1 Scope
This document is part of the FIPA specifications covering agent management for inter-operable agents. This specification incorporates and further enhances [FIPA00002] and [FIPA00067] represents a companion specification.
This document contains specifications for agent management including agent management services, agent management ontology and agent platform message transport. This document is primarily concerned with defining open standard interfaces for accessing agent management services. The internal design and implementation of intelligent agents and agent management infrastructure is not mandated by FIPA and is outside the scope of this specification.
The document provides a series of examples to illustrate the agent management functions defined.
2 Agent Management Reference Model
Agent management provides the normative framework within which FIPA agents exist and operate. It establishes the logical reference model for the creation, registration, location, communication, migration and retirement of agents.
The entities contained in the reference model (see Figure 1) are logical capability sets (that is, services) and do not imply any physical configuration. Additionally, the implementation details of individual APs and agents are the design choices of the individual agent system developers.
Figure 1: Agent Management Reference Model
The agent management reference model consists of the following logical components[1], each representing a capability set (these can be combined in physical implementations of APs):
· An agent is a computational process that implements the autonomous, communicating functionality of an application. Agents communicate using an Agent Communication Language. An Agent is the fundamental actor on an AP which combines one or more service capabilities, as published in a service description, into a unified and integrated execution model. An agent must have at least one owner, for example, based on organisational affiliation or human user ownership, and an agent must support at least one notion of identity. This notion of identity is the Agent Identifier (AID) that labels an agent so that it may be distinguished unambiguously within the Agent Universe. An agent may be registered at a number of transport addresses at which it can be contacted.
· A Directory Facilitator (DF) is an optional component of the AP, but if it is present, it must be implemented as a DF service (see Section 4.1). The DF provides yellow pages services to other agents. Agents may register their services with the DF or query the DF to find out what services are offered by other agents. Multiple DFs may exist within an AP and may be federated. The DF is a reification of the Agent Directory Service in [FIPA00001].
· An Agent Management System (AMS) is a mandatory component of the AP. The AMS exerts supervisory control over access to and use of the AP. Only one AMS will exist in a single AP. The AMS maintains a directory of AIDs which contain transport addresses (amongst other things) for agents registered with the AP. The AMS offers white pages services to other agents. Each agent must register with an AMS in order to get a valid AID. The AMS is a reification of the Agent Directory Service in [FIPA00001].
· An Message Transport Service (MTS) is the default communication method between agents on different APs (see [FIPA00067]).
· An Agent Platform (AP) provides the physical infrastructure in which agents can be deployed. The AP consists of the machine(s), operating system, agent support software, FIPA agent management components (DF, AMS and MTS) and agents.
The internal design of an AP is an issue for agent system developers and is not a subject of standardisation within FIPA. AP’s and the agents which are native to those APs, either by creation directly within or migration to the AP, may use any proprietary method of inter-communication.
It should be noted that the concept of an AP does not mean that all agents resident on an AP have to be co-located on the same host computer. FIPA envisages a variety of different APs from single processes containing lightweight agent threads, to fully distributed APs built around proprietary or open middleware standards.
FIPA is concerned only with how communication is carried out between agents who are native to the AP and agents outside the AP. Agents are free to exchange messages directly by any means that they can support.
· Software describes all non-agent, executable collections of instructions accessible through an agent. Agents may access software, for example, to add new services, acquire new communications protocols, acquire new security protocols/algorithms, acquire new negotiation protocols, access tools which support migration, etc.
3 Agent Naming
The FIPA agent naming reference model identifies an agent through an extensible collection of parameter-value pairs[2], called an Agent Identifier (AID). The extensible nature of an AID allows it to be augmented to accommodate other requirements, such as social names, nick names, roles, etc. which can then be attached to services within the AP. An AID comprises[3] (see Section 6.1.1):
· The name parameter, which is a globally unique identifier that can be used as a unique referring expression of the agent. One of the simplest mechanisms is to construct it from the actual name of the agent and its home agent platform address[4] (HAP), separated by the @ character. This is a reification of the notion of an Agent Name from [FIPA00001].
· The addresses parameter, which is a list of transport addresses where a message can be delivered (see Section 3.1). This is a reification of the notion of a Locator from [FIPA00001].
· The resolvers parameter, which is a list of name resolution service addresses (see Section 3.2).
The parameter values of an AID can be edited or modified by an agent, for example, to update the sequence of name resolution servers or transport addresses in an AID. However, the mandatory parameters can only be changed by the agent to whom the AID belongs. AIDs are primarily intended to be used to identify agents inside the envelope of a transport message, specifically within the to and from parameters (see [FIPA00067]).
Two AIDs are considered to be equivalent if their name parameters are the same.
3.1 Transport Addresses
A transport address is a physical address at which an agent can be contacted and is usually specific to a Message Transport Protocol. A given agent may support many methods of communication and can put multiple transport address values in the addresses parameter of an AID.
The EBNF syntax of a transport addresses is the same as for a URL given in [RFC2396]. [FIPA00067] describes the semantics of message delivery with regard to transport addresses.
3.2 Name Resolution
Name resolution is a service that is provided by the AMS through the search function. The resolvers parameter of the AID contains a sequence of AIDs at which the AID of the agent can ultimately be resolved into a transport address or set of transport address.
