Abstract:
In one aspect this invention provides a data processing system ( 10 ) that includes a plurality of self-organizing software agents ( 40 ) capable of autonomously establishing relationships between themselves, where the totality of the relationships can be represented by a topological structure having nodes that each contain one of the plurality of software agents and links between the nodes that are the established relationships. The data processing system further includes a topology tuning function that obtains information that is descriptive of the topology and, based at least in part on the obtained information and on at least one criterion, that makes a recommendation to at least one of the plurality of software agents that is intended to modify the topology. In one embodiment the topology tuning function is performed by a topology tuner software agent ( 20 ), while in another embodiment the topology tuning function forms a part of a system hosting function, such as a part of the operating system of the system ( 10 ).

Description:
TECHNICAL FIELD  
       [0001]     This invention relates generally to data processing systems and networks that include a plurality of autonomous software agents capable of self-organizing behavior resulting in the formation of inter-agent relationships and, more specifically, this invention relates to methods and apparatus for optimizing or tuning a topology of inter-agent relationships.  
       BACKGROUND  
       [0002]     In multi-agent systems, agents form relationships among themselves according to their own internal preferences and decision-making logic. In general, there is no “dictator” function that determines the inter-relationships between agents. This level of self-organization is one of the defining features of multi-agent systems, and one of the most valuable.  
         [0003]     Nevertheless, it is often desirable that the topology of the web of inter-agent relationships exhibit certain globally-defined properties. This is especially true if the multi-agent system is under the nominal administration of a single entity, such as a corporation, or was configured to solve some cooperative problem. For example, so-called “random” networks, such as the network of physical internet routers, in which the degree-distribution of nodes roughly follows a bell-curve, are relatively robust against targeted attacks on nodes, because the ill effects of the failure of any one node is approximately the same for all nodes. On the other hand, “scale-free” networks, in which the degree-distribution of nodes follows a power law, are relatively robust against random node failure, because most nodes are relatively unimportant to the overall network&#39;s functioning. Reference in this regard can be made to Albert, R., Jeong, H., and Barabasi, A.-L., “Error and attack tolerance in complex networks”, Nature 406:378-381 (2000).  
         [0004]     For the purposes of this patent application, a “scale-free network” is any network of relationships in which the degree-distribution of the nodes is characterized by a power law. The “degree” of a node denotes the number of connections a given node has with other nodes, i.e., the number of relationships (or relationships of a given type) that a given node is in. Thus, for scale-free networks, the histogram of node-degrees has the feature that relatively fewer nodes are found to have relatively higher degrees, with the overall relationship following a power-law curve.  
         [0005]     It is also typically the case that the overall desired network topology can change with time. For example, during typical functioning it is desirable for the system to maintain robustness against random failure; but in the event of a real or an expected attack, it would be even more desirable for the system to instead protect itself against the attack. For this to occur the system should exhibit an ability to continually adjust the statistical properties of the network topology.  
         [0006]     A problem thus exists in the prior art as to how to dynamically and intelligently modify, or alter, or “tune” the topology of the network of relationships in an operating multi-agent system, in order to achieve a desired global behavior, such as robustness against attack or against random failure, without overly restricting the ability of agents to autonomously form and break relationships.  
         [0007]     There is a body of established work on the relationship between network topology and system robustness, especially the tradeoff between robustness against attack versus robustness against random failure, as was noted above. In addition, however, there exists relevant work on the relationship between the degree of inter-connectivity among nodes in a localized neighborhood, and the rate at which chain reactions of failures are propagated. Reference in this regard can be made to Keeling, M., “The effects of local spatial structure on epidemiological invasions”, Proc. Roy. Soc. Lond. B 266, 859-869 (1999). This previous work indicates that changes to the topological structure of the network of relationships can have a profound effect on system dynamics, and in particular can result in improved system performance in the face of different kinds of failure or attack.  
         [0008]     However, prior to this invention, there has been no description of a mechanism whereby these changes could be effected in the case of multi-agent systems.  
