual loss in rvice of the good of the society of agents.For example,function agents come from the same enterpri.In truth,the task allocation among cooperative agents is combinational optimisation prob-lem.
Self-interested agents ek to maximi their own profit without caring about the others.In such a ca,an agent is willing to do other agentsÕtasks only for com-pensation[16].Function agents,for example,come from different enterpris.
In the following ction the algorithm for task allo-cation among lf-interested agents bad on CBR contract net protocol will be addresd.Before describ-ing the algorithm,there are some definitions that must be clarified:
Task—A task which is performed by one agent or veral agents together:T=<task,reward,con-straints>,where task is the t of tasks(task={t1,t2,..., t m}),reward is the payoffto the agents that perform the task(reward={r1,r2,...,r m}),and constraints refer to the bounded condition for performing the task(con-straints={c1,c2,...,c n}).
Agent coalition(AC)—A group of agents that per-form task T,described as a t AC={agent i,i=1,2,...,
n}.
Efficiency of agent—Efficiency of an agent i is de-scribed as follows:
E i¼rewardÀcost
ðÞ=costð1Þwhere reward is the payoffto the agent performing task T,and cost refers to that spend on performing the task. If agent i is not awarded the task,then E i=0.
Efficiency of agent coalition—
E coalition¼rewardÀ
X m
i
cost iÀh
!,
X m
i
cost iþh
!
ð2Þwhere reward is the payoffof the agent coalition per-forming task T;cost i refers to that spend on performing task t i;and h is the expen on forming coalition,which is shared by the members of the coalition.If the coalition is not awarded task T,then E coalition<=0.
6Algorithm:
1.After MA accepts the task T=<task,reward,最发达的国家
constraint>(task is decomposable),then it arches the databa.
2.If itfinds a corresponding ca,it assigns the task or
subtask to the related agents according to the ca, and the process is over
3.If no ca is found,then the task T is announced to
all relevant agents(agent i,i=1,2,...n).
4.The relevant agents make bids for the task accord-
ing to their own states and capabilities.The
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bid Fig.3CBR contract net process
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from agent i can be described as follows:Bid i =<agentid i ,T i ,price i ,condition i >,where i ex-press the bidding agent (i =1,2,...,h );agentid i is the exclusive agent identifier;T i is the task t of agent i Õs fulfilment;price i is the recompen of agent i fulfilling the task T i ;and condition i is the constraint conditions for agent i to fulfil the task T i .
5.If [1 i h
&T i then the task T can not be performed.
Otherwi MA makes a complete combination of the agents,namely to form a number of agent coalitions (or agent ts,amounting to N =2h )1).6.First MA deletes tho agent coalitions where no agents are able to satisfy the constraint condition.Next the rest of the coalitions are grouped by the number of agents in coalitions and put into t P (P ={P 1,P 2,...,P h })in order of the minimum re-compen increa of the coalitions,where P i is the t of agent coalitions,including i agents.
7.MA puts the first coalition from each group P i
(i =1,2,...,h )into t L ,and if L is null then it returns to (10),otherwi it calculates the minimum re-compen of each coalition as follows:
Min P
m i
price i ÃT i
s :t :
P h i ¼1T i T
P m i
condition i constrait
Then it arches for the minimal agent coalition AC min from the t L .
8.MA nds the AC min to the relevant agents,namely MA requests that the agent fulfil the task to-gether.The relevant agents calculate the E coalition and E i according to Eqs.1and 2.If
E coalition !max m
i
E i ,then all agents in the AC min
accept the proposal to form a coalition to perform the task T together.MA assigns the task to the AC min ,and the process is over.Otherwi it deletes the AC min from P i and returns to (7).
9.If the relevant agents accept the task or subtask,then MA assigns the task to them.The process is over.If some agents cannot accept the subtask and the stated time is not attained,then it returns to (3),otherwi it returns to (10).
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10.The process is terminated (namely the task cannot
be performed).After all process have been completed,ca-bad maintenance is required to improve the CBR.Thus efficiency is continuously promoted.
6.1An example
–A simple instantiation of a supply chain simulation is prented here and the negotiating process among agents is shown.In this supply chain instantiation,the
transportation mediator agent (TMA)has a transport
task T ,in which it has to deliver the finished product to the customer within 15units of time and must pay 1500monetary units for it,that is T =<t ,1500,15>.Four transport companies can perform task T .Each company is an autonomous agent,that is four agents,agent A,agent B,agent C and agent D.So the TMA announces the task T to the four agents.Then the four agents make a bid for the task T as shown in Table 1.–So the four agents can form 24)1coalitions (e Fig.4),which are put into t P .Cooperation between agents in the coalition requires expen and the ex-pen for forming the coalition increas with the growth of in coalition size.This means that expanding the coalition may be non-beneficial.The expen of each agent in forming a coalition h is 100.First,the coalitions in which no agents can satisfy the constraint conditions are deleted from the t P .The rest of the coalitions are grouped by the number of agents in the coalition and ordered according to the recompen of each group that was incread due to the coalition,namely P 1={B},P 2={{A,B},{A,C},{B,C},{A,D},{B,D}},P 3={{A,B,C},{A,B,D},{B,C,D}},P 4={{A,B,C,D}}.Then the cost and efficiency of coalition {B},{A,C}and {A,B,C}are calculated as follows:Price f A ;B g ¼Min ð800x 1þ1200x 2Þs :t :20
x 1þ12x 2 15x 1þx 2!1x 1!0:x 2!0
Price f A ;B ;C g ¼Min ð800y 1þ1200y 2þ2000y 3Þs :t :20y 1þ12y 2þ5y 3 15y 1þy 2þy 3!1y 1!0:y 2!0;y 3!
Fig.4Agent coalition graph
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Table 1The bids of four agents Agent Id Price Conditions Agent A 80020Agent B 120012Agent C 20005Agent
D
2500
3
202