An example name resolution pattern might be:
1. agent-a wishes to send a message to agent-b, whose AID is:
(agent-identifier
:name agent-b@bar.com
:resolvers (sequence
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))))
and agent-a wishes to know additional transport addresses that have been given for agent-b.
2. Therefore, agent-a can send a search request to the first agent specified in the resolvers parameter which is typically an AMS. In this example, the AMS at foo.com.
3. If the AMS at foo.com has agent-b registered with it, then it returns a result message containing the AMS agent description of agent-b; if not, then a failed message is returned.
4. Upon receipt of the result message, agent-a can extract the agent-identifier parameter of the ams-agent-description and then extract the addresses parameter of this to determine the transport address(es) of agent-b.
5. agent-a can now send a message to agent-b by inserting the addresses parameter into the AID of agent-b.
4 Agent Management Services
4.1 Directory Facilitator
4.1.1 Overview
A DF is a component of an AP that provides a yellow pages directory service to agents; . It is the trusted, benign custodian of the agent directory. It is trusted in the sense that it must strive to maintain an accurate, complete and timely list of agents. It is benign in the sense that it must provide the most current information about agents in its directory on a non-discriminatory basis to all authorised agents. At least one DF must be resident on each AP (the default DF). However, an AP may support any number of DFs and DFs may register with each other to form federations.
Every agent that wishes to publicise its services to other agents, should find an appropriate DF and request the registration of its agent description. There is no intended future commitment or obligation on the part of the registering agent implied in the act of registering. For example, an agent can refuse a request for a service which is advertised through a DF. Additionally, the DF cannot guarantee the validity or accuracy of the information that has been registered with it, neither can it control the life cycle of any agent. An object description must be supplied containing values for all of the mandatory parameters of the description. It may also supply optional and private parameters, containing non-FIPA standardised information that an agent developer might want included in the directory. The deregistration function has the consequence that there is no longer a commitment on behalf of the DF to broker information relating to that agent. At any time, and for any reason, the agent may request the DF to modify its agent description.
An agent may search in order to request information from a DF. The DF does not guarantee the validity of the information provided in response to a search request, since the DF does not place any restrictions on the information that can be registered with it. However, the DF may restrict access to information in its directory and will verify all access permissions for agents which attempt to inform it of agent state changes.
The default DF on an AP has a reserved AID of:
(agent-identifier
:name df@hap_name[5]
:addresses (sequence hap_transport_address))
4.1.2 Management Functions Supported by the Directory Facilitator
In order to access the directory of agent descriptions managed by the DF, each DF must be able to perform the following functions, when defined on the domain of objects of type df-agent-description in compliance with the semantics described in Section 6.1.2:
· register
· deregister
· modify
· search
4.1.3 Federated Directory Facilitators
The DF encompasses a search mechanism that searches first locally and then extends the search to other DFs, if allowed. The default search mechanism is assumed to be a depth-first search across DFs. For specific purposes, optional constraints can be used as described in Section 6.1.4 such as the number of answers (max-results). The federation of DFs for extending searches can be achieved by DFs registering with each other with fipa-df as the value of the type parameter in the service-description.
When a DF receives a search action, it may determine whether it needs to propagate this search to other DFs that are registered with it[6]. It should only forward searches where the value of the max-depth parameter is greater than 1 and where it has not received a prior search with the same search-id parameter. If it does forward the search action, then it must use the following rules:
1. It must not change the value of the search-id parameter when it propagates the search and the value of all search-id parameters should be globally unique.
2. Before propagation, it should decrement the value of the max-depth parameter by 1.
4.2 Agent Management System
4.2.1 Overview
An AMS is a mandatory component of the AP and only one AMS will exist in a single AP. The AMS is responsible for managing the operation of an AP, such as the creation of agents, the deletion of agents and overseeing the migration of agents to and from the AP (if agent mobility is supported by the AP). Since different APs have different capabilities, the AMS can be queried to obtain a description of its AP. A life cycle is associated with each agent on the AP (see Section 5.1) which is maintained by the AMS.
The AMS represents the managing authority of an AP and if the AP spans multiple machines, then the AMS represents the authority across all machines. An AMS can request that an agent performs a specific management function, such as quit (that is, terminate all execution on its AP) and has the authority to forcibly enforce the function if such a request is ignored.
The AMS maintains an index of all the agents that are currently resident on an AP, which includes the AID of agents. Residency of an agent on the AP implies that the agent has been registered with the AMS. Each agent, in order to comply with the FIPA reference model, must register with the AMS of its HAP.
Agent descriptions can be later modified at any time and for any reason. Modification is restricted by authorisation of the AMS. The life of an agent with an AP terminates with its deregistration from the AMS. After deregistration, the AID of that agent can be removed by the directory and can be made available to other agents who should request it.
Agent description can be searched with the AMS and access to the directory of ams-agent-descriptions is further controlled by the AMS; no default policy is specified by this specification. The AMS is also the custodian of the AP description that can be retrieved by requesting the action get-description.