         [0009]     There has also been extensive work on so-called “self-healing networks”, in which elements of a network (e.g., internet or telecommunications routers) respond to failures of nodes by reconfiguring themselves in a distributed fashion. These approaches are sometimes proactive, in the sense that they attempt to prepare the system to optimally respond to failures in advance of the failure actually occurring. Reference in this regard can be made to U.S. Patent No. 6,061,735: “Network restoration plan regeneration responsive to network topology changes”, by James D. Rogers. However, this prior work does not address the need for systems to dynamically tune a preferred system topology to protect against different kinds of attack or failure, as the need arises.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0010]     The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings.  
         [0011]     In one aspect this invention provides a data processing system that includes a plurality of self-organizing software agents capable of autonomously establishing relationships between themselves, where the totality of the relationships can be represented by a topological structure having nodes that each comprise one of the plurality of software agents and links between the nodes that comprise the established relationships. The data processing system further includes a topology tuning function that obtains information that is descriptive of the topology and, based at least in part on the obtained information and on at least one criterion, that makes one or more recommendations to at least one of the plurality of software agents that is intended to modify the topology. In one embodiment the topology tuning function is performed by a topology tuner software agent, while in another embodiment the topology tuning function forms a part of a system hosting function, such as a part of the operating system or other system software (e.g., an application server such as one known as the WebSphere™ Application Server that is available from the assignee of this patent application.)  
         [0012]     In another aspect this invention provides, in a data processing system, a method to automatically tune a topology of relationships between a plurality of self-organizing agents. The method includes obtaining information that is descriptive of the topology and, based at least in part on the obtained information and on at least one criterion, making one or more recommendations to at least one of the plurality of agents that is intended to modify the topology of relationships between the plurality of self-organizing agents. This information may be obtained by the topology tuner agent by querying a system registry to determine identities of individual ones of the plurality of agents, and possibly also relationship information between the agents, and/or by querying individual ones of the plurality of agents to determine to which other agent or agents the individual one of the plurality of agents currently has a relationship.  
         [0013]     In a further aspect this invention provides a topology tuner software agent operable in a data processing system that includes the plurality of self-organizing software agents. The topology tuner software agent includes computer program code for obtaining information that is descriptive of a topology of relationships between the self-organizing software agents from a system registry function or from the self-organizing software agents themselves; and also computer program code that is responsive to the obtained information and at least one criterion, for making at least one recommendation to at least one of the plurality of self-organizing software agents that is intended to modify the topology. Obtaining information can be performed periodically by topology tuner software agent to update the state of the topology, and the topology tuner software agent can make the recommendation when some topology threshold condition is satisfied.  
         [0014]     In the various embodiments of this invention the at least one criterion may be a vulnerability of the topology to an attack directed to one or more of the self-organizing software agents, a vulnerability of the topology to a failure of one or more of the self-organizing software agents, and/or a rate at which the self-organizing software agents form new relationships.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein:  
         [0016]      FIG. 1  is a simplified block diagram showing an unevenly-distributed topology of agent relationships, and a topology tuner agent in accordance with this invention;  
         [0017]      FIG. 2  is a logic flow diagram showing a tuner agent life cycle;  
         [0018]      FIG. 3  is a logic flow diagram showing a process whereby the tuner agent gathers topology-related information;  
         [0019]      FIG. 4  is a logic flow diagram showing a process whereby the tuner agent tunes the unevenly-distributed topology of agent relationships; and  
         [0020]      FIG. 5  is a logic flow diagram showing a process whereby the tuner agent determines when to begin another topology tuning cycle. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]      FIG. 1  shows a multi-agent system  10  containing a topology tuner agent  20 , a registry service  30 , a directory service  50  and worker agents collectively referred to as agents  40 , and designated individually as A 01 -A 13 , B 1  and B 2 . All agents  40  are assumed to be registered with the registry service  30 . The relationships between the worker agents  40  are indicated by the lines connecting the agents which, for the purposes of this invention, is considered to represent a topology of agent inter-relationships. In this non-limiting example A 01 -A 12  are in a relationship with B 1 , which implies that the system  10  is extremely vulnerable to an attack directed against B  1 . As can be appreciated, the robustness of the system  10  to a targeted attack would be significantly increased if approximately half of the agents A 01 -A 13  were in a relationship with B 1 , and the other half were in a relationship with B 2 . In accordance with this invention, the tuner agent  20  operates to detect this imbalance in agent relationships, and further operates to re-balance, or tune, the resulting agent relationship topology so as to reduce the vulnerability of the system  10  to failure or malicious attack.  
