Patent 06851115 - Software-based architecture for communication and cooperation among distributed electronic agents > Description
A compact disk containing a computer program listing has been provided in duplicate (copy 1 and copy 2 of the compact disk are identical). The computer program listing in the compact disk is incorporated by reference herein. The compact disk contains files with their names, size and date of creation as follow:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to distributed computing environments and the completion of tasks within such environments. In particular, the present invention teaches a variety of software-based architectures for communication and cooperation among distributed electronic agents. Certain embodiments teach interagent communication languages enabling client agents to make requests in the form of arbitrarily complex goal expressions that are solved through facilitation by a facilitator agent.
Context and Motivation for Distributed Software Systems
The evolution of models for the design and construction of distributed software systems is being driven forward by several closely interrelated trends: the adoption of a networked computing model, rapidly rising expectations for smarter, longer-lived, more autonomous software applications and an ever increasing demand for more accessible and intuitive user interfaces.
FIG. 1illustrates a networked computing model 100 having a plurality of client and server computer systems 120 and 122 coupled together over a physical transport mechanism 140. The adoption of the networked computing model 100 has lead to a greatly increased reliance on distributed sites for both data and processing resources. Systems such as the networked computing model 100 are based upon at least one physical transport mechanism 140 coupling the multiple computer systems 120 and 122 to support the transfer of information between these computers.
Some of these computers basically support using the network and are known as client computers (clients). Some of these computers provide resource to other computers and are known as server computers (servers). The servers 122 can vary greatly in the resources they possess, access they provide and services made available to other computers across a network. Servers may service other servers as well as clients.
The Internet is a computing system based upon this network computing model. The Internet is continually growing, stimulating a paradigm shift for computing away from requiring all relevant data and programs to reside on the user\'s desktop machine. The data now routinely accessed from computers spread around the world has become increasingly rich in format, comprising multimedia documents, and audio and video streams. With the popularization of programming languages such as JAVA, data transported between local and remote machines may also include programs that can be downloaded and executed on the local machine. There is an ever increasing reliance on networked computing, necessitating software design approaches that allow for flexible composition of distributed processing elements in a dynamically changing and relatively unstable environment.
In an increasing variety of domains, application designers and users are coming to expect the deployment of smarter, longer-lived, more autonomous, software applications. Push technology, persistent monitoring of information sources, and the maintenance of user models, allowing for personalized responses and sharing of preferences, are examples of the simplest manifestations of this trend. Commercial enterprises are introducing significantly more advanced approaches, in many cases employing recent research results from artificial intelligence, data mining, machine learning, and other fields.
More than ever before, the increasing complexity of systems, the development of new technologies, and the availability of multimedia material and environments are creating a demand for more accessible and intuitive user interfaces. Autonomous, distributed, multi-component systems providing sophisticated services will no longer lend themselves to the familiar â€œdirect manipulationâ€ model of interaction, in which an individual user masters a fixed selection of commands provided by a single application. Ubiquitous computing, in networked environments, has brought about a situation in which the typical user of many software services is likely to be a non-expert, who may access a given service infrequently or only a few times. Accommodating such usage patterns calls for new approaches, fortunately, input modalities now becoming widely available, such as speech recognition and pen-based handwriting/gesture recognition, and the ability to manage the presentation of systems\' responses by using multiple media provide an opportunity to fashion a style of human-computer interaction that draws much more heavily on our experience with human-human interactions.
2. Prior Related Art
Existing approaches and technologies for distributed computing include to distributed objects, mobile objects, blackboard-style architectures, and agent-based software engineering.
The Distributed Object Approach
Object-oriented languages, such as C++ or JAVA, provide significant advances over standard procedural languages with respect to the reusability and modularity of code: encapsulation, inheritance and polymorhpism. Encapsulation encourages the creation of library interfaces that minimize dependencies on underlying algorithms or data structures. Changes to programming internals can be made at a later date with requiring modifications to the code that uses the library. Inheritance permits the extension and modification of a library of routines and data without requiring source code to the original library. Polymorphism allows one body of code to work on an arbitrary number of data types. For the sake of simplicity traditional objects may be seen to contain both methods and data. Methods provide the mechanisms by which the internal state of an object may be modified or by which communication may occur with another object or by which the instantiation or removal of objects may be directed.
With reference to
FIG. 2, a distributed object technology based around an Object Request Broker will now be described. Whereas â€œstandardâ€ object-oriented programming (OOP) languages can be used to build monolithic programs out of many object building blocks, distributed object technologies (DOOP) allow the creation of programs whose components may be spread across multiple machines. As shown in
FIG. 2, an object system 200 includes client objects 210 and server objects 220. To implement a client-server relationship between objects, the distributed object system 200 uses a registry mechanism (CORBA\'s registry is called an object Request Broker, or ORB) 230 to store the interface descriptions of available objects. Through the services of the ORB 230, a client can transparently invoke a method on a remote server object. The ORB 230 is then responsible for finding the object 220 that can implement the request, passing it the parameters, invoking its method, and returning the results. In the most sophisticated systems, the client 210 does not have to be aware of where the object is located, its programming language, its operating system, or any other system aspects that are not part of the server object\'s interface.