The AMS on an AP has a reserved AID of:
(agent-identifier
:name ams@hap_name[7]
:addresses (sequence hap_transport_address))
The name parameter of the AMS (ams@hap_name) is considered to be the Service Root of the AP (see [FIPA00001]).
4.2.2 Management Functions Supported by the Agent Management System
An AMS must be able to perform the following functions, in compliance with the semantics described in Section 6.1.5 (the first four functions are defined within the scope of the AMS, only on the domain of objects of type ams-agent-description and the last on the domain of objects of type ap-description):
· register
· deregister
· modify
· search
· get-description
In addition to the management functions exchanged between the AMS and agents on the AP, the AMS can instruct the underlying AP to perform the following operations:
· Suspend agent,
· Terminate agent,
· Create agent,
· Resume agent execution,
· Invoke agent,
· Execute agent, and,
· Resource management.
4.3 Message Transport Service
The Message Transport Service (MTS) delivers messages between agents within an AP and to agents that are resident on other APs. All FIPA agents have access to at least one MTS and only messages addressed to an agent can be sent to the MTS. See [FIPA00067] for more information on the MTS.
5 Agent Platform
5.1 Agent Life Cycle
FIPA agents exist physically on an AP and utilise the facilities offered by the AP for realising their functionalities. In this context, an agent, as a physical software process, has a physical life cycle that has to be managed by the AP. This section describes a possible life cycle that can be used to describe the states which it is believed are necessary and the responsibilities of the AMS in these states.
The life cycle of a FIPA agent is (see Figure 2):
· AP Bounded
An agent is physically managed within an AP and the life cycle of a static agent is therefore always bounded to a specific AP.
· Application Independent
The life cycle model is independent from any application system and it defines only the states and the transitions of the agent service in its life cycle.
· Instance-Oriented
The agent described in the life cycle model is assumed to be an instance (that is, an agent which has unique name and is executed independently).
· Unique
Each agent has only one AP life cycle state at any time and within only one AP.
Figure 2: Agent Life Cycle
The followings are the responsibility that an AMS, on behalf of the AP, has with regard to message delivery in each state of the life cycle of an agent:
· Active
The MTS delivers messages to the agent as normal.
· Initiated/Waiting/Suspended
The MTS either buffers messages until the agent returns to the active state or forwards messages to a new location (if a forward is set for the agent).
· Transit
The MTS either buffers messages until the agent becomes active (that is, the move function failed on the original AP or the agent was successfully started on the destination AP) or forwards messages to a new location (if a forward is set for the agent). Notice that only mobile agents can enter the Transit state. This ensures that a stationary agent executes all of its instructions on the node where it was invoked.
· Unknown
The MTS either buffers messages or rejects them, depending upon the policy of the MTS and the transport requirements of the message.
The state transitions of agents can be described as:
· Create
The creation or installation of a new agent.
· Invoke
The invocation of a new agent.
· Destroy
The forceful termination of an agent. This can only be initiated by the AMS and cannot be ignored by the agent.
· Quit
The graceful termination of an agent. This can be ignored by the agent.
· Suspend
Puts an agent in a suspended state. This can be initiated by the agent or the AMS.
· Resume
Brings the agent from a suspended state. This can only be initiated by the AMS.
· Wait
Puts an agent in a waiting state. This can only be initiated by an agent.
· Wake Up
Brings the agent from a waiting state. This can only be initiated by the AMS.
The following two transitions are only used by mobile agents:
· Move
Puts the agent in a transitory state. This can only be initiated by the agent.
· Execute
Brings the agent from a transitory state. This can only be initiated by the AMS.
5.2 Agent Registration
There are three ways in which an agent can be registered with an AMS:
· The agent was created on the AP.
· The agent migrated to the AP, for those APs which support agent mobility.
· The agent explicitly registered with the AP.
Agent registration involves registering an AID with the AMS. When an agent is either created or registers with an AP, the agent is registered with the AMS, for example by using the register function. In the following example, an agent called discovery-agent is registering with an AP located at foo.com. The agent discovery-agent was created on the AP (that is, discovery-agent’s HAP) at bar.com and requests that the AMS registers it.
For example:
:sender
(agent-identifier
:name discovery-agent@bar.com
:addresses (sequence iiop://bar.com/acc))
:receiver (set
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc)))
:ontology fipa-agent-management
:language fipa-sl0
:protocol fipa-request
:content
"((action
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(:ams-description
:name
(agent-identifier
:name discovery-agent@bar.com
:addresses (sequence iiop://bar.com/acc))
...)))")
It should be noted that the addresses parameter of the AID represents the transport address(es) that the agent would like any messages directed to (see [FIPA00067] for information on how the MTS deals with this). In the above example, the agent discovery-agent registers itself with the foo.com AP but by virtue of specifying a different transport address in the addresses parameter of its AID, messages that arrive at foo.com will be forwarded to bar.com.
5.2.1 Registration Lease Times
To enable the DF to manage a maintainable number of registrations over a long period of time, the DF may implement lease times using the lease-time parameter of a df-agent-description. A lease time is either a duration of time, such as 3 hours, or an absolute time, such as 08:00 26-Jul-2002, at which point a registration made by an agent can be removed from the DF registration database.
