The belief–desire–intention software model (BDI) is a
software model developed for programming
intelligent agent
In artificial intelligence, an intelligent agent is an entity that Machine perception, perceives its environment, takes actions autonomously to achieve goals, and may improve its performance through machine learning or by acquiring knowledge r ...
s. Superficially characterized by the implementation of an agent's ''beliefs'', ''desires'' and ''intentions'', it actually uses these concepts to solve a particular problem in agent programming. In essence, it provides a mechanism for separating the activity of selecting a plan (from a plan
library
A library is a collection of Book, books, and possibly other Document, materials and Media (communication), media, that is accessible for use by its members and members of allied institutions. Libraries provide physical (hard copies) or electron ...
or an external planner application) from the execution of currently active plans. Consequently, BDI agents are able to balance the time spent on deliberating about plans (choosing what to do) and executing those plans (doing it). A third activity, creating the plans in the first place (
planning
Planning is the process of thinking regarding the activities required to achieve a desired goal. Planning is based on foresight, the fundamental capacity for mental time travel. Some researchers regard the evolution of forethought - the cap ...
), is not within the scope of the model, and is left to the system designer and programmer.
Overview
In order to achieve this separation, the BDI software model implements the principal aspects of
Michael Bratman's
theory of human practical reasoning (also referred to as Belief-Desire-Intention, or BDI). That is to say, it implements the notions of belief, desire and (in particular) intention, in a manner inspired by Bratman.
For Bratman, desire and intention are both pro-attitudes (mental attitudes concerned with action). He identifies commitment as the distinguishing factor between desire and intention, noting that it leads to (1) temporal persistence in plans and (2) further plans being made on the basis of those to which it is already committed. The BDI software model partially addresses these issues. Temporal persistence, in the sense of explicit reference to time, is not explored. The hierarchical nature of plans is more easily implemented: a plan consists of a number of steps, some of which may invoke other plans. The hierarchical definition of plans itself implies a kind of temporal persistence, since the overarching plan remains in effect while subsidiary plans are being executed.
An important aspect of the BDI software model (in terms of its research relevance) is the existence of logical models through which it is possible to define and reason about BDI agents. Research in this area has led, for example, to the
axiomatization
In mathematics and logic, an axiomatic system is a set of formal statements (i.e. axioms) used to logically derive other statements such as lemmas or theorems. A proof within an axiom system is a sequence of deductive steps that establishes ...
of some BDI implementations, as well as to
formal logical descriptions such as Anand Rao and
Michael Georgeff's BDICTL. The latter combines a
multiple-modal logic (with modalities representing beliefs, desires and intentions) with the
temporal logic
In logic, temporal logic is any system of rules and symbolism for representing, and reasoning about, propositions qualified in terms of time (for example, "I am ''always'' hungry", "I will ''eventually'' be hungry", or "I will be hungry ''until'' I ...
CTL*. More recently, Michael Wooldridge has extended BDICTL to define LORA (the Logic Of Rational Agents), by incorporating an action logic. In principle, LORA allows reasoning not only about individual agents, but also about communication and other interaction in a
multi-agent system
A multi-agent system (MAS or "self-organized system") is a computerized system composed of multiple interacting intelligent agents.H. Pan; M. Zahmatkesh; F. Rekabi-Bana; F. Arvin; J. HuT-STAR: Time-Optimal Swarm Trajectory Planning for Quadroto ...
.
The BDI software model is closely associated with intelligent agents, but does not, of itself, ensure all the characteristics associated with such agents. For example, it allows agents to have private beliefs, but does not force them to be private. It also has nothing to say about agent communication. Ultimately, the BDI software model is an attempt to solve a problem that has more to do with plans and planning (the choice and execution thereof) than it has to do with the programming of intelligent agents. This approach has recently been proposed by
Steven Umbrello and
Roman Yampolskiy
Roman Vladimirovich Yampolskiy (; born in Riga, 13 August 1979) is a Latvian computer scientist at the University of Louisville, mostly known for his work on AI safety and cybersecurity. He holds a PhD from the University at Buffalo (2008). He ...
as a means of designing
autonomous vehicles for human values.
BDI agents
A BDI agent is a particular type of
bounded rational software agent, imbued with particular ''mental attitudes'', viz: Beliefs, Desires and Intentions (BDI).
Architecture
This section defines the idealized architectural components of a BDI system.