Although distributed objects offer a powerful paradigm for creating networked applications, certain aspects of the approach are not perfectly tailored to the constantly changing environment of the Internet. A major restriction of the DOOP approach is that the interactions among objects are fixed through explicitly coded instructions by the application developer. It is often difficult to reuse an object in a new application without bringing along all its inherent dependencies on other objects (embedded interface definitions and explicit method calls). Another restriction of the DOOP approach is the result of its reliance on a remote procedure call (RPC) style of communication. Although easy to debug, this single thread of execution model does not facilitate programming to exploit the potential for parallel computation that one would expect in a distributed environment. In addition, RPC uses a blocking (synchronous) scheme that does not scale well for high-volume transactions.
Mobile objects, sometimes called mobile agents, are bits of code that can move to another execution site (presumably on a different machine) under their own programmatic control, where they can then interact with the local environment. For certain types of problems, the mobile object paradigm offers advantages over more traditional distributed object approaches. These advantages include network bandwidth and parallelism. Network bandwidth advantages exist for some database queries or electronic commerce applications, where it is more efficient to perform tests on data by bringing the tests to the data than by bringing large amounts of data to the testing program. Parallelism advantages include situations in which mobile agents can be spawned in parallel to accomplish many tasks at once.
Some of the disadvantages and inconveniences of the mobile agent approach include the programmatic specificity of the agent interactions, lack of coordination support between participant agents and execution environment irregularities regarding specific programming languages supported by host processors upon which agents reside. In a fashion similar to that of DOOP programming, an agent developer must programmatically specify where to go and how to interact with the target environment. There is generally little coordination support to encourage interactions among multiple (mobile) participants. Agents must be written in the programming language supported by the execution environment, whereas many other distributed technologies support heterogeneous communities of components, written in diverse programming languages.
Blackboard architectures typically allow multiple processes to communicate by reading and writing tuples from a global data store. Each process can watch for items of interest, perform computations based on the state of the blackboard, and then add partial results or queries that other processes can consider. Blackboard architectures provide a flexible framework for problem solving by a dynamic community of distributed processes. A blackboard architecture provides one solution to eliminating the tightly bound interaction links that some of the other distributed technologies require during interprocess communication. This advantage can also be a disadvantage: although a programmer does not need to refer to a specific process during computation, the framework does not provide programmatic control for doing so in cases where this would be practical.
Agent-based Software Engineering
Several research communities have approached distributed computing by casting it as a problem of modeling communication and cooperation among autonomous entities, or agents. Effective communication among independent agents requires four components: (1) a transport mechanism carrying messages in an asynchronous fashion, (2) an interaction protocol defining various types of communication interchange and their social implications (for instance, a response is expected of a question), (3) a content language permitting the expression and interpretation of utterances, and (4) an agreed-upon set of shared vocabulary and meaning for concepts often called an ontology). Such mechanisms permit a much richer style of interaction among participants than can be expressed using a distributed object\'s RPC model or a blackboard architecture\'s centralized exchange approach.
Agent-based systems have shown much promise for flexible, fault-tolerant, distributed problem solving. Several agent-based projects have helped to evolve the notion of facilitation. However, existing agent-based technologies and architectures are typically very limited in the extent to which agents can specify complex goals or influence the strategies used by the facilitator. Further, such prior systems are not sufficiently attuned to the importance of integrating human agents (i.e., users) through natural language and other human-oriented user interface technologies.
The initial version of SRI International\'s Open Agent Architectureâ„¢ (â€œOAAÂ®â€ ) technology provided only a very limited mechanism for dealing with compound goals. Fixed formats were available for specifying a flat list of either conjoined (AND) sub-goals or disjoined (OR) sub-goals; in both cases, parallel goal solving was hard-wired in, and only a single set of parameters for the entire list could be specified. More complex goal expressions involving (for example) combinations of different boolean connectors, nested expressions, or conditionally interdependent (â€œIF . . . THENâ€ ) goals were not supported. Further, system scalability was not adequately addressed in this prior work.