         [0022]      FIG. 2  shows the major steps in the life cycle of the topology tuner agent  20 , while  FIGS. 3-5  shows the operation of these major steps in greater detail.  
         [0023]     Upon starting, at Block  210  the topology tuner agent  20  first obtains information about the current topology of relationships in the system  10 . This may take the form of an exhaustive list of all relationships between agents  40  in the system  10 , possibly labeled with identifiers to distinguish between different types of relationship. This information can be conveniently represented as a graph in which the agents  40  are nodes and relationships are arcs connecting nodes. Alternatively, the topology information may be represented by statistical measures of system topology, such as the distribution of the number relationships the agents  40  have. For example, the topology tuner agent  20  may construct a histogram of the number of relationships the agents  40  are in. In such a histogram, the ordinate or x-coordinate is the number of relationships, and the abscissa or y-coordinate gives the number of agents found to be in that number of relationships. To determine whether the system topology was more scale-free or random in character, the topology tuner agent  20  compares the shape of the histogram against two alternative representations, the Gaussian distribution and the power-law distribution, using conventional statistical curve-fitting techniques. The closer the histogram is to a Gaussian distribution, the more “random” is the topology, while histograms that resemble the power-law distribution indicate a scale-free topology. A preferred method of gathering this topology information is shown in  FIG. 3 , and is discussed below.  
         [0024]     Having gathered the topology information, at Block  220  the topology tuner agent  20  determines what type of tuning should be performed. This may be accomplished by starting with a high-level policy or goal, such as might be set by a system administrator, and calculating characteristics of the desired topology, and then comparing those characteristics with the characteristics of the measured topology. For example, the system administrator might specify that robustness under random node failure is a goal. The topology tuner agent  20  takes this predetermined goal and identifies a desired topology that most closely matches the topology required to achieve the goal, in this example a random graph. This implies that the topology tuner agent  20  attempts to achieve a normal or Gaussian distribution of connections per node (i.e., per each agent  40 ).  
         [0025]     It should be noted that the practice of this invention does not require a general purpose mapping between high-level goals and topological characteristics. It is sufficient for this invention to have the mapping be even so simple as a set of hand-coded rules that apply to different predefined goals.  
         [0026]     Once it has determined the type of tuning to be done, at Block  230  the topology tuner agent  20  contacts at least some of the agents  40  in the system  10  and directs them to modify their relationships in a particular way. This can be done in a multi-cast fashion, in which the topology tuner agent  20  sends the same message to all agents  40  at once; or it may be done in a more individualized, single-cast fashion, in which the agents  40  are contacted one by one, and each one potentially receives a different recommendation from the topology tuner agent  20 .  FIG. 4  shows a preferred method of carrying out this procedure.  
         [0027]     After completing a tuning process or cycle, the topology tuner agent  20  determines at Block  240  whether re-tuning is necessary. Re-tuning is necessary in general to deal with two kinds of change, both of which may occur at any time: (a) the desired topology may change in such a way that the current topology is no longer desirable, or (b) the actual topology may change in such a way that it no longer has the desired characteristics. The former may occur, for example, if the system administrator changes the primary goal from “stability under random failure” to “security against future targeted attack”. The latter may occur, for example, because the agents  40  in the system  10  change their relationships, or due to a failure of one or more agents  40 .  
         [0028]     If the topology tuner agent  20  determines that re-tuning is necessary, control passes back to Block  220 , otherwise the topology tuner agent  20  continues at Block  250  by monitoring the system topology and updating the topology information (possibly after a delay), and redetermining whether re-tuning is necessary. A preferred method of determining whether re-tuning is necessary and of updating the topology information is shown in  FIG. 5 .  