* Beliefs: Beliefs represent the informational state of the agent–its beliefs about the world (including itself and other agents). Beliefs can also include
inference rule
Rules of inference are ways of deriving conclusions from premises. They are integral parts of formal logic, serving as norms of the logical structure of valid arguments. If an argument with true premises follows a rule of inference then the co ...
s, allowing
forward chaining
Forward chaining (or forward reasoning) is one of the two main methods of reasoning when using an inference engine and can be described logically as repeated application of ''modus ponens''. Forward chaining is a popular implementation strategy f ...
to lead to new beliefs. Using the term ''belief'' rather than ''knowledge'' recognizes that what an agent believes may not necessarily be true (and in fact may change in the future).
** Beliefset: Beliefs are stored in
database
In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...
(sometimes called a ''belief base'' or a ''belief set''), although that is an
implementation
Implementation is the realization of an application, execution of a plan, idea, scientific modelling, model, design, specification, Standardization, standard, algorithm, policy, or the Management, administration or management of a process or Goal ...
decision.
* Desires: Desires represent the motivational state of the agent. They represent objectives or situations that the agent ''would like'' to accomplish or bring about. Examples of desires might be: ''find the best price'', ''go to the party'' or ''become rich''.
** Goals: A goal is a desire that has been adopted for active pursuit by the agent. Usage of the term ''goals'' adds the further restriction that the set of active desires must be consistent. For example, one should not have concurrent goals to go to a party and to stay at home – even though they could both be desirable.
* Intentions: Intentions represent the deliberative state of the agent – what the agent ''has chosen'' to do. Intentions are desires to which the agent has to some extent committed. In implemented systems, this means the agent has begun executing a plan.
** Plans: Plans are sequences of actions (recipes or knowledge areas) that an agent can perform to achieve one or more of its intentions. Plans may include other plans: my plan to go for a drive may include a plan to find my car keys. This reflects that in Bratman's model, plans are initially only partially conceived, with details being filled in as they progress.
* Events: These are triggers for reactive activity by the agent. An event may update beliefs, trigger plans or modify goals. Events may be generated externally and received by sensors or integrated systems. Additionally, events may be generated internally to trigger decoupled updates or plans of activity.
BDI was also extended with an obligations component, giving rise to the BOID agent architecture to incorporate obligations, norms and commitments of agents that act within a social environment.
BDI interpreter
This section defines an idealized BDI interpreter that provides the basis of SRI's
PRS lineage of BDI systems:
# initialize-state
# repeat
## options: option-generator (event-queue)
## selected-options: deliberate(options)
## update-intentions(selected-options)
## execute()
## get-new-external-events()
## drop-unsuccessful-attitudes()
## drop-impossible-attitudes()
# end repeat
Limitations and criticisms
The BDI software model is one example of a reasoning architecture for a single rational agent, and one concern in a broader
multi-agent system
A multi-agent system (MAS or "self-organized system") is a computerized system composed of multiple interacting intelligent agents.H. Pan; M. Zahmatkesh; F. Rekabi-Bana; F. Arvin; J. HuT-STAR: Time-Optimal Swarm Trajectory Planning for Quadroto ...
. This section bounds the scope of concerns for the BDI software model, highlighting known limitations of the architecture.
* Learning: BDI agents lack any specific mechanisms within the architecture to learn from past behavior and adapt to new situations.
* Three attitudes: Classical
decision theorists and planning research questions the necessity of having all three attitudes,
distributed AI research questions whether the three attitudes are sufficient.
* Logics: The multi-modal logics that underlie BDI (that do not have complete axiomatizations and are not efficiently computable) have little relevance in practice.
* Multiple agents: In addition to not explicitly supporting learning, the framework may not be appropriate to learning behavior. Further, the BDI model does not explicitly describe mechanisms for interaction with other agents and integration into a
multi-agent system
A multi-agent system (MAS or "self-organized system") is a computerized system composed of multiple interacting intelligent agents.H. Pan; M. Zahmatkesh; F. Rekabi-Bana; F. Arvin; J. HuT-STAR: Time-Optimal Swarm Trajectory Planning for Quadroto ...
.
* Explicit goals: Most BDI implementations do not have an explicit representation of goals.
* Lookahead: The architecture does not have (by design) any lookahead deliberation or forward planning. This may not be desirable because adopted plans may use up limited resources, actions may not be reversible, task execution may take longer than forward planning, and actions may have undesirable side effects if unsuccessful.