SUMMARY OF INVENTION
A first embodiment of the present invention discloses a highly flexible, software-based architecture for constructing distributed systems. The architecture supports cooperative task completion by flexible, dynamic configurations of autonomous electronic agents. Communication and cooperation between agents are brokered by one or more facilitators, which are responsible for matching requests, from users and agents, with descriptions of the capabilities of other agents. It is not generally required that a user or agent know the identities, locations, or number of other agents involved in satisfying a request, and relatively minimal effort is involved in incorporating new agents and â€œwrappingâ€ legacy applications. Extreme flexibility is achieved through an architecture organized around the declaration of capabilities by service-providing agents, the construction of arbitrarily complex goals by users and service-requesting agents, and the role of facilitators in delegating and coordinating the satisfaction of these goals, subject to advice and constraints that may accompany them. Additional mechanisms and features include facilities for creating and maintaining shared repositories of data; the use of triggers to instantiate commitments within and between agents; agent-based provision of multi-modal user interfaces, including natural language; and built-in support for including the user as a privileged member of the agent community. Specific embodiments providing enhanced scalability are also described.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1depicts a networked computing model;
FIG. 2depicts a distributed object technology based around an Object Resource Broker;
Examples of the Invention
FIG. 3depicts a distributed agent system based around a facilitator agent;
FIG. 4presents a structure typical of one small system of the present invention;
FIG. 5depicts an Automated Office system implemented in accordance with an example embodiment of the present invention supporting a mobile user with a laptop computer and a telephone;
FIG. 6schematically depicts an Automated Office system implemented as a network of agents in accordance with a preferred embodiment of the present invention;
FIG. 7schematically shows data structures internal to a facilitator in accordance with a preferred embodiment of the present invention;
FIG. 8depicts operations involved in instantiating a client agent with its parent facilitator in accordance with a preferred embodiment of the present invention;
FIG. 9depicts operations involved in a client agent initiating a service request and receiving the response to that service request in accordance with a certain preferred embodiment of the present invention;
FIG. 10depicts operations involved in a client agent responding to a service request in accordance with another preferable embodiment of the present invention;
FIG. 11depicts operations involved in a facilitator agent response to a service request in accordance with a preferred embodiment of the present invention;
FIG. 12depicts an Open Agent Architectureâ„¢ based system of agents implementing a unified messaging application in accordance with a preferred embodiment of the present invention;
FIG. 13depicts a map oriented graphical user interface display as might be displayed by a multi-modal map application in accordance with a preferred embodiment of the present invention;
FIG. 14depicts a peer to peer multiple facilitator based agent system supporting distributed agents in accordance with a preferred embodiment of the present invention;
FIG. 15depicts a multiple facilitator agent system supporting at least a limited form of a hierarchy of facilitators in accordance with a preferred embodiment of the present invention; and
FIG. 16depicts a replicated facilitator architecture in accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3illustrates a distributed agent system 300 in accordance with one embodiment of the present invention. The agent system 300 includes a facilitator agent 310 and a plurality of agents 320. The illustration of
FIG. 3provides a high level view of one simple system structure contemplated by the present invention. The facilitator agent 310 is in essence the â€œparentâ€ facilitator for its â€œchildrenâ€ agents 320. The agents 320 forward service requests to the facilitator agent 310. The facilitator agent 310 interprets these requests, organizing a set of goals which are then delegated to appropriate agents for task completion.
The system 300 of
FIG. 3can be expanded upon and modified in a variety of ways consistent with the present invention. For example, the agent system 300 can be distributed across a computer network such as that illustrated in FIG. 1. The facilitator agent 310 may itself have its functionality distributed across several different computing platforms. The agents 320 may engage in interagent communication (also called peer to peer communications). Several different systems 300 may be coupled together for enhanced performance. These and a variety of other structural configurations are described below in greater detail.
FIG. 4presents the structure typical of a small system 400 in one embodiment of the present invention, showing user interface agents 408, several application agents 404 and meta-agents 406, the system 400 organized as a community of peers by their common relationship to a facilitator agent 402. As will be appreciated,
FIG. 4places more structure upon the system 400 than shown in
FIG. 3, but both are valid representations of structures of the present invention. The facilitator 402 is a specialized server agent that is responsible for coordinating agent communications and cooperative problem-solving. The facilitator 402 may also provide a global data store for its client agents, allowing them to adopt a blackboard style of interaction. Note that certain advantages are found in utilizing two or more facilitator agents within the system 400. For example, larger systems can be assembled from multiple facilitator/client groups, each having the sort of structure shown in FIG. 4. All agents that are not facilitators are referred to herein generically as client agentsâ€”so called because each acts (in some respects) as a client of some facilitator, which provides communication and other essential services for the client.
The variety of possible client agents is essentially unlimited. Some typical categories of client agents would include application agents 404, meta-agents 406, and user interface agents 408, as depicted in FIG. 4. Application agents 404 denote specialists that provide a collection of services of a particular sort. These services could be domain-independent technologies (such as speech recognition, natural language processing 410, email, and some forms of data retrieval and data mining) or user-specific or domain-specific (such as a travel planning and reservations agent). Application agents may be based on legacy applications or libraries, in which case the agent may be little more than a wrapper that calls a pre-existing API 412, for example. Meta-agents 406 are agents whose role is to assist the facilitator agent 402 in coordinating the activities of other agents. While the facilitator 402 possesses domain-independent coordination strategies, meta-agents 406 can augment these by using domain- and application-specific knowledge or reasoning (including but not limited to rules, learning algorithms and planning).
With further reference to
FIG. 4, user interface agents 408 can play an extremely important and interesting role in certain embodiments of the present invention. By way of explanation, in some systems, a user interface agent can be implemented as a collection of â€œmicro-agentsâ€ , each monitoring a different input modality (point-and-click, handwriting, pen gestures, speech), and collaborating to produce the best interpretation of the current inputs. These micro-agents are depicted in
FIG. 4, for example, as Modality Agents 414. While describing such subcategories of client agents is useful for purposes of illustration and understanding, they need not be formally distinguished within the system in preferred implementations of the present invention.
