Mobile Software Agents Tomasz Müldner

1. Mobile Software AgentsTomasz Müldner October 2, 1998

2. Introduction: History • research on agents was originated by J. McCarthy in the mid-1950’s • the term agent was coined by O.G. Selfridge

3. Introduction: According to some... Agent is an intelligent robot, or “humanoid”, that has emotions, feelings and perceptions, and therefore is concerned with cognitive science, speech acts, etc.

4. Introduction:DAI “...asking the question of what an agent is to a DAI researcher is as embarrassing as the question of what intelligence is for an AI researcher...”Carl Hewitt

5. Introduction: contents of this talk • concentrate on mobile agents • discuss: • communication • security • MALs

6. Agents - what are they?

7. Agents - what are they? a tool to perform client-server computing by transmitting running programs between clients and servers; (White 1994) server

8. Agents - what can they do? • find and filter information • customize views of information (e.g. email) • automate work (respond to events, such as a new version)

9. Agents - what can they do? • make recommendations and perform corporate tasks; e.g. scheduling of meetings • execute diagnostics, e.g. in networks • rapid (re)deployment of applications • active network load balancing

10. Agents - where are they used? • distributed OO • adaptive learning systems • AI, expert systems, genetic algorithms • electronic commerce • collaborative environment • mobile (nomadic) computing

11. Agents - main characteristics

12. Agents - main characteristics • autonomous execution (life); have control over their own actions and may operate without the direct intervention of humans • intelligent (perform domain oriented reasoning)

13. Agents - main characteristics • perceive their environment • adaptive (they learn) • mobile (they move) • persistent (they have their own idea as to how to accomplish a task)

14. Agents - main characteristics • goal oriented (they realize a set of goals) • reactive (or reflexive); they perceive environment and timely and accurately respond to changes that occur in it • active, or proactive: act to accomplish goals (take initiative not only respond to the environment)

15. Intelligent Agents • An intelligent agent has some artificial intelligence; for example based on a set of facts and inference rules • learning agents are adaptive; they can learn themselves about a subject in question by statistically matching subjects of interest with particular people

16. Basic Definitions

17. Basic Definitions • An agent system can create, interpret, execute, transfer and terminate agents • A host can contain several agent systems; each is uniquely identified by its name and address.

18. Basic Definitions • Both, an agent and an agent system have an authority; a person or organization for whom they act • An agent executes in a context, called the place; there may be one or more places within an agent system

19. Basic Definitions • agents have locations (names of their current places) • agents have names (the agent’s authority and identity; a unique value within the scope of the authority)

20. Basic Definitions There are two kinds of agents: • stationary agent is permanently attached to a place; often resource managers, server programs or search engines • mobile agent can move from one place to another

21. Basic Definitions Mobility is not new: • submitting batch jobs on mainframes • perform distributed, real-time processing by executing scripts on networks of mini-computers • databases have been using stored procedures.

22. Agents and DOOP L. Lamport: A distributed system is one in which I cannot get something done because a machine I have never heard of is down.

23. Agents and DOOP: DOOP • distribute applications and use a number of network nodes, rather than a single node • communicate; for example by • messaging (asynchronous) • RPC (synchronous) • CORBA supports language and system independence

24. Agents and DOOP: Efficiency Which is better • to send data to the program • to send a program to the source of data (move the code closer to data)

25. Agents and DOOP: Robustness Agents are better in their ability to recover from server breakdowns or unavailability (disconnected operations)

26. Agents and DOOP: Flexibility • Mobile agents are particularly useful for rapid deployment of applications and dynamic updates of software; a code server can provide required code (this is also called code on demand). • agents can be used for dynamic extensions of server services.