BDI agent implementations
'Pure' BDI
*
Procedural Reasoning System
In artificial intelligence, a procedural reasoning system (PRS) is a framework for constructing real-time reasoning systems that can perform complex tasks in dynamic environments. It is based on the notion of a rational agent or intelligent agent ...
(PRS)
* IRMA (not implemented but can be considered as PRS with non-reconsideration)
* UM-PRS
* OpenPRS
*
Distributed Multi-Agent Reasoning System (dMARS)
*
AgentSpeak(L) – see Jason below
* AgentSpeak(RT)
[Vikhorev, K., Alechina, N. and Logan, B. (2011)]
"Agent programming with priorities and deadlines"
. In Proceedings of the Tenth International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2011). Taipei, Taiwan. May 2011., pp. 397-404.
* Agent Real-Time System (ARTS) (ARTS)
[Vikhorev, K., Alechina, N. and Logan, B. (2009)]
"The ARTS Real-Time Agent Architecture"
. In Proceedings of Second Workshop on Languages, Methodologies and Development Tools for Multi-agent Systems (LADS2009). Turin, Italy. September 2009. CEUR Workshop Proceedings Vol-494.
* JAM
*
JACK Intelligent Agents
* JADEX (open source project)
*JaKtA
* JASON
*
GORITE
* SPARK
*
3APL
*
2APL
*
GOAL agent programming language
* CogniTAO (Think-As-One)
[CogniTAO (Think-As-One)](_blank)
/ref>[TAO: A JAUS-based High-Level Control System for Single and Multiple Robots Y. Elmaliach, CogniTeam, (2008) ]
* Living Systems Process Suite[Living Systems Process Suite](_blank)
/ref>[Rimassa, G., Greenwood, D. and Kernland, M. E., (2006)]
The Living Systems Technology Suite: An Autonomous Middleware for Autonomic Computing
. International Conference on Autonomic and Autonomous Systems (ICAS).
* PROFETA
* Gwendolen (Part of the Model Checking Agent Programming Languages Framework)
Extensions and hybrid systems
* JACK Teams
* CogniTAO (Think-As-One)
* Living Systems Process Suite
* Brahms
* JaCaMo
See also
* Action selection
Action selection is a way of characterizing the most basic problem of intelligent systems: what to do next. In artificial intelligence and computational cognitive science, "the action selection problem" is typically associated with intelligent ...
* Artificial intelligence
Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...
* Belief–desire–intention model
For popular psychology, the belief–desire–intention (BDI) model of human practical reasoning was developed by Michael Bratman as a way of explaining future-directed intention.
BDI is fundamentally reliant on folk psychology
Folk psycholog ...
* Belief revision
Belief revision (also called belief change) is the process of changing beliefs to take into account a new piece of information. The formal logic, logical formalization of belief revision is researched in philosophy, in databases, and in artifici ...
* Intelligent agent
In artificial intelligence, an intelligent agent is an entity that Machine perception, perceives its environment, takes actions autonomously to achieve goals, and may improve its performance through machine learning or by acquiring knowledge r ...
* Reasoning
Reason is the capacity of consciously applying logic by drawing valid conclusions from new or existing information, with the aim of seeking the truth. It is associated with such characteristically human activities as philosophy, religion, scien ...
* Software agent
In computer science, a software agent is a computer program that acts for a user or another program in a relationship of agency.
The term ''agent'' is derived from the Latin ''agere'' (to do): an agreement to act on one's behalf. Such "action on ...
Notes
References
* A. S. Rao and M. P. Georgeff
Modeling Rational Agents within a BDI-Architecture
In Proceedings of the 2nd International Conference on Principles of Knowledge Representation and Reasoning, pages 473–484, 1991.
* A. S. Rao and M. P. Georgeff
BDI-agents: From Theory to Practice
, In Proceedings of the First International Conference on Multiagent Systems (ICMAS'95), San Francisco, 1995.
*
*
* K. S. Vikhorev, N. Alechina, and B. Logan
The ARTS Real-Time Agent Architecture
In Proceedings of Second Workshop on Languages, Methodologies and Development Tools for Multi-agent Systems (LADS2009). CEUR Workshop Proceedings, Vol-494, Turin, Italy, 2009.
{{DEFAULTSORT:Belief-Desire-Intention Software Model
Artificial intelligence engineering
Belief revision
Agent-based programming languages