The operation of one preferred embodiment of the present invention will be discussed in greater detail below, but may be briefly outlined as follows. When invoked, a client agent makes a connection to a facilitator, which is known as its parent facilitator. These connections are depicted as a double headed arrow between the client agent and the facilitator agent in
FIGS. 3 and 4, for example. Upon connection, an agent registers with its parent facilitator a specification of the capabilities and services it can provide. For example, a natural language agent may register the characteristics of its available natural language vocabulary. (For more details regarding client agent connections, see the discussion of
FIG. 8below.) Later during task completion, when a facilitator determines that the registered services 416 of one of its client agents will help satisfy a goal, the facilitator sends that client a request expressed in the Interagent Communication Language (ICL) 418. (See
FIG. 11below for a more detailed discussion of the facilitator operations involved.) The agent parses this request, processes it, and returns answers or status reports to the facilitator. In processing a request, the client agent can make use of a variety of infrastructure capabilities provided in the preferred embodiment. For example, the client agent can use ICL 418 to request services of other agents, set triggers, and read or write shared data on the facilitator or other client agents that maintain shared data. (See the discussion of
FIGS. 9-11below for a more detailed discussion of request processing.)
The functionality of each client agent are made available to the agent community through registration of the client agent\'s capabilities with a facilitator 402. A software â€œwrapperâ€ essentially surrounds the underlying application program performing the services offered by each client. The common infrastructure for constructing agents is preferably supplied by an agent library. The agent library is preferably accessible in the runtime environment of several different programming languages. The agent library preferably minimizes the effort required to construct a new system and maximizes the ease with which legacy systems can be â€œwrappedâ€ and made compatible with the agent-based architecture of the present invention.
By way of further illustration, a representative application is now briefly presented with reference to
FIGS. 5 and 6. In the Automated Office system depicted in
FIG. 5, a mobile user with a telephone and a laptop computer can access and task commercial applications such as calendars, databases, and email systems running back at the office. A user interface (UI) agent 408, shown in
FIG. 6, runs on the user\'s local laptop and is responsible for accepting user input, sending requests to the facilitator 402 for delegation to appropriate agents, and displaying the results of the distributed computation. The user may interact directly with a specific remote application by clicking on active areas in the interface, calling up a form or window for that application, and making queries with standard interface dialog mechanisms. Conversely, a user may express a task to be executed by using typed, handwritten, or spoken (over the telephone) English sentences, without explicitly specifying which agent or agents should perform the task.
For instance, if the question â€œWhat is my schedule?â€ is written 420 in the user interface 408, this request will be sent 422 by the UI 408 to the facilitator 402, which in turn will ask 424 a natural language (NL) agent 426 to translate the query into JCL 18. To accomplish this task, the NL agent 426 may itself need to make requests of the agent community to resolve unknown words such as â€œmeâ€ 428 (the UI agent 408 can respond 430 with the name of the current user) or â€œscheduleâ€ 432 (the calendar agent 434 defines this word 436). The resulting ICL expression is then routed by the facilitator 402 to appropriate agents (in this case, the calendar agent 434) to execute the request. Results are sent back 438 to the UI agent 408 for display.
The spoken request â€œWhen mail arrives for me about security, notify me immediately.â€ produces a slightly more complex example involving communication among all agents in the system. After translation into ICL as described above, the facilitator installs a trigger 440 on the mail agent 442 to look for new messages about security. When one such message does arrive in its mail spool, the trigger fires, and the facilitator matches the action part of the trigger to capabilities published by the notification agent 446. The notification agent 446 is a meta-agent, as it makes use of rules concerning the optimal use of different output modalities (email, fax, speech generation over the telephone) plus information about an individual user\'s preferences 448 to determine the best way of relaying a message through available media transfer application agents. After some competitive parallelism to locate the user (the calendar agent 434 and database agent 450 may have different guesses as to where to find the user) and some cooperative parallelism to produce required information (telephone number of location, user password, and an audio file containing a text-to-speech representation of the email message), a telephone agent 452 calls the user, verifying its identity through touchtones, and then play the message.
The above example illustrates a number of inventive features. As new agents connect to the facilitator, registering capability specifications and natural language vocabulary, what the user can say and do dynamically changes; in other words, the ICL is dynamically expandable. For example, adding a calendar agent to the system in the previous example and registering its capabilities enables users to ask natural language questions about their â€œscheduleâ€ without any need to revise code for the facilitator, the natural language agents, or any other client agents. In addition, the interpretation and execution of a task is a distributed process, with no single agent defining the set of possible inputs to the system. Further, a single request can produce cooperation and flexible communication among many agents, written in different programming languages and spread across multiple machines.
Design Philosophy and Considerations
One preferred embodiment provides an integration mechanism for heterogeneous applications in a distributed infrastructure, incorporating some of the dynamism and extensibility of blackboard approaches, the efficiency associated with mobile objects, plus the rich and complex interactions of communicating agents. Design goals for preferred embodiments of the present invention may be categorized under the general headings of interoperation and cooperation, user interfaces, and software engineering. These design goals are not absolute requirements, nor will they necessarily be satisfied by all embodiments of the present invention, but rather simply reflect the inventor\'s currently preferred design philosophy.
