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As none of the strategies was satisfactory, it was decided to develop a simple agent platformand agent framework from scratch for .Net. C# was chosen as the implementation language. Itis indeed a modern OO language that has been designed especially for .Net. At the same time,it is close enough to Java so that learning it is a rather short phase.I designed and implemented the whole Agent System, then a big part of the application.2 Agent infrastructure levelThe infrastructure enables agents to find each other and communicate by exchangingmessages. The application can involve a number of agents that grows with the number ofusers and resources used. There is thus no threshold about the number of agents, which is notacceptable if the application is located on one single machine. For avoiding machine overload,an important characteristics of the infrastructure is that it supports the distribution of agentsamong several machines or hosts.2.1 Agent communicationAll inter-agent communication is achieved through exchanges of messages. Every agent has aunique identifier that is specified in message “addresses” for proper delivery to the recipient.In the ideal case, agents communicate by the mean of dedicated communication language andcontent language. Information is text-based and agents use an interpreter and an ontology forinterpreting it. More heavy-weight data structures like objects are confined inside the agents.Thus agent encapsulation is preserved, only “high-level” information is transmitted andinteroperation between heterogeneous agents is eased.In our case however, developing such a system would conflict with the objective of rapidprototyping. Our agents are homogeneous and are designed specifically for cooperating. Thusa simple communication system has been designed and implemented based on messagesholding a subject and a content object.More precisely, messages are composed of the following data:- The ID of the intended recipient agent for allowing the posting service to deliver themessage;- The ID of the sender agent in order to enable the recipient to send a reply;- A subject for allowing the recipient to identify what the message is about. In otherwords, the subject defines a message category;- The nature of the message: namely notification or request;- Possibly some additional data as a content that the recipient should process. Suchcontent can be any object, thus it is important that it is not part of the sender’s internalstate otherwise it would break the sender’s encapsulation. Alternatively, the contentobject can be passed by value or serialized.2.2 Agent managementFollowing the principles of the experimental FIPA agent management specification, theinfrastructure is composed of 3 services.MSc EMOOSE Thesis – http://www.emn.fr/EMOOSE 39
(1) A Name Server (NS) maps every agent identifier (ID) with the address of the host onwhich the agent runs. Every new agent gets a unique identifier and must register to theNS at initialization time. This allows for the proper delivery of messages to agents.Handling agent IDs and hosts independently is better in terms of design, and it is alsonecessary for enabling agent migration in the future.(2) A Directory Facilitator (DF) enables agents needing a certain service to get the ID ofagents providing the service. In other words, it enables service consumers to findservice producers. A service is any task that an agent can do. The DF brings flexibility(even dynamic) in agent organizations. In contrast, agents could hold simplereferences to the producer agents that they need, but this would not be very suitable ina distributed configuration. For example, if several agents on different hosts are able toprovide the same service, it is better that a consumer queries the local producer or aproducer on the least loaded host.(3) Message Transporters (MTs) are in charge of delivering messages. There is one MTper machine. In the general case, an agent willing to communicate with another agentcreates a message, fills the “recipient” field with the ID of the second agent then poststhe message to the local MT. The MT knows all the local agents so if it finds that therecipient is local, it delivers the message to it. Otherwise, it gets the address of therecipient’s host thanks to the NS and forwards the message to the MT of that host.Computer A (main host)Computer BPostmessageDelivermessageRegister,QueryMTInfrastructureNSDFMTInfrastructureNSDFSharedSharedMSMQ message sendingThe agent infrastructureProxy(Remoting)Proxy(Remoting)The NS and DF must be unique within an agent infrastructure. Therefore, they must beinstantiated on one machine only, which is called the Main Host. The NS and DF can then beaccessed from other hosts using synchronized remote method invocation. This has beenimplemented using the facilities provided in the .Net’s Remoting namespace.In contrast, each host has its own MT. Implementation for remote inter-MT communication isbased on the MSMQ (Microsoft Message Queuing) service. It allows for asynchronousmessage sending with high-level administration facilities. Each agent message is simplyembedded in a MSMQ message.MSc EMOOSE Thesis – http://www.emn.fr/EMOOSE 40
Page 1: Vrije Universiteit Brussel - Belgiu
Page 4 and 5: ContentsAbstract 1Acknowledgements
Page 6 and 7: (4) Table UP_SUP (matches User Prof
Page 9 and 10: content providers’ interpretation
Page 11 and 12: - Active profiling consists in aski
Page 13 and 14: 2 Agents2.1 Overview2.1.1 Definitio
Page 15 and 16: (1) each agent has incomplete infor
Page 17 and 18: MASs need an organization for speci
Page 19 and 20: However, the usefulness of personal
Page 21 and 22: they often provide implementation o
Page 23 and 24: 2.5 Design2.5.1 The DIMA designIn [
Page 25 and 26: 3 MetadataDuring the earlier invest
Page 27 and 28: This requires some agreement and st
Page 29 and 30: 4 PerspectivesRecommender systems m
Page 31 and 32: way Lego blocks should be assembled
Page 33 and 34: usiness intelligence is generated.