When an agent wishes to register with a DF, it can specify a lease time which is how long it would like the registration to be kept. If this lease time is okay for the DF, then it will accept the registration as usual and the value of the lease-time parameter in the content of the inform reply will be the same. Consequently, when the lease time expires, the registration will be silently removed by the DF. On the other hand, if the lease time is not acceptable to the DF, then the DF can include a new lease time as the value of the lease-time parameter in the content of the inform reply. This is the case when an agent does not specify a lease time in its registration.
If the DF does not support lease times, it will notify to the requesting agent that its registration is valid for an unlimited time by removing this parameter in the content of the inform reply, in fact the default lease-time is defined to be unlimited.
For example, and agent may register the following df-agent-description:
(request
...
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:protocols fipa-request
:ontologies (set fipa-agent-management)
:languages (set fipa-sl0)
:lease-time +00000000T600000000T
...")
Then if the DF agrees to this lease time, it will reply with and inform which contains the same value for the lease-time parameter:
(inform
...
:content
"((done
(action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:protocols (set fipa-request application-protocol)
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:lease-time +00000000T600000000T
...")
If an agent wishes to renew a lease time, then it can use the modify action to specify a new value for the lease-time parameter. The verification of this lease time goes through the same procedure mentioned in the last paragraph: if it is okay, then the value of the lease-time parameter in the content of the inform reply will be the same, if it is not okay, the value of the lease-time parameter in the content of the inform reply will be a new value which is acceptable to the DF.
6 Agent Management Ontology
6.1 Object Descriptions
This section describes a set of frames that represent the classes of objects in the domain of discourse within the framework of the fipa-agent-management ontology. The closure of symbols of this ontology can be obtained from [FIPA00067] that specifies additional set of frames of this ontology.
This ontology does not specify any specific positional order to encode the parameters of the objects. Therefore, it is required to encode objects in SL by specifying both the parameter name and the parameter value (see Section 3.6 of [FIPA00008]).
The following terms are used to describe the objects of the domain:
· Frame. This is the mandatory name of this entity that must be used to represent each instance of this class.
· Ontology. This is the name of the ontology, whose domain of discourse includes the parameters described in the table.
· Parameter. This is the mandatory name of a parameter of this frame.
· Description. This is a natural language description of the semantics of each parameter.
· Presence. This indicates whether each parameter is mandatory or optional.
· Type. This is the type of the values of the parameter: Integer, Word, String, URL, Term, Set or Sequence.
· Reserved Values. This is a list of FIPA-defined constants that can assume values for this parameter.
6.1.1 Agent Identifier Description
This type of object represents the identification of the agent. The addresses parameter and the name resolution mechanism (see Section 3.2), is a reification of the notion of Locator from [FIPA00001]. See also Section 3.3.7 in FIPA Agent Message Transport Service [FIPA00067] specifications.
|
Frame Ontology |
agent-identifier fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
name |
The symbolic name of the agent. |
Mandatory |
word |
df@hap_name ams@hap_name |
|
addresses |
A sequence of ordered transport addresses where the agent can be contacted. The order implies a preference relation of the agent to receive messages over that address. |
Optional |
Sequence of url |
|
|
resolvers |
A sequence of ordered AIDs where name resolution services for the agent can be contacted. The order in the sequence implies a preference in the list of resolvers. |
Optional |
Sequence of agent-identifier |
|
6.1.2 Directory Facilitator Agent Description
This type of object represents the description that can be registered with the DF service. This is a reification of the Agent Directory Entry from [FIPA00001].
|
Frame Ontology |
df-agent-description fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
name |
The identifier of the agent. |
Optional |
agent-identifier[8] |
|
|
services |
A list of services supported by this agent. |
Optional |
Set of service-description |
|
|
protocols |
A list of interaction protocols supported by the agent. |
Optional |
Set of string |
See [FIPA00025] |
|
ontologies |
A list of ontologies known by the agent. |
Optional |
Set of string |
fipa-agent-management |
|
languages |
A list of content languages known by the agent. |
Optional |
Set of string |
fipa-sl fipa-sl0 fipa-sl1 fipa-sl2 |
|
lease-time |
The duration or time at which the lease for this registration will expire[9]. |
Optional |
datetime[10] |
|
6.1.3 Service Description
This type of object represents the description of each service registered with the DF.
|
Frame Ontology |
service-description fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
name |
The name of the service. |
Optional |
string |
|
|
type |
The type of the service. |
Optional |
string |
fipa-df[11] fipa-ams |
|
protocols |
A list of interaction protocols supported by the service. |
Optional |
Set of string |
|
|
ontologies |
A list of ontologies supported by the service. |
Optional |
Set of string |
fipa-agent-management |
|
languages |
A list of content languages supported by the service. |
Optional |
Set of string |
|
|
ownership |
The owner of the service |
Optional |
string |
|
|
properties |
A list of properties that discriminate the service. |
Optional |
Set of property |
|
6.1.4 Search Constraints
This type of object represents a set of constraints to limit the function of searching within a directory.