Versatile Mechanisms of Interoperation and Cooperation
Interoperation refers to the ability of distributed software componentsâ€”agentsâ€”to communicate meaningfully. While every system-building framework must provide mechanisms of interoperation at some level of granularity, agent-based frameworks face important new challenges in this area. This is true primarily because autonomy, the hallmark of individual agents, necessitates greater flexibility in interactions within communities of agents. Coordination refers to the mechanisms by which a community of agents is able to work together productively on some task. In these areas, the goals for our framework are to provide flexibility in assembling communities of autonomous service providers, provide flexibility in structuring cooperative interactions, impose the right amount of structure, as well as include legacy and â€œowned-elsewhereâ€ applications.
Provide flexibility in assembling communities of autonomous service providersâ€”both at development time and at runtime. Agents that conform to the linguistic and ontological requirements for effective communication should be able to participate in an agent community, in various combinations, with minimal or near minimal prerequisite knowledge of the characteristics of the other players. Agents with duplicate and overlapping capabilities should be able to coexist within the same community, with the system making optimal or near optimal use of the redundancy.
Provide flexibility in structuring cooperative interactions among the members of a community of agents. A framework preferably provides an economical mechanism for setting up a variety of interaction patterns among agents, without requiring an inordinate amount of complexity or infrastructure within the individual agents. The provision of a service should be independent or minimally dependent upon a particular configuration of agents.
Impose the right amount of structure on individual agents. Different approaches to the construction of multi-agent systems impose different requirements on the individual agents. For example, because KQML is neutral as to the content of messages, it imposes minimal structural requirements on individual agents. On the other hand, the BDI paradigm tends to impose much more demanding requirements, by making assumptions about the nature of the programming elements that are meaningful to individual agents. Preferred embodiments of the present invention should fall somewhere between the two, providing a rich set of interoperation and coordination capabilities, without precluding any of the software engineering goals defined below.
Include legacy and â€œowned-elsewhereâ€ applications. Whereas legacy usually implies reuse of an established system fully controlled by the agent-based system developer, owned-elsewhere refers to applications to which the developer has partial access, but no control. Examples of owned-elsewhere applications include data sources and services available on the World Wide Web, via simple form-based interfaces, and applications used cooperatively within a virtual enterprise, which remain the properties of separate corporate entities. Both classes of application must preferably be able to interoperate, more or less as full-fledged members of the agent community, without requiring an overwhelming integration effort.
Human-Oriented User Interfaces
Systems composed of multiple distributed components, and possibly dynamic configurations of components, require the crafting of intuitive user interfaces to provide conceptually natural interaction mechanisms, treat users as privileged members of the agent community and support collaboration.
Provide conceptually natural interaction mechanisms with multiple distributed components. When there are numerous disparate agents, and/or complex tasks implemented by the system, the user should be able to express requests without having detailed knowledge of the individual agents. With speech recognition, handwriting recognition, and natural language technologies becoming more mature, agent architectures should preferably support these forms of input playing increased roles in the tasking of agent communities.
Preferably treat users as privileged members of the agent community by providing an appropriate level of task specification within software agents, and reusable translation mechanisms between this level and the level of human requests, supporting constructs that seamlessly incorporate interactions between both human-interface and software types of agents.
Preferably support collaboration (simultaneous work over shared data and processing resources) between users and agents.
Realistic Software Engineering Requirements
System-building frameworks should preferably address the practical concerns of real-world applications by the specification of requirements which preferably include: Minimize the effort required to create new agents, and to wrap existing applications. Encourage reuse, both of domain-independent and domain-specific components. The concept of agent orientation, like that of object orientation, provides a natural conceptual framework for reuse, so long as mechanisms for encapsulation and interaction are structured appropriately. Support lightweight mobile platforms. Such platforms should be able to serve as hosts for agents, without requiring the installation of a massive environment. It should also be possible to construct individual agents that are relatively small and modest in their processing requirements. Minimize platform and language barriers. Creation of new agents, as well as wrapping of existing applications, should not require the adoption of a new language or environment.
Mechanisms of Cooperation
Cooperation among agents in accordance with the present invention is preferably achieved via messages expressed in a common language, ICL. Cooperation among agent is further preferably structured around a three-part approach: providers of services register capabilities specifications with a facilitator, requesters of services construct goals and relay them to a facilitator, and facilitators coordinate the efforts of the appropriate service providers in satisfying these goals.
The Interagent Communication Language (ICL)
Interagent Communication Language (â€œICLâ€ ) 418 refers to an interface, communication, and task coordination language preferably shared by all agents, regardless of what platform they run on or what computer language they are programmed in. ICL may be used by an agent to task itself or some subset of the agent community. Preferably, ICL allows agents to specify explicit control parameters while simultaneously supporting expression of goals in an underspecified, loosely constrained manner. In a further preferred embodiment, agents employ ICL to perform queries, execute actions, exchange information, set triggers, and manipulate data in the agent community.