         [0029]      FIG. 3  illustrates a preferred method whereby the topology tuner agent  20  gathers information about the topology of the system  10 . First, the topology tuner agent  20  determines whether the topology information it needs is already available from another component in the system  10 . A preferred technique for storing this information is by means of a “relationship registry”. A relationship registry is an agent or service that keeps track of the relationships between the agents  40  in the system  10 . Relationship registries have many uses beyond that of the tuning of relationships in accordance with this invention: for example, they are useful for certain methods of performing fast detection and diagnosis of problems in the system  10 . For this reason, there is at least the possibility that the relationship information needed by the topology tuner agent  20  has already been gathered.  
         [0030]     Therefore, in the preferred embodiment the topology tuner agent  20  contacts at Block  310  the directory service  50  and requests information about relationship registries in the system  10 . If the directory service  50  returns the requested information at Block  320 , the topology tuner agent  20  selects one or more of the registries (such as the Registry Service  30  shown in  FIG. 1 ) and obtains at Block  330  the desired information about the topology of the relationships between the agents  40 . If, however, there is no relationship registry service  30  present in the system  10 , the topology tuner agent  20  instead directly gathers the topology information. This is preferably accomplished by obtaining at Block  340  a list of agents  40  to contact, and then at Block  350  contacting each agent  40  in the list and requesting from that agent the information that describes its relationships with other agents in the system  10 .  
         [0031]     After obtaining the topology information, either directly from the relationship register  30  or from the agents  40  themselves, the topology tuner agent  20  at Block  360  is enabled to calculate statistical measures of the system topology. For example, the topology tuner agent  20  may calculate the observed distribution in the number of relationships held by the agents  40 . In the case where there are multiple types of relationships present in the system  10 , the topology tuner agent  20  may calculate a distribution for each type of relationship.  
         [0032]     In summary,  FIG. 3  describes a presently preferred technique for gathering the topology information by the topology tuner agent  20 . In general, as opposed to querying the individual agents  40  about their relationships, the topology tuner agent  20  may make use of the central registry  30  and/or the directory  50  in which information about the relationships of the agents  40  is stored. It is preferred that the registry  30  be kept up to date in some manner, such as by periodically receiving updates from the agents  40 , or by periodically polling the agents  40 .  
         [0033]     There are various techniques for monitoring the topology of agent  40  relationships in the system  10 . For example, the agents  40  may inform the topology tuner agent  20  whenever their relationships change; or the agents  40  may inform the relationship registry  30 , which in turn informs the topology tuner agent  20 , or the topology tuner agent  20  may poll the agents  40 , or the relationship registry  30 . Combinations of these techniques can be used as well.  
         [0034]      FIG. 4  shows a presently preferred method whereby the topology tuner agent  20  performs the tuning the system  10  topology in a single operation. At Block  410  the topology tuner agent  20  obtains a general recommendation describing what type of tuning is to be preformed. An example of a general recommendation, which would be used to create a random graph, would be, “Re-form all relationships”.  
         [0035]     At Block  420  the topology tuner agent  20  obtains, such as from the directory service  50 , a list of agents  40  to make the recommendation to. This could be the entire population of agents  40 , or a subset of the population for which a sub-graph topology is to be tuned. Alternatively, the list of agents  40  may comprise a subset of the population selected by relationship type, if the recommendation only applies to certain types of relationship.  
         [0036]     Next the topology tuner agent  20  enters a loop to contact the agents on the list. If at Block  430  it finds that the list is empty, the topology tuner agent  20  exits the loop and this instance of the tuning process is complete (Block  470 ). Otherwise, the topology tuner agent  20  selects (and removes) an agent  40  from the list (Block  440 ). At Block  450  the topology tuner agent  20  may tailor its recommendation to the selected agent. For example, it may be the case that the selected agent must receive the recommendation in a different form than that of the general recommendation, it being assumed that this type of information may have been obtained along with the agent&#39;s directory entry. Another example concerns the case where the recommendation involves only certain types of relationship, and the selected agent is known not to be capable of forming relationships of that type. In this case the topology tuner agent  20  need not send the recommendation at all. At Block  460  the topology tuner agent  20  sends the customized recommendation and proceeds to select another agent  40  from the list.  
         [0037]     It should be noted that the topology tuner agent  20  may measure or estimate the topology and/or distance from the desired topology characteristics at interim points while tuning, and thus may terminate the method early. In this case there would be another decision block in the loop, and an alternative exit to Block  470 .  