|
Frame Ontology |
search-constraints fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
max-depth |
The maximum depth of propagation of the search to federated directories[12]. A negative value indicates that the sender agent is willing to allow the search to propagate across all DFs. |
Optional |
integer |
|
|
max-results |
The maximum number of results to return for the search[13]. A negative value indicates that the sender agent is willing to receive all available results. |
Optional |
integer |
|
|
search-id |
A globally unique identifier for a search. |
Optional |
string |
|
6.1.5 Agent Management System Agent Description
This type of object represents the description of each service registered with the AMS. This is a reification of the Agent Directory Entry from [FIPA00001].
|
Frame Ontology |
ams-agent-description fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
name |
The identifier of the agent. |
Optional |
agent-identifier[14] |
|
|
ownership |
The owner of the agent. |
Optional |
string |
|
|
state |
The life cycle state of the agent. |
Optional |
string |
initiated active suspended waiting transit |
6.1.6 Agent Platform Description
|
Frame Ontology |
ap-description fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
name |
The name of the AP. |
Mandatory |
string |
|
|
ap-services |
The set of services provided by this AP to the resident agents. |
Optional |
Set of ap-service |
|
6.1.7 Agent Service Description
|
Frame Ontology |
ap-service fipa-agent-management |
|
||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
name |
The name of the AP Service. |
Mandatory |
string |
|
|
type |
The type of the AP Service. |
Mandatory |
string |
fipa.mtp.* |
|
addresses |
A list of the addresses of the service. |
Mandatory |
Sequence of url |
|
6.1.8 Property Template
This is a special object that is useful for specifying parameter/value pairs.
|
Frame Ontology |
property fipa-agent-management |
|
|||
|
Parameter |
Description |
Presence |
Type |
Reserved Values |
|
|
name |
The name of the property. |
Mandatory |
string |
|
|
|
value |
The value of the property |
Mandatory |
term |
|
|
6.2 Function Descriptions
The following tables define usage and semantics of the functions that are part of the fipa-agent-management ontology and that are supported by the agent management services and agents on the AP.
This ontology does not specify any specific positional order to encode the parameters of the objects. Therefore, it is required to encode objects in SL by specifying both the parameter name and the parameter value (see Section 3.6 of [FIPA00008]).
The following terms are used to describe the functions of the fipa-agent-management domain:
· Function. This is the symbol that identifies the function in the ontology.
· Ontology. This is the name of the ontology, whose domain of discourse includes the function described in the table.
· Supported by. This is the type of agent that supports this function.
· Description. This is a natural language description of the semantics of the function.
· Domain. This indicates the domain over which the function is defined. The arguments passed to the function must belong to the set identified by the domain.
· Range. This indicates the range to which the function maps the symbols of the domain. The result of the function is a symbol belonging to the set identified by the range.
· Arity. This indicates the number of arguments that a function takes. If a function can take an arbitrary number of arguments, then its arity is undefined.
6.2.1 Registration of an Object with an Agent
|
Function |
register |
|
|
Ontology |
fipa-agent-management |
|
|
Supported by |
DF and AMS |
|
|
Description |
The execution of this function has the effect of registering a new object into the knowledge base of the executing agent. The DF or AMS description supplied must include a valid AID. |
|
|
Domain |
df-agent-description / ams-agent-description |
|
|
Range |
The execution of this function results in a change of the state, but it has no explicit result. Therefore there is no range set. |
|
|
Arity |
1 |
|
6.2.2 Deregistration of an Object with an Agent
|
Function |
deregister |
|
|
Ontology |
fipa-agent-management |
|
|
Supported by |
DF and AMS |
|
|
Description |
An agent may deregister an object in order to remove all of its parameters from a directory. The DF or AMS description supplied must include a valid AID. |
|
|
Domain |
df-agent-description / ams-agent-description |
|
|
Range |
The execution of this function results in a change of the state, but it has no explicit result. Therefore there is no range set. |
|
|
Arity |
1 |
|
6.2.3 Modification of an Object Registration with an Agent
|
Function |
modify |
|
|
Ontology |
fipa-agent-management |
|
|
Supported by |
DF and AMS |
|
|
Description |
An agent may make a modification in order to change its object registration with another agent. The argument of a modify function will replace the existing object description stored within the executing agent. The DF or AMS description supplied must include a valid AID. |
|
|
Domain |
df-agent-description / ams-agent-description |
|
|
Range |
The execution of this function results in a change of the state, but it has no explicit result. Therefore there is no range set. |
|
|
Arity |
1 |
|
6.2.4 Search for an Object Registration with an Agent
|
Function |
search |
|
|
Ontology |
fipa-agent-management |
|
|
Supported by |
DF and AMS |
|
|
Description |
An agent may search for an object template in order to request information from an agent, in particular from a DF or an AMS. A successful search can return one or more agent descriptions that satisfy the search criteria and a null set is returned where no agent entries satisfy the search criteria. The DF or AMS description supplied must include a valid AID. |
|
|
Domain |
df-agent-description / ams-agent-description ´[15] search-constraints |
|
|
Range |
Set of objects. In particular, a set of df-agent-descriptions (for the DF) and a set of ams-agent-descriptions (for the AMS). |
|
|
Arity |
2 |
|
6.2.4.1 Matching Criterion
The search action defined in this ontology mandates the implementation of the following matching criterion in order to determine the set of objects that satisfy the search criteria.
