artificial intelligence Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech r ...

, 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 A rational agent or rational being is a person or entity that always aims to perform optimal actions based on given premises and information. A rational agent can be anything that makes decisions, typically a person, firm, machine, or software. Th ...

intelligent agent In artificial intelligence, an intelligent agent (IA) is anything which perceives its environment, takes actions autonomously in order to achieve goals, and may improve its performance with learning or may use knowledge. They may be simple or ...

using the

belief–desire–intention software model The belief–desire–intention software model (BDI) is a software model developed for programming intelligent agents. Superficially characterized by the implementation of an agent's ''beliefs'', ''desires'' and ''intentions'', it actually uses the ...

. A user application is predominately defined, and provided to a PRS system is a set of ''knowledge areas''. Each knowledge area is a piece of

procedural knowledge Procedural knowledge (also known as knowing-how, and sometimes referred to as practical knowledge, imperative knowledge, or performative knowledge) is the knowledge exercised in the performance of some task. Unlike descriptive knowledge (also kno ...

that specifies how to do something, e.g., how to navigate down a corridor, or how to plan a path (in contrast with robotic architectures where the programmer just provides a model of what the states of the world are and how the agent's primitive actions affect them). Such a program, together with a PRS interpreter, is used to control the agent. The interpreter is responsible for maintaining beliefs about the world state, choosing which goals to attempt to achieve next, and choosing which knowledge area to apply in the current situation. How exactly these operations are performed might depend on domain-specific

meta-level Meta (from the Greek μετά, '' meta'', meaning "after" or "beyond") is a prefix meaning "more comprehensive" or "transcending". In modern nomenclature, ''meta''- can also serve as a prefix meaning self-referential, as a field of study or end ...

knowledge areas. Unlike traditional AI planning systems that generate a complete plan at the beginning, and replan if unexpected things happen, PRS interleaves planning and doing actions in the world. At any point, the system might only have a partially specified plan for the future. PRS is based on the BDI or belief–desire–intention framework for intelligent agents. Beliefs consist of what the agent believes to be true about the current state of the world, desires consist of the agent's goals, and intentions consist of the agent's current plans for achieving those goals. Furthermore, each of these three components is typically ''explicitly'' represented somewhere within the memory of the PRS agent at runtime, which is in contrast to purely reactive systems, such as the

subsumption architecture Subsumption architecture is a reactive robotic architecture heavily associated with behavior-based robotics which was very popular in the 1980s and 90s. The term was introduced by Rodney Brooks and colleagues in 1986.Brooks, R. A., "A Robust Progr ...

History

The PRS concept was developed by the

Artificial Intelligence Center The Artificial Intelligence Center is a laboratory in the Information and Computing Sciences Division of SRI International. It was founded in 1966 by Charles Rosen and studies artificial intelligence. One of their early projects was Shakey the Robo ...

SRI International SRI International (SRI) is an American nonprofit scientific research institute and organization headquartered in Menlo Park, California. The trustees of Stanford University established SRI in 1946 as a center of innovation to support economic ...

during the 1980s, by many workers including Michael Georgeff, Amy L. Lansky, and François Félix Ingrand. Their framework was responsible for exploiting and popularizing the BDI model in software for control of an

. The seminal application of the framework was a fault detection system for the reaction control system of the

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

Space Shuttle Discovery Space Shuttle ''Discovery'' ( Orbiter Vehicle Designation: OV-103) is one of the orbiters from NASA's Space Shuttle program and the third of five fully operational orbiters to be built. Its first mission, STS-41-D, flew from August 30 to S ...

. Development on this PRS continued at the

Australian Artificial Intelligence Institute In Australia, the Australian Artificial Intelligence Institute (Australian AI Institute, AAII, or A2I2) was a government-funded research and development laboratory for investigating and commercializing Artificial Intelligence, specifically Intel ...

through to the late 1990s, which led to the development of a

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

implementation and extension called dMARS.

Architecture

The system architecture of SRI's PRS includes the following components: * Database for beliefs about the world, represented using first order predicate calculus. * Goals to be realized by the system as conditions over an interval of time on internal and external state descriptions (desires). * Knowledge areas (KAs) or plans that define sequences of low-level actions toward achieving a goal in specific situations. * Intentions that include those KAs that have been selected for current and eventual execution. * Interpreter or inference mechanism that manages the system.

Features

SRI's PRS was developed for embedded application in dynamic and real-time environments. As such it specifically addressed the limitations of other contemporary control and reasoning architectures like expert systems and the

blackboard system A blackboard system is an artificial intelligence approach based on the blackboard architectural model, where a common knowledge base, the "blackboard", is iteratively updated by a diverse group of specialist knowledge sources, starting with a pro ...

. The following define the general requirements for the development of their PRS: * asynchronous event handling * guaranteed reaction and response types * procedural representation of knowledge * handling of multiple problems * reactive and goal-directed behavior * focus of attention * reflective reasoning capabilities * continuous embedded operation * handling of incomplete or inaccurate data * handling of transients * modeling delayed feedback * operator control

Applications

The seminal application of SRI's PRS was a monitoring and fault detection system for the reaction control system (RCS) on the NASA space shuttle. The RCS provides propulsive forces from a collection of jet thrusters and controls altitude of the space shuttle. A PRS-based fault diagnostic system was developed and tested using a simulator. It included over 100 KAs and over 25 meta level KAs. RCS specific KAs were written by space shuttle mission controllers. It was implemented on the Symbolics 3600 Series LISP machine and used multiple communicating instances of PRS. The system maintained over 1000 facts about the RCS, over 650 facts for the forward RCS alone and half of which are updated continuously during the mission. A version of the PRS was used to monitor the reaction control system on the

. PRS was tested on

Shakey the robot Shakey the Robot was the first general-purpose mobile robot able to reason about its own actions. While other robots would have to be instructed on each individual step of completing a larger task, Shakey could analyze commands and break them down ...

including navigational and simulated jet malfunction scenarios based on the space shuttle. Later applications included a network management monitor called the Interactive Real-time Telecommunications Network Management System (IRTNMS) for

Telecom Australia Telstra Group Limited is an Australian telecommunications company that builds and operates telecommunications networks and markets voice, mobile, internet access, pay television and other products and services. It is a member of the S&P/ASX 20 ...

Extensions

The following list the major implementations and extensions of the PRS architecture. * UM-PRS * OpenPRS (formerly C-PRS and Propice) * AgentSpeak * Distributed Multi-Agent Reasoning System (dMARS) * GORITE * JAM * JACK Intelligent Agents * SRI Procedural Agent Realization Kit (SPARK) * PRS-CL

References

{{reflist

External links

PRS-CL: A Procedural Reasoning System
An extension to PRS maintained by SRI International Knowledge representation Cognitive architecture Agent-based software Multi-agent systems Agent-oriented programming languages Agent-based programming languages SRI International software