27. Agents and DOOP: Design Designing a client/server architecture requires making all decisions about the communication between the server(s) and the client(s). These decisions are tightly coupled with the underlying problem of specific design and are very difficult or even impossible to change

28. Agents and DOOP: Java • supports rapid deployment of applications, by using a “thin” bootstrap program and code-on-demand approach • objects serialization • local dynamic linking • remote linking that would fetch the code to be linked from a remote site • reflection

29. Agents and DOOP: Java • code servers • applets - no need for installation

30. Agents and DOOP: Java Java does not support mobility

31. Mobile Agent Languages

32. Mobile Agent Languages: Definitions • An executing unit, EU is a single process (or thread) image of execution. EU is always considered in the context of a place, which contains components; either EUs, or resources, such as files. • A MAL is a language designed for distributed systems, which supports EUs migrating between various places.

33. Mobile Agent Languages: Definitions • An EU consists of • a static code segment • a program state: • data space containing accessible resources • execution statecontaining system information such as program counter and return address. • The EU has a distributed state if its data space exists in more than one place.

34. Mobile Agent Languages: Definitions • For an agent to be moved, first it has to be suspended. An entry point is a point where execution of a suspended agent is resumed • Two kinds of resumption: • standard resumption (after “go”) • itinerary; one or more entry points may be explicitly specified.

35. Mobile Agent Languages: Definitions • strong mobility means that the entire code and execution state of EUs can be moved • Strong mobility combined with standard resumption == strong MAL (implies that it must be possible to save the state of the execution, and later, to restore this state)

36. Mobile Agent Languages: Definitions • Strong MALs: • Java with a modified JVM • Tcl with modified interpreter • Scheme (no modifications) • Weak MALs: • aglets

37. Mobile Agent Languages: Dynamic Linking

38. Mobile Agent Languages: Dynamic Linking • Name resolution must be able to bind names to both local and remote entities • remote code dynamic linking: the code downloaded from a remote site and linked with an EU • local resource dynamic linking: arriving EU links with resources available in this place; e.g. link with libraries.

39. Mobile Agent Languages: Dynamic Linking in Java • the standard class loader provides local resource linking and the user defined class loader can support remote code linking • The programmer has a choice of • fully resolving the class, i.e. load the code closure • partially resolving the class, i.e. postpone resolving dependent classes until later time.

40. Mobile Agent Languages: Dynamic Linking in MALs library site provides precompiled code that can be picked up by an agent to use at other sites we consider four kinds of dynamic linking. For each kind, we consider an example of a search on a list of sites, using a search procedure.

41. Mobile Agent Languages: Local only Dynamic Linking All the bindings are voided when a program moves. For our example, search is rebound at every site.

42. Mobile Agent Languages: Code-with-a-reference-is-sticky Dynamic Linking A binding is retained as long as there is at least one reference; otherwise it is garbage-collected. In our example, the first site provides binding which will be retained for remaining sites.

43. Mobile Agent Languages: User-specified-sticky linksDynamic Linking The user specifies the initial binding which is then retained (as long as there is a reference). In our example, the user can specify which version of search should be used for the traversal.

44. Mobile Agent Languages: User-specifiedDynamic Linking Gives the programmer complete control over linking. In our example, the user can specify which version of search should be used for the traversal.

45. Mobile Agent Languages: Communication

46. Mobile Agent Languages: Types ofCommunication • agent to service agent; this is typically a client/ server type of interaction (e.g. based on RPC) • agent to agent; this a peer-to-peer type of interaction and could be supported by messaging • agent to group; this is a group communication (e.g. based on an observer pattern) • user to agent interaction; this a standard human-computer interaction, HCI.

47. Mobile Agent Languages: Types of Communication • agent to service agent and agent to agent are session oriented

48. Security

49. Security:Definitions • a security policy is a set of guidelines describing whether various actions are allowed or not(may also include royalties) • a security policy is static if its guidelines do not depend on external conditions; otherwise it is dynamic. • a security policy may include credentials, or level of trust.

50. Security:Definitions Java Security Manager implements a static security policy, which controls access to resources such as file I/O, network access, and others. There is no provision to limit access to other resources such as CPU cycles.