The first thing to note about the matching operation is that the search action receives, as its first argument, an object description that evaluates to a structured object that will be used as an object template during the execution of the search action. In the following explanation, the expressions parameter template and value template are used to denote a parameter of the object template, and the value of the parameter of the object template, respectively.
A registered object matches an object template if:
1. The class name of the object (that is, the object type) is the same as the class name of the object description template, and,
2. Each parameter of the object template is matched by a parameter of the object description.
A parameter matches a parameter template if the parameter name is the same as the template parameter name, and its value matches the value template.
Since the value of a parameter is a term, the rules for a term to match another term template must be given. Before, it must be acknowledged that the values of the parameters of descriptions kept by the AMS or by the DF can only be either a constant, set, sequence (see [FIPA00008]) or other object descriptions (for example, a service-description).
The search action evaluates functional expressions before the object template is matched against the descriptions kept by the AMS or by the DF. This means that if the value of a parameter of an object description is a functional term (for example, (plus 2 3)), then what is seen by the matching process is the result of evaluating the functional term within the context of the receiving agent. A constant matches a constant template if they are equal.
Informally, a sequence matches a sequence template if the elements of the sequence template are matched by elements of the sequence appearing in the same order. Formally, the following recursive rules apply:
1. An empty sequence matches an empty sequence, and,
2. The sequence (cons x sequence1)[16] matches the sequence template (cons y sequence2) if:
· x matches y and sequence1 matches sequence2, or,
· sequence1 matches (cons y sequence2).
Finally, a set matches a set template if each element of the set template is matched by an element of the set template. Notice that it is possible that the same element of the set matches more than one element of the set template.
6.2.4.2 Matching Example
The following DF agent description:
(df-agent‑description
:name
(agent‑identifier
:name cameraproxy1@foo.com
:addresses (sequence iiop://foo.com/acc))
:services (set
(service‑description
:name description‑delivery‑1
:type description‑delivery
:ontologies (set traffic‑surveillance‑domain)
:properties (set
(property
:name camera‑id
:value camera1)
(property
:name baud‑rate
:value 1)))
(service‑description
:name agent‑feedback‑information‑1
:type agent‑feedback‑information
:ontologies (set traffic‑surveillance‑domain)
:properties (set
(property
:name camera‑id
:value camera1))))
:protocols (set fipa-request fipa-query)
:ontologies (set traffic‑surveillance‑domain fipa-agent-management)
:languages (set fipa-sl))
will match the following DF agent description template:
(df-agent‑description
:services (set
(service‑description
:type description‑delivery
:ontologies (set traffic‑surveillance‑domain)
:properties (set
(property
:name camera‑id
:value camera1))
:languages (set fipa-sl fipa-sl1))
Notice that several parameters of the df‑agent‑description were omitted in the df‑agent‑description template. Furthermore, not all elements of set‑valued parameters of the df‑agent‑description were specified and, when the elements of a set were themselves descriptions, the corresponding object description templates are also partial descriptions.
6.2.5 Retrieve an Agent Platform Description
|
Function |
get-description |
|
|
Ontology |
fipa-agent-management |
|
|
Supported by |
AMS |
|
|
Description |
An agent can make a query in order to request the platform profile of an AP from an AMS. |
|
|
Domain |
None |
|
|
Range |
ap-description |
|
|
Arity |
0 |
|
6.3 Exceptions
The normal pattern of interactions between application agents and management agents follow the form of the fipa-request interaction protocol (see [FIPA00026]). Under some circumstances, an exception can be generated, for example, when an AID that has been already registered is re-registered. These exceptions are represented as propositions that evaluate to true under the exceptional circumstances. This section describes the standard set of predicates (defined over a set of arguments) and propositional symbols in the domain of discourse of the fipa-agent-management ontology.
6.3.1 Exception Selection
The following rules are adopted to select the appropriate communicative act that will be returned in when a management action causes an exception:
· If the communicative act is not understood by the receiving agent, then the replied communicative act is not-understood.
· If the requested action is not supported by the receiving agent, then the communicative act is refuse.
· If the requested action is supported by the receiving agent but the sending agent is not authorised to request the function, then the communicative act is refuse.
· If the requested function is supported by the receiving agent and the client agent is authorised to request the function but the function is syntactically or semantically ill-specified, then the communicative act is refuse.
· In all the other cases the receiving agent sends to the sending agent a communicative act of type agree. Subsequently if any condition arises that prevents the receiving agent from successfully completing the requested function, then the communicative act is failure.
6.3.2 Exception Classes
There are four main classes or exceptions that can be generated in response to a management action request:
· unsupported: The communicative act and the content has been understood by the receiving agent, but it is not supported.
· unrecognised: The content has not been understood by the receiving agent.
· unexpected: The content has been understood by the receiving agent, but it includes something that was unexpected.
· missing: The content has been understood by the receiving agent, but something that was expected is missing.