In a further preferred embodiment, a program element expressed in ICL is the event. The activities of every agent, as well as communications between agents, are preferably structured around the transmission and handling of events. In communications, events preferably serve as messages between agents; in regulating the activities of individual agents, they may preferably be thought of as goals to be satisfied. Each event preferably has a type, a set of parameters, and content. For example, the agent library procedure oaa_Solve can be used by an agent to request services of other agents. A call to oaa_Solve, within the code of agent A, results in an event having the form
- ev_post_solve(Goal, Params)
going from A to the facilitator, where ev_post_solve is the type, Goal is the content, and Params is a list of parameters. The allowable content and parameters preferably vary according to the type of the event.
- ev_post_solve(Goal, Params)
The ICL preferably includes a layer of conversational protocol and a content layer. The conversational layer of ICL is defined by the event types, together with the parameter lists associated with certain of these event types. The content layer consists of the specific goals, triggers, and data elements that may be embedded within various events.
The ICL conversational protocol is preferably specified using an orthogonal, parameterized approach, where the conversational aspects of each element of an interagent conversation are represented by a selection of an event type and a selection of values from at least one orthogonal set of parameters. This approach offers greater expressiveness than an approach based solely on a fixed selection of speech acts, such as embodied in KQML. For example, in KQML, a request to satisfy a query can employ either of the performatives ask_all or ask_one. In ICL, on the other hand, this type of request preferably is expressed by the event type evost solve, together with the solution_limit(N) parameterâ€”where N can be any positive integer. (A request for all solutions is indicated by the omission of the solution_limit parameter.) The request can also be accompanied by other parameters, which combine to further refine its semantics. In KQML, then, this example forces one to choose between two possible conversational options, neither of which may be precisely what is desired. In either case, the performative chosen is a single value that must capture the entire conversational characterization of the communication. This requirement raises a difficult challenge for the language designer, to select a set of performatives that provides the desired functionality without becoming unmanageably large. Consequently, the debate over the right set of performatives has consumed much discussion within the KQML community.
The content layer of the ICL preferably supports unification and other features found in logic programming language environments such as PROLOG. In some embodiments, the content layer of the ICL is simply an extension of at least one programming language. For example, the Applicants have found that PROLOG is suitable for implementing and extending into the content layer of the ICL. The agent libraries preferably provide support for constructing, parsing, and manipulating ICL expressions. It is possible to embed content expressed in other languages within an ICL event. However, expressing content in ICL simplifies the facilitator\'s access to the content, as well as the conversational layer, in delegating requests. This gives the facilitator more information about the nature of a request and helps the facilitator decompose compound requests and delegate the sub-requests.
Further, ICL expressions preferably include, in addition to events, at least one of the following: capabilities declarations, requests for services, responses to requests, trigger specifications, and shared data elements. A further preferred embodiment of the present invention incorporates ICL expressions including at least all of the following: events, capabilities declarations, requests for services, responses to requests, trigger specifications, and shared data elements.
Providing Services: Specifying â€œSolvablesâ€
In a preferred embodiment of the present invention, every participating agent defines and publishes a set of capability declarations, expressed in ICL, describing the services that it provides. These declarations establish a high-level interface to the agent. This interface is used by a facilitator in communicating with the agent, and, most important, in delegating service requests (or parts of requests) to the agent. Partly due to the use of PROLOG as a preferred basis for ICL, these capability declarations are referred as solvables. The agent library preferably provides a set of procedures allowing an agent to add, remove, and modify its solvables, which it may preferably do at any time after connecting to its facilitator.
There are preferably at least two major types of solvables: procedure solvables and data solvables. Intuitively, a procedure solvable performs a test or action, whereas a data solvable provides access to a collection of data. For example, in creating an agent for a mail system, procedure solvables might be defined for sending a message to a person, testing whether a message about a particular subject has arrived in the mail queue, or displaying a particular message onscreen. For a database wrapper agent, one might define a distinct data solvable corresponding to each of the relations present in the database. Often, a data solvable is used to provide a shared data store, which may be not only queried, but also updated, by various agents having the required permissions.
There are several primary technical differences between these two types of solvables. First, each procedure solvable must have a handler declared and defined for it, whereas this is preferably not necessary for a data solvable. The handling of requests for a data solvable is preferably provided transparently by the agent library. Second, data solvables are preferably associated with a dynamic collection of facts (or clauses), which may be further preferably modified at runtime, both by the agent providing the solvable, and by other agents (provided they have the required permissions). Third, special features, available for use with data solvables, preferably facilitate maintaining the associated facts. In spite of these differences, it should be noted that the mechanism of use by which an agent requests a service is the same for the two types of solvables.
In one embodiment, a request for one of an agent\'s services normally arrives in the form of an event from the agent\'s facilitator. The appropriate handler then deals with this event. The handler may be coded in whatever fashion is most appropriate, depending on the nature of the task, and the availability of task-specific libraries or legacy code, if any. The only hard requirement is that the handler return an appropriate response to the request, expressed in ICL. Depending on the nature of the request, this response could be an indication of success or failure, or a list of solutions (when the request is a data query).
A solvable preferably has three parts: a goal, a list of parameters, and a list of permissions, which are declared using the format:
- solvable(Goal, Parameters, Permissions)
The goal of a solvable, which syntactically takes the preferable form of an ICL structure, is a logical representation of the service provided by the solvable. (An ICL structure consists of a functor with 0 or more arguments. For example, in the structure a(b,c), â€˜aâ€™ is the functor, and â€˜bâ€™ and â€˜câ€™ the arguments.) As with a PROLOG structure, the goal\'s arguments themselves may preferably be structures.
