Editing Knowledge-based systems (section)

==Aspects and development of early systems==
===Knowledge-based vs. expert systems===
{{see also|Expert system}}
The term "knowledge-based system" was often used interchangeably with "[[expert system]]", possibly because almost all of the earliest knowledge-based systems were designed for expert tasks. However, these terms tell us about different aspects of a system:
* ''expert'': describes only the task the system is designed for – its purpose is to aid replace a human expert in a task typically requiring specialised knowledge
* ''knowledge-based'': refers only to the system's architecture –  it represents knowledge explicitly, rather than as procedural code

Today, virtually all expert systems are knowledge-based, whereas knowledge-based system architecture is used in a wide range of types of system designed for a variety of tasks.

===Rule-based systems===
{{main|Rule-based system}}
The first knowledge-based systems were primarily rule-based expert systems. These represented facts about the world as simple assertions in a flat [[database]] and used domain-specific rules to reason about these assertions, and then to add to them. One of the most famous of these early systems was [[Mycin]], a program for medical diagnosis. 

Representing knowledge explicitly via rules had several advantages:
# ''Acquisition and maintenance.'' Using rules meant that domain experts could often define and maintain the rules themselves rather than via a programmer.
# ''Explanation.'' Representing knowledge explicitly allowed systems to reason about how they came to a conclusion and use this information to explain results to users. For example, to follow the chain of inferences that led to a diagnosis and use these facts to explain the diagnosis. 
# ''Reasoning.'' Decoupling the knowledge from the processing of that knowledge enabled general purpose inference engines to be developed. These systems could develop conclusions that followed from a data set that the initial developers may not have even been aware of.<ref>{{Cite book |last=Hayes-Roth |first=Frederick |url=https://archive.org/details/buildingexpertsy00temd |title=Building Expert Systems |last2=Donald Waterman |last3=Douglas Lenat |publisher=Addison-Wesley |year=1983 |isbn=0-201-10686-8}}</ref>

===Meta-reasoning===
Later{{when?|date=May 2024}} architectures for knowledge-based reasoning, such as the BB1 blackboard architecture (a [[blackboard system]]),<ref>{{Cite book |last=Hayes-Roth |first=Barbara |author-link=Barbara Hayes-Roth |url=https://dl.acm.org/citation.cfm?id=892336 |title=BB1: an Architecture for Blackboard Systems that Control, Explain, and Learn about Their Own Behavior |last2=Department |first2=Stanford University Computer Science |date=1984 |publisher=Department of Computer Science, Stanford University}}</ref> allowed the reasoning process itself to be affected by new inferences, providing meta-level reasoning. BB1 allowed the problem-solving process itself to be monitored. Different kinds of problem-solving (e.g., top-down, bottom-up, and opportunistic problem-solving) could be selectively mixed based on the current state of problem solving. Essentially, the problem-solver was being used both to solve a domain-level problem along with its own control problem, which could depend on the former. 

Other examples of knowledge-based system architectures supporting meta-level reasoning are MRS<ref>{{Cite journal |last=Genesereth |first=Michael R |title=1983 - An Overview of Meta-Level Architecture |journal=AAAI-83 Proceedings |page=6}}</ref> and [[Soar (cognitive architecture)|SOAR]].