6.3.3 Not Understood Exception Predicates
|
Communicative Act Ontology |
not-understood fipa-agent-management |
|
|
Predicate Symbol |
Arguments |
Description |
|
unsupported-act |
string |
The receiving agent does not support the specific communicative act; the string identifies the unsupported communicative act. |
|
unexpected-act |
string |
The receiving agent supports the specified communicative act, but it is out of context; the string identifies the unexpected communicative act. |
|
unsupported-value |
string |
The receiving agent does not support the value of a message parameter; the string identifies the message parameter name. |
|
unrecognised-value |
string |
The receiving agent cannot recognise the value of a message parameter; the string identifies the message parameter name. |
6.3.4 Refusal Exception Propositions
|
Communicative Act Ontology |
refuse fipa-agent-management |
|
|
Predicate symbol |
Arguments |
Description |
|
unauthorised |
|
The sending agent is not authorised to perform the function. |
|
unsupported-function |
string |
The receiving agent does not support the function; the string identifies the unsupported function name. |
|
missing-argument |
string |
A mandatory function argument is missing; the string identifies the missing function argument name. |
|
unexpected-argument |
string |
A mandatory function argument is present which is not required; the string identifies the function argument that is unexpected. |
|
unexpected-argument-count |
|
The number of function arguments is incorrect. |
|
missing-parameter |
string string |
A mandatory parameter is missing; the first string represents the object name and the second string represents the missing parameter name. |
|
unexpected-parameter |
string string |
The receiving agent does not support the parameter; the first string represents the function name and the second string represents the unsupported parameter name. |
|
unrecognised-parameter-value |
string string |
The receiving agent cannot recognise the value of a parameter; the first string represents the object name and the second string represents the parameter name of the unrecognised parameter value. |
6.3.5 Failure Exception Propositions
|
Communicative Act Ontology |
failure fipa-agent-management |
|
|
Predicate symbol |
Arguments |
Description |
|
already-registered |
|
The sending agent is already registered with the receiving agent. |
|
not-registered |
|
The sending agent is not registered with the receiving agent. |
|
internal-error |
string |
An internal error occurred; the string identifies the internal error. |
7 Agent Management Content Language
Agent Management uses fipa-sl0 as a content language which is defined in [FIPA00008].
8 References
[FIPA00001] FIPA
Abstract Architecture Specification. Foundation for Intelligent Physical
Agents, 2000.
http://www.fipa.org/specs/fipa00001/
[FIPA00008] FIPA SL Content Language Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00008/
[FIPA00025] FIPA Interaction Protocol Library Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00025/
[FIPA00026] FIPA Request Interaction Protocol Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00026/
[FIPA00067] FIPA Agent Message Transport Service Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00067/
[FIPA00079] FIPA Agent Software Integration Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00079/
[RFC2396] Uniform Resource Identifiers: Generic Syntax. Request for Comments, 1992. http://www.ietf.org/rfc/rfc2396.txt
9 Informative Annex A — Dialogue Examples
1. The agent dummy is created and it registers with the AMS of its home AP:
(request
:sender
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name ams@foo.com
:addresses (sequence
iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(ams-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:state active))))")
2. The AMS agrees and then informs dummy of the successful execution of the action:
(agree
:sender
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(ams-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:state active)))
true)")
(inform
:sender
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((done
(action
(agent-identifier
:name ams@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(ams-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:state active)))))")
3. Next, dummy registers its services with the default DF of the AP:
(request
:sender
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:protocols (set fipa-request application-protocol)
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type user-profiling
:ontologies (set meeting-scheduler)
:properties (set
(property
:name learning-algorithm
:value bbn)
(property
:name max-nodes
:value 10000000)))))))))")
4. The AMS agrees and then informs dummy of the successful execution of the action:
(agree
:sender
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc)
(register
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:protocols (set fipa-request application-protocol)
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type user-profiling
:ontologies (set meeting-scheduler)
:properties (set
(property
:name learning-algorithm
:value bbn)
(property
:name max-nodes
:value 10000000)))))))
true)")
(inform
:sender
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((done
(action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(register
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:protocols (set fipa-request application-protocol)
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type user-profiling
:ontologies (set meeting-scheduler)
:properties (set
(property
:name learning-algorithm
:value bbn)
(property
:name max-nodes
:value 10000000))))))))")
5. Then, dummy searches with the DF for a list of meeting scheduler agents:
(request
:sender
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(search
(df-agent-description
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type meeting-scheduler-service)))
(search-constraints
:min-depth 2))))")
(agree
:sender
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(search
(df-agent-description
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type meeting-scheduler-service))
(search-constraint :max-depth 2))))
true)")
(inform
:sender
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((result
(action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(search
(df-agent-description
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type meeting-scheduler-service))