Various options can be included in the parameter list, to refine the semantics associated with the solvable. The type parameter is preferably used to say whether the solvable is data or procedure. When the type is procedure, another parameter may be used to indicate the handler to be associated with the solvable. Some of the parameters appropriate for a data solvable are mentioned elsewhere in this application. In either case (procedure or data solvable), the private parameter may be preferably used to restrict the use of a solvable to the declaring agent when the agent intends the solvable to be solely for its internal use but wishes to take advantage of the mechanisms in accordance with the present invention to access it, or when the agent wants the solvable to be available to outside agents only at selected times. In support of the latter case, it is preferable for the agent to change the status of a solvable from private to non-private at any time.
The permissions of a solvable provide mechanisms by which an agent may preferably control access to its services allowing the agent to restrict calling and writing of a solvable to itself and/or other selected agents. (Calling means requesting the service encapsulated by a solvable, whereas Writing means modifying the collection of facts associated with a data solvable.) The default permission for every solvable in a further preferred embodiment of the present invention is to be callable by anyone, and for data solvables to be writable by anyone. A solvable\'s permissions can preferably be changed at any time, by the agent providing the solvable.
For example, the solvables of a simple email agent might include:
- solvable(send_message(email, +ToPerson, +Params),
- [type(procedure), callback(send_mail)],
- [ ]
- [type(procedure), callback(send_mail)],
- solvable(last_message(email, âˆ’MessageId),
- [type(data), single_value(true)],
- solvable (get_message (email, +MessageId, âˆ’Msg),
- [type(procedure), callback(get_mail)], [ ])
- solvable(send_message(email, +ToPerson, +Params),
The symbols â€˜+â€™ and â€˜âˆ’â€™, indicating input and output arguments, are at present used only for purposes of documentation. Most parameters and permissions have default values, and specifications of default values may be omitted from the parameters and permissions lists.
Defining an agent\'s capabilities in terms of solvable declarations effectively creates a vocabulary with which other agents can communicate with the new agent. Ensuring that agents will speak the same language and share a common, unambiguous semantics of the vocabulary involves ontology. Agent development tools and services (automatic translations of solvables by the facilitator) help address this issue; additionally, a preferred embodiment of the present invention will typically rely on vocabulary from either formally engineered ontologies for specific domains or from ontologies constructed during the incremental development of a body of agents for several applications or from both specific domain ontologies and incrementally developed ontologies. Several example tools and services are described in Cheyer et al.\'s paper entitled â€œDevelopment Tools for the Open Agent Architecture,â€ as presented at the Practical Application of Intelligent Agents and Multi-Agent Technology (PAAM 96), London, April 1996.
Although the present invention imposes no hard restrictions on the form of solvable declarations, two common usage conventions illustrate some of the utility associated with solvables.
Classes of services are often preferably tagged by a particular type. For instance, in the example above, the â€œlast_messageâ€ and â€œget_messageâ€ solvables are specialized for email, not by modifying the names of the services, but rather by the use of the â€˜emailâ€™ parameter, which serves during the execution of an ICL request to select (or not) a specific type of message.
Actions are generally written using an imperative verb as the functor of the solvable in a preferred embodiment of the present invention, the direct object (or item class) as the first argument of the predicate, required arguments following, and then an extensible parameter list as the last argument. The parameter list can hold optional information usable by the function. The ICL expression generated by a natural language parser often makes use of this parameter list to store prepositional phrases and adjectives.
As an illustration of the above two points, â€œSend mail to Bob about lunchâ€ will be translated into an ICL request send message(email, â€˜Bob Jonesâ€™, [subject(lunch)]), whereas â€œRemind Bob about lunchâ€ would leave the transport unspecified (send_message(KIND, â€˜Bob Jonesâ€™, [subject(lunch)])), enabling an available message transfer agents (e.g., fax, phone, mail, pager) to compete for the opportunity to carry out the request.
An agent preferably requests services of the community of agent by delegating tasks or goals to its facilitator. Each request preferably contains calls to one or more agent solvables, and optionally specifies parameters containing advice to help the facilitator determine how to execute the task. Calling a solvable preferably does not require that the agent specify (or even know of) a particular agent or agents to handle the call. While it is possible to specify one or more agents using an address parameter (and there are situations in which this is desirable), in general it is advantageous to leave this delegation to the facilitator. This greatly reduces the hard-coded component dependencies often found in other distributed frameworks. The agent libraries of a preferred embodiment of the present invention provide an agent with a single, unified point of entry for requesting services of other agents: the library procedure oaa_Solve. In the style of logic programming, oaa_Solve may preferably be used both to retrieve data and to initiate actions, so that calling a data solvable looks the same as calling a procedure solvable.