===Widening of application===
In the 1980s and 1990s, in addition to expert systems, other applications of knowledge-based systems included real-time process control,<ref>{{Cite journal |last=Larsson |first=Jan Eric |last2=Hayes-Roth |first2=Barbara |author-link2=Barbara Hayes-Roth |date=1998 |title=Guardian: An Intelligent Autonomous Agent for Medical Monitoring and Diagnosis |url=http://dblp.uni-trier.de/rec/bibtex/journals/expert/LarssonH98 |journal=IEEE Intelligent Systems |volume=13 |issue=1 |access-date=2012-08-11}}</ref> intelligent tutoring systems,<ref>{{Cite book |last=Clancey |first=William |title=Knowledge-Based Tutoring: The GUIDON Program |date=1987 |publisher=The MIT Press |location=Cambridge, Massachusetts}}</ref> and problem-solvers for specific domains such as protein structure analysis,<ref>{{Cite conference |last=Hayes-Roth |first=Barbara |author-link=Barbara Hayes-Roth |last2=Buchanan |first2=Bruce G. |last3=Lichtarge |first3=Olivier |last4=Hewitt |first4=Mike |last5=Altman |first5=Russ B. |last6=Brinkley |first6=James F. |last7=Cornelius |first7=Craig |last8=Duncan |first8=Bruce S. |last9=Jardetzky |first9=Oleg |date=1986 |title=PROTEAN: Deriving Protein Structure from Constraints |url=http://dblp.uni-trier.de/rec/bibtex/conf/aaai/Hayes-RothBLHABCDJ86 |conference=AAAI |pages=904–909 |access-date=2012-08-11}}</ref> construction-site layout,<ref>{{Cite book |editor=Robert Engelmore |display-editors=et al|title=Blackboard Systems |date=1988 |publisher=Addison-Wesley Pub (Sd)}}</ref> and computer system fault diagnosis.<ref>{{Cite conference |last=Bennett |first=James S. |date=1981 |title=DART: An Expert System for Computer Fault Diagnosis |conference=IJCAI}}</ref>

===Advances driven by enhanced architecture===
As knowledge-based systems became more complex, the techniques used to represent the knowledge base became more sophisticated and included logic, term-rewriting systems, conceptual graphs, and [[Frame (artificial intelligence)|frames]]. 

Frames, for example, are a way representing world knowledge using techniques that can be seen as analogous to [[object-oriented programming]], specifically classes and subclasses, hierarchies and relations between classes, and behavior{{clarify|date=May 2024}} of objects. With the knowledge base more structured, reasoning could now occur not only by independent rules and logical inference, but also based on interactions within the knowledge base itself. For example, procedures stored as [[Daemon (computing)|daemons]] on{{clarify|date=May 2024}} objects could fire and could replicate the chaining behavior of rules.<ref>{{Cite journal |last=Mettrey |first=William |year=1987 |title=An Assessment of Tools for Building Large Knowledge- BasedSystems |url=http://www.aaai.org/ojs/index.php/aimagazine/article/viewArticle/625 |url-status=dead |journal=AI Magazine |volume=8 |issue=4 |archive-url=https://web.archive.org/web/20131110022104/http://www.aaai.org/ojs/index.php/aimagazine/article/viewArticle/625 |archive-date=2013-11-10 |access-date=2013-11-10}}</ref>

===Advances in automated reasoning===
Another advancement in the 1990s was the development of special purpose automated reasoning systems called [[Deductive classifier|classifiers]]. Rather than statically declare the subsumption relations in a knowledge-base, a classifier allows the developer to simply declare facts about the world and let the classifier deduce the relations. In this way a classifier also can play the role of an inference engine.<ref>{{Cite journal |last=MacGregor |first=Robert |date=June 1991 |title=Using a description classifier to enhance knowledge representation |journal=IEEE Expert |volume=6 |issue=3 |pages=41–46 |doi=10.1109/64.87683 |s2cid=29575443}}</ref>

The most recent{{as of?|date=May 2024}} advancement of knowledge-based systems was to adopt the technologies, especially a kind of logic called [[description logic]], for the development of systems that use the internet. The internet often has to deal with complex, [[unstructured data]] that cannot be relied on to fit a specific data model. The technology of knowledge-based systems, and especially the ability to classify objects on demand, is ideal for such systems. The model for these kinds of knowledge-based internet systems is known as the [[Semantic Web]].<ref>{{Cite journal |last=Berners-Lee |first=Tim |last2=James Hendler |last3=Ora Lassila |date=May 17, 2001 |title=The Semantic Web A new form of Web content that is meaningful to computers will unleash a revolution of new possibilities |url=http://www.cs.umd.edu/~golbeck/LBSC690/SemanticWeb.html |url-status=dead |journal=Scientific American |volume=284 |pages=34–43 |doi=10.1038/scientificamerican0501-34 |archive-url=https://web.archive.org/web/20130424071228/http://www.cs.umd.edu/~golbeck/LBSC690/SemanticWeb.html |archive-date=April 24, 2013}}</ref>