         [0038]     In general, there are various forms that the recommendations made by the topology tuner agent  20  can take. For example, the recommendations can include: (a) “re-form your relationships”, optionally with a relationship category; (b) “select an agent from a provided list”, optionally with a relationship category; and (c)“select an agent not on a provided list”, optionally with a relationship category. In this latter case, it can be appreciated that if the list includes one or more agents that the agent  40  currently has a relationship with, then the execution of this latter recommendation can have the effect of causing the agent  40  to break its relationship with one or more other agents  40  that are found on the list, and to form new relationships with other agents.  
         [0039]     Depending on the particular situation, the topology tuner agent  20  can tune the network of agent  40  relationships for a number of different purposes. Some non-limiting examples are now presented.  
         [0040]     The topology tuner agent  20  can tune the network of agent  40  relationships to enhance security against a future targeted attack (i.e., an attack that includes the choice of a target). It does this by requesting all or some of the agents  40  to re-form their relationships, without constraining the set of potential partners. The result is a shift toward a random-graph topology.  
         [0041]     The topology tuner agent  20  can tune the network of agent  40  relationships to enhance robustness against random failure. It does this by requesting all or some of the agents  40  to re-form their relationships, giving preferential treatment to agents  40  in a selected list. The list is generated, and modified as the topology tuner agent  20  performs its assigned task, such that the resulting topology is or approaches that of a scale-free network.  
         [0042]     The topology tuner agent  20  can tune the network of agent  40  relationships to provide protection against an attack on known or suspected target agent(s). It does this by requesting all or some of the agents  40  to re-form their relationships, and selecting partner agents that are not on a list of at-risk agents. The result is a network in which at-risk agents have few relationships, while the remainder of the agents  40  tend toward a random-graph topology.  
         [0043]     The topology tuner agent  20  can tune the network of agent  40  relationships to provide protection against a possible failure of known agents. In a manner similar to the foregoing case, it does this by requesting all or some of the agents  40  to re-form their relationships, and selects partner agents that are not on a list of agents that are at-risk for failure. The result is a network in which at-risk for failure agents have few relationships, while the remainder of the agents  40  tend toward the random-graph topology.  
         [0044]     The topology tuner agent  20  can tune the network of agent  40  relationships to provide for a reduction of “churn” or oscillations in system  10  topology, by reducing the rate of relationship change. This can be accomplished by selecting a subset of agents  40  (or all of the agents  40 ), and requesting those agents  40  in the selected subset to not re-form their relationships with other agents  40  for some specified period of time.  
         [0045]     The topology tuner agent  20  can tune the network of agent  40  relationships to provide increasing system dynamism and responsiveness by increasing the rate of relationship change. This can be accomplished by selecting a subset of agents  40  (or all of the agents  40 ), and requesting those agents  40  in the selected subset to re-form their relationships with other agents  40 . Depending on the frequency of the request, the agents  40  in the selected sub-set will tend to re-form their relationships with other agents at a rate that exceeds the rate of relationship reformation of the general population of the agents  40 .  
         [0046]     As was shown in  FIG. 2 , once the topology tuner agent  20  has completed a single step (or cycle) of tuning, it determines whether and when to start another cycle (Block  240 ).  FIG. 5  shows a preferred method of making the re-tuning determination, which includes the consideration that the topology of the system  10  may change (or “drift”) on its own, independent of any action performed by the topology tuner agent  20 .  FIG. 5  thus subsumes the Blocks  240  and  250  of  FIG. 2 .  
         [0047]     From the start state (Block  500 ), the topology tuner agent  20  first determines at Block  510  whether the topology information it has previously gathered is still sufficiently close to the desired topology. One simple technique to make this determination involves comparing a measured statistic, such as the distribution of number of relationships, with a goal statistic. The goal statistic may have been obtained in Block  220  of  FIG. 2  when the topology tuner agent  20  determined what type of tuning was to be done. It should be noted that the goal may have changed since the last tuning cycle.  
         [0048]     If the measured topology does differ from the goal, then control transfers to Block  570  where the topology tuner agent  20  begins a new tuning cycle, also shown as the transition from Block  240  to Block  220  in  FIG. 2 .  