Page 35 and 36: important than memory space optimiz
Page 37 and 38: The graph is then formatted to be v
Page 39: Chapter 4: Implementation1 Implemen
Page 43 and 44: the agent terminates, the thread is
Page 45 and 46: 4 Application level4.1 OverviewThe
Page 47 and 48: 4.3 User Agent MakerThis agent has
Page 49 and 50: Thus the profile, node and link cla
Page 51 and 52: BIProviderR : Provide_Business_Inte
Page 53 and 54: to enable users to explicitly speci
Page 55 and 56: ConclusionA “minimalist” approa
Page 57 and 58: Appendix A: Addendum onIndustrial I
Page 59 and 60: Appendix B: SQL Tables Design1 Tabl
Page 61 and 62: Appendix C: Conference PaperA paper
Page 63 and 64: very large repositories of learning
Page 65 and 66: popularity of the link (the bigger
Page 67 and 68: Appendix D: Source Code1 Agent infr
Page 69 and 70: public static bool ProcessIsMainHos
Page 71 and 72: string path = MakePath(".", Middlew
Page 73 and 74: System.Messaging.MessageQueue queue
Page 75 and 76: public static NameServer GetNS(){if
Page 77 and 78: }}}table[agentId] = address;}}/// /
Page 79 and 80: ****** NON-STATIC PART ******// Tab
Page 82 and 83: }}}return (AgentId) first;using Sys
Page 85 and 86: {}return Subject.GetHashCode() + Na
Page 87 and 88: name in order to allow for the retr
Page 89 and 90: }// Start agent's main Thread.Threa
Page 91 and 92:
}DirectoryFacilitator.GetDF().Unreg
Page 93 and 94:
{/// /// Allows for specific conver
Page 95 and 96:
}Monitor.Exit(aLock);public overrid
Page 97 and 98:
Allows for synchronized Message exc
Page 99 and 100:
esource./// /// public string GetMa
Page 101 and 102:
}}private void RunTerminationExamin
Page 103 and 104:
}private Message RequestUACreation(
Page 105 and 106:
}msgQueue.AddFilters(new MessageCat
Page 107 and 108:
Message received: interrupt preterm
Page 109 and 110:
19. Class Architecture.DBManagerAg
Page 111 and 112:
}}connection.Close();/// /// For sa
Page 113 and 114:
using System.Collections;namespace
Page 115 and 116:
namespace Architecture.Profiles{usi
Page 117 and 118:
private UP(DataRow row) : this(newU
Page 119 and 120:
}DataRow[] rows = Row.GetChildRows(
Page 121 and 122:
}adapter.Update(Data);//***********
Page 123 and 124:
internal static readonly string LAS
Page 125 and 126:
}}Row[OCCURRENCES] = Occurrences +
Page 127 and 128:
}get{}return Data.Rows.Find(_name);
Page 129 and 130:
private static SqlDataAdapter adapt
Page 131 and 132:
}foreach (ILink link in links){if (
Page 133 and 134:
}}}private DataRow Row{get{return D
Page 135 and 136:
18. N. Good, et al. Combining colla
Page 137 and 138:
49. D. Derbyshire, et al., Agent-Ba
Page 139:
83. Council for Higher Education Ac
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