Complex Goal Expressions
A powerful feature provided by preferred embodiments of the present invention is the ability of a client agent (or a user) to submit compound goals of an arbitrarily complex nature to a facilitator. A compound goal is a single goal expression that specifies multiple sub-goals to be performed. In speaking of a â€œcomplex goal expressionâ€ we mean that a single goal expression that expresses multiple sub-goals can potentially include more than one type of logical connector (e.g., AND, OR, NOT), and/or more than one level of logical nesting (e.g., use of parentheses), or the substantive equivalent. By way of further clarification, we note that when speaking of an â€œarbitrarily complex goal expressionâ€ we mean that goals are expressed in a language or syntax that allows expression of such complex goals when appropriate or when desired, not that every goal is itself necessarily complex.
It is contemplated that this ability is provided through an interagent communication language having the necessary syntax and semantics. In one example, the goals may take the form of compound goal expressions composed using operators similar to those employed by PROLOG, that is, the comma for conjunction, the semicolon for disjunction, the arrow for conditional execution, etc. The present invention also contemplates significant extensions to PROLOG syntax and semantics. For example, one embodiment incorporates a â€œparallel disjunctionâ€ operator indicating that the disjuncts are to be executed by different agents concurrently. A further embodiment supports the specification of whether a given sub-goal is to be executed breadth-first or depth-first.
A further embodiment supports each sub-goal of a compound goal optionally having an address and/or a set of parameters attached to it. Thus, each sub-goal takes the form
where both Address and Parameters are optional.
An address, if present, preferably specifies one or more agents to handle the given goal, and may employ several different types of referring expression: unique names, symbolic names, and shorthand names. Every agent has preferably a unique name, assigned by its facilitator, which relies upon network addressing schemes to ensure its global uniqueness. Preferably, agents also have self-selected symbolic names (for example, â€œmailâ€ ), which are not guaranteed to be unique. When an address includes a symbolic name, the facilitator preferably takes this to mean that all agents having that name should be called upon. Shorthand names include â€˜selfâ€™ and â€˜parentâ€™ (which refers to the agent\'s facilitator). The address associated with a goal or sub-goal is preferably always optional. When an address is not present, it is the facilitator\'s job to supply an appropriate address.
The distributed execution of compound goals becomes particularly powerful when used in conjunction with natural language or speech-enabled interfaces, as the query itself may specify how functionality from distinct agents will be combined. As a simple example, the spoken utterance â€œFax it to Bill Smith\'s manager.â€ can be translated into the following compound ICL request:
- oaa_Solve((manager(â€˜Bill Smithâ€™, M), fax(it,M,[ ])), [strategy(action)])
Note that in this ICL request there are two sub-goals, â€œmanager(â€˜Bill Smithâ€™,M)â€ and â€œfax(it,M,[ ]),â€ and a single global parameter â€œstrategy(action).â€ According to the present invention, the facilitator is capable of mapping global parameters in order to apply the constraints or advice across the separate sub-goals in a meaningful way. In this instance, the global parameter strategy(action) implies a parallel constraint upon the first sub-goal; i.e., when there are multiple agents that can respond to the manager sub-goal, each agent should receive a request for service. In contrast, for the second sub-goal, parallelism should not be inferred from the global parameter strategy(action) because such an inference would possibly result in the transmission of duplicate facsimiles.
Refining Service Requests
In a preferred embodiment of the present invention, parameters associated with a goal (or sub-goal) can draw on useful features to refine the request\'s meaning. For example, it is frequently preferred to be able to specify whether or not solutions are to be returned synchronously; this is done using the reply parameter, which can take any of the values synchronous, asynchronous, or none. As another example, when the goal is a non-compound query of a data solvable, the cache parameter may preferably be used to request local caching of the facts associated with that solvable.
Many of the remaining parameters fall into two categories: feedback and advice. Feedback parameters allow a service requester to receive information from the facilitator about how a goal was handled. This feedback can include such things as the identities of the agents involved in satisfying the goal, and the amount of time expended in the satisfaction of the goal.
Advice parameters preferably give constraints or guidance to the facilitator in completing and interpreting the goal. For example, a solution_limit parameter preferably allows the requester to say how many solutions it is interested in; the facilitator and/or service providers are free to use this information in optimizing their efforts. Similarly, a time_limit is preferably used to say how long the requester is willing to wait for solutions to its request, and, in a multiple facilitator system, a level_limit may preferably be used to say how remote the facilitators may be that are consulted in the search for solutions. A priority parameter is preferably used to indicate that a request is more urgent than previous requests that have not yet been satisfied. Other preferred advice parameters include but are not limited to parameters used to tell the facilitator whether parallel satisfaction of the parts of a goal is appropriate, how to combine and filter results arriving from multiple solver agents, and whether the requester itself may be considered a candidate solver of the sub-goals of a request.
Advice parameters preferably provide an extensible set of low-level, orthogonal parameters capable of combining with the ICL goal language to fully express how information should flow among participants. In certain preferred embodiments of the present invention, multiple parameters can be grouped together and given a group name. The resulting high-level advice parameters can preferably be used to express concepts analogous to KQML\'s performatives, as well as define classifications of problem types. For instance, KQML\'s â€œask_allâ€ and â€œask_oneâ€ performatives would be represented as combinations of values given to the parameters reply, parallel ok, and solution_limit. As an example of a higher-level p