         [0049]     If the measured topology is still sufficiently close to the desired topology, the topology tuner agent  20  estimates whether the actual system  10  may have drifted sufficiently far from the desired topology in the time since the last measurement (Block  520 ). The actual method whereby the topology tuner agent  20  estimates the drift in the system  10  topology can be any suitable method, and can incorporate any standard technique for time-series estimation, such as linear forecasting.  
         [0050]     If the estimated drift exceeds an acceptable threshold limit, the topology tuner agent  20  begins another tuning cycle by transferring to Block  540 , otherwise the topology tuner agent  20  waits at Block  530  for some period of time. Note that, like the desired topology, the acceptable threshold limit may have changed since the last comparison. For example, the system administrator may adjust the threshold to reflect changing high-level goals, or the topology tuner agent may calculate the threshold dynamically. Thus, the threshold that determines when to begin a new topology tuning cycle may be a variable threshold. The period of time may follow a predetermined schedule, or it may be dependent on the estimated drift rate, or it may be dependent on some other parameter or parameters (such as a historical drift rate under some certain set of system  10  conditions). The waiting period at Block  530  may be interrupted if the topology tuner agent  20  receives a new topology goal, or if it receives an express notification that the topology has changed.  
         [0051]     At Block  540  the topology tuner agent  20  updates its measured topology information, which corresponds to Block  250  of  FIG. 2 . The topology tuner agent  20  preferably updates the measured topology information using the same method that it used to gather topology information in the first instance, for example, according to the method of  FIG. 3 . However, updating the topology information may differ from the initial information gathering process. For example, the topology tuner agent  20  may keep track of how frequently different ones of the agents  40  change their relationships (e.g., it may monitor an agent “fickleness” parameter), and may choose to re-measure the more fickle agents more frequently.  
         [0052]     Following re-measurement of the system  10  topology, at Block  550  the topology tuner agent  20  updates its model of the system drift, e.g., by adjusting the estimated linear drift rate, and then returns to Block  510 .  
         [0053]     It should thus be appreciated that the decision as to when to begin another tuning cycle ( FIG. 2 , Block  240 , and  FIG. 5 ) can be accomplished by continually updating the topology information, re-calculating statistics, and then initiating another tuning cycle when a statistic or statistics reaches a threshold, or it could be accomplished continuously.  
         [0054]     Based on the foregoing description of the presently preferred embodiments of this invention, it should be appreciated that an aspect of this invention is to execute, in the multi-agent system  10 , the functionality inherent in the topology tuner agent  20 . The topology tuner agent  20  gathers statistical information about the relationship-network&#39;s topology (such as the degree-distribution of nodes), and then makes recommendations to individual ones of the agents  40  to modify their relationships (if needed).  
         [0055]     The topology tuner agent  20  is preferably endowed with special privileges, giving it sufficient nominal authority to make its recommendations to the other agents  40  effective, but otherwise preferably behaves as a “peer” agent. For example, the topology tuner agent  20  preferably uses the same messaging infrastructure as all other agents  40 .  
         [0056]     An aspect of this invention is the operation of the topology tuner agent  20  in gathering information about the network topology of the system  10 , as was described above in relation to Block  210  of  FIG. 2  and the method illustrated more specifically in  FIG. 3 . To summarize, the topology tuner agent  20  first fetches, preferably from the public directory service(s)  50  and/or  30 , the list of agents  40  in the system  10 , or a sub-set of them. If the relationship information is not inherently provided with the list of agents, then for each agent  40  in the list the topology tuner agent  20  may send a query about that agent&#39;s current relationships. As one example, the query may take the form: “tell me who you purchase supplies from”. The query would preferably request information regarding only long-term or recurring relationships. By asking the agents  40  for their relationships in turn the topology tuner agent  20  gradually assembles a graph of the relationships amongst the agents  40 . The graph, which may resemble the one shown in  FIG. 1 , need not be perfectly accurate, as at least some relationships may typically change while the graph is being assembled, however it is sufficient for use in making approximate statistical inferences, such as determining the degree-distribution and other agent  40  relatedness information.  