(search-constraint :max-depth 2))))
(set
(df-agent-description
:name
(agent-identifier
:name scheduler-agent@foo.com
:addresses (sequence iiop://foo.com/acc))
:ontologies (set meeting-scheduler fipa-agent-management)
:languages (set fipa-sl0 fipa-sl1 kif)
:services (set
(service-description
:name profiling
:type meeting-scheduler-service)
(service-description
:name profiling
:type user-profiling-service))))))")
6. Now dummy tries to modify the description of scheduler-agent with the DF, but the DF refuses because dummy is not authorised:
(request
:sender
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence (iiop://foo.com/acc))
(modify
(df-agent-description
:name
(agent-identifier
:name scheduler-agent@foo.com
:addresses (sequence iiop://foo.com/acc))
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type meeting-scheduler-service))))))")
(refuse
:sender
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(modify
(df-agent-description
:name
(agent-identifier
:name scheduler-agent@foo.com
:addresses (sequence iiop://foo.com/acc))
:ontologies (set meeting-scheduler)
:languages (set fipa-sl0 kif)
:services (set
(service-description
:name profiling
:type meeting-scheduler-service)))))
unauthorised)")
7. Finally, dummy tries to deregister its description with the DF, but the message is ill-formed and the DF does not understand (because the DF does not understand the propose performative):
(propose
:sender
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(deregister
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))))))")
(not-understood
:sender
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
"((propose
:sender
(agent-identifier
:name dummy@foo.com
:addresses (sequence iiop://foo.com/acc))
:receiver (set
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc)))
:language fipa-sl0
:protocol fipa-request
:ontology fipa-agent-management
:content
\""((action
(agent-identifier
:name df@foo.com
:addresses (sequence iiop://foo.com/acc))
(deregister
(df-agent-description
:name
(agent-identifier
:name dummy@foo.com
:addresses
(sequence iiop://foo.com/acc)))))))\""
(unsupported-act propose)))")
10 Informative Annex B — ChangeLog
10.1 2001/10/03 - version H by FIPA Architecture Board
Page 24, line 825: Changed incorrect reference from AMS to DF
10.2 2002/11/01 - version I by TC X2S
Entire document: Removed all leading : from parameter names
Entire document: Changed all ontology terms to lowercase
Entire document: Various typo changes to all examples
Entire document: Changed references of hap to hap_name
Entire document: Fixed syntax of the examples by adding extra parenthesis in the content
Page 2, line 105: Added a footnote linking agent management services to the Abstract Architecture notion of service
Page 2, lines 108-116: Added a new definition for agent which is compatible with [FIPA00001]
Page 2, line 118: Removed the requirement that the DF is a mandatory component of the AP
Page 2, line 120: Added a link between the DF and the Agent Directory Service from [FIPA00001]
Page 3, line 125: Added a link between the AMS and the Agent Directory Service from [FIPA00001]
Page 3, line 143: Removed obsolete reference to dynamic registration
Page 4, line 151: Restructured section on Agent Naming to list all components of an AID and cross-reference with equivalents in [FIPA00001]
Page 4, line 153: Added a sentence describing AID equivalence
Page 6, line 215: Removed the requirement that the DF is a mandatory component of the AP
Page 6, line 260: Changed incorrect reference to df-search-result to max-results
Page 6, line 261: Added text on limiting the propagation of federated searches
Page 7, lines 265-266: Removed obsolete reference to dynamic registration
Page 7, lines 278-280: Removed sentences describing the requirements that the AMS must check all MTS message sends and receives
Page 7, line 297: Added a link between the name parameter of the AMS and the Service Root from [FIPA00001]
Page 8, line 331: Removed section on Mandatory Functions Supported by Agents (specifically quit)
Page 9, line 345: Added an explanatory sentence to the agent life cycle description
Page 10, lines 414, 427: Removed incorrect reference to [FIPA00005]
Page 11, lines 429-431: Removed obsolete reference to dynamic registration
Page 11, lines 433-435: Removed obsolete references to dynamic registration
Page 11, line 469: Added a section explaining registration lease times
Page 12, line 472: Added a note that references [FIPA00067] for the closure of fipa-agent-management ontology
Page 13, lines 498, 502: Modified the names of the following parameters: protocols, ontologies, languages
Page 13, line 493: Added a link between the addresses parameter and the Locator from [FIPA00001]
Page 13, line 497: Added a link between the df-agent-description and the Agent Directory Entry from [FIPA00001]
Page 13, line 498: Added a footnote requiring at least one AID to be present, except when searching
Page 13, line 498: Changed the plurality of the protocol, ontology and language parameters
Page 13, line 498: Added a new parameter, lease-time, to the df-agent-description
Page 13, line 498: Added a footnote explaining the suggested value of lease-time as a time duration
Page 13, line 498: Added a footnote explaining the default lease time value
Page 13, line 502: Changed the plurality of the protocol, ontology and language parameters
Page 14, line 506: Added a note on negative values for max-depth and max-results
Page 14, line 506: Added a search-id parameter to search-constraints
Page 14, line 509: Added a link between the ams-agent-description and the Agent Directory Entry from [FIPA00001]
Page 14, Line 510: Added a footnote requiring at least one AID to be present, except when searching
Page 14, line 512: Removed mobility parameter from ap-description
Page 14, line 512: Removed dynamic parameter from ap-description
Page 14, line 512: Changed name of transport-profile parameter to ap-service
Page 14, line 512: Changed the plurality of the address parameter
Page 15, line 521: Added note on how to encode objects in SL
Page 14, line 548: Modified search action to handle both ams-agent-description and df-agent-description
Page 17, line 588: Removed the incorrect word ‘template’ at the end of the sentence
Page 17, line 609: Changed 1MHZ to 1 in example
Page 18, line 642: Removed quit function
Page 18, lines 647-649: Changed the exception model from predicates which return true to propositions that evaluate to true