         [0057]     As was noted above, it is also within the scope of this invention to classify relationships between agents  40  according to some classification scheme (e.g., “relationships concerning storage services” versus “relationships concerning bandwidth services”), thereby identifying different kinds of links between topological network nodes (i.e., between agents  40 ). To perform this function the topology tuner agent  20  need not be endowed with any “understanding” of the meaning of the various relationship categories, but only with the ability to identify to which category a given link belongs. As such, the category determination may be based simply on keyword matching.  
         [0058]     Once the network topology graph is constructed, the topology tuner agent  20  identifies those agents  40  (i.e., network nodes) with an undesirable property or properties. For example, to make the network more robust against attack, the topology tuner agent  20  locates the nodes with the greatest number of links (of one or more categories) with other nodes. It then finds those “neighbor” agents (i.e., the agents linked to the agent that has been identified), and recommends to one or more of those agents that they link to a different node (i.e., that they link to a different one of the agents  40 ).  
         [0059]     This recommendation may take several forms, from expressly identifying a particular one of the agents  40  to link to, to identifying a set of preferred agents  40  to link to, or to simply requesting that the agent break the existing link and select any other agent to link to according to its own preferences.  
         [0060]     In a preferred embodiment of this invention the topology tuner agent  20  also requests that each neighbor agent return, to the topology tuner agent  20 , a ranked list of alternate agents that the neighbor agent would find acceptable. Using this returned list, the topology tuner agent  20  is enabled to select one or more other agents that a particular agent  40  would find preferable. However, the topology tuner agent  20  is not obligated to offer a particular agent  40  one of its preferred agents to form a relationship with, as the topology tuner agent  20  may have knowledge that the preferred agent  40  is actually one that is a probable target for an attack, or a probable candidate for a failure.  
         [0061]     An aspect of this invention involves a consideration of, and a compensation for, system  10  dynamics. During the time that the topology tuner agent  20  is gathering information and making recommendations, the agents  40  in the system  10  are carrying out their assigned tasks. This implies that the network of relationships is most likely continually changing, independent of the activities of the topology tuner agent  20 . It is thus preferred that the topology tuner agent  20  incorporate the dynamics of the system  10  into its internal model.  
         [0062]     This can be accomplished in several ways. For example, and as was discussed above in reference to  FIGS. 2 and 5 , the topology tuner agent  20  may revisit the agents  40  from time to time in order to update the acquired information about the network of relationships. The topology tuner agent  20  can use the updated information to measure the extent to which the statistical properties of the network topology have changed since the last update, and therefore arrive at an estimated overall rate of change in the statistics. This rate of change can then be used to determine a minimum or an optimal frequency at which the topology tuner agent  20  should revisit the agents  40  in the system  10  to determine their current relationships, and consequently the frequency at which it must issue or reissue recommendations to the agents  40  in the system  10 .  
         [0063]     The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best method and apparatus presently contemplated by the inventors for carrying out the invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims.  
         [0064]     As but some examples of modifications and adaptions that may occur to those skilled in the art, it should be noted that the topology tuning function need not be implemented as the software agent  20 , but could, instead, be implemented as a part of the hosting environment, such as by an entity that resides in the hosting environment.  
         [0065]     Also, the foregoing description of the topology tuner agent  20  has assumed that there is no centralized control of the system  10 , and possibly no centrally stored information that is descriptive of the topological properties of the agent  40  relationships. However, the topology tuner agent  20  may also be of use in situations where there is some degree of centralized control and/or centrally stored information.  
         [0066]     For example, it may be the case that all of the agents  40  in a multi-agent system  10  have been programmed to follow a common set of policies. Typically in such situations, these policies specify a core set of common behaviors to which the agents  40  must conform, but do not fully specify the behavior of each individual one of the agents  40 . In this case the agents  40  can obtain updates to the common set of policies from time to time, and change their behavior accordingly. In such a situation the recommendations of the topology tuner agent  20  may be incorporated into the common set of core policies and transmitted to the other agents  40  by means of a policy update, rather than by direct interaction between the topology tuner agent  20  and the agents  40  of the system  10 .  
         [0067]     The use of other similar or equivalent techniques and procedures may thus be attempted by those skilled in the art. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention.  
         [0068]     Furthermore, some of the features of the present invention could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the present invention, and not in limitation thereof.