| Dr. Robert (Bob) L. Simpson, Jr., is Vice President and Chief Scientist at ASI. Bob has over 40 years experience in computer research and development and applied artificial intelligence. His Ph.D. thesis at Georgia Tech in 1985 was the first thesis to define the Case-Based Reasoning process and describe its use in a problem solving situation. | |
Q: What is case-based reasoning? A: Case-based reasoning (CBR), broadly construed, is the process of solving new problems based on the solutions of similar past problems. An auto mechanic who fixes an engine by recalling another car that exhibited similar symptoms is using case-based reasoning. A lawyer who advocates a particular outcome in a trial based on legal precedents or a judge who creates case law is using case-based reasoning. So, too, an engineer copying working elements of nature is treating nature as a database of solutions to problems. Case-based reasoning is analogy plus adaptation. It has been argued that case-based reasoning is not only a powerful method for computer reasoning, but also a pervasive behavior in everyday human problem solving. Or, more radically, that all reasoning is based on past cases experienced or accepted by a problem solver actively exercising choice - prototype theory - most deeply explored in human cognitive science. BACK TO TOP Q: What is so special about case-based reasoning? A: In case-based reasoning (CBR) systems expertise is embodied in a library of past cases, rather than being encoded in classical rules. Each case typically contains a description of the problem, plus a solution and/or the outcome. The knowledge and reasoning process used by an expert to solve the problem can be implicit in the solution or explicitly recorded as another component that can be reused (this is known as "derivational analogy.") To solve a current problem: the problem is matched against the cases in the case base, and similar cases are retrieved. The retrieved cases are used to suggest a solution which is reused and tested for success. If necessary, the solution is then revised. Finally the current problem and the final solution are retained as part of a new case. Many people like case-based reasoning because they feel happier with examples rather than conclusions separated from their context. A case library can also be a powerful corporate knowledge resource, allowing everyone in an organization to tap into the corporate case library when handling a new problem. Since the 1990's CBR has grown into a field of widespread interest, both from an academic and a commercial standpoint. Mature tools and application-focused conferences exist. BACK TO TOP Q: How does case-based reasoning work? A: Case-based reasoning has been formalized for purposes of computer reasoning as a four-step process:  | Retrieve: Given a target problem, retrieve cases from memory that are relevant to solving it. A case consists of a problem, its solution, and, typically, annotations about how the solution was derived. For example, suppose Fred wants to prepare blueberry pancakes. Being a novice cook, the most relevant experience he can recall is one in which he successfully made plain pancakes. The procedure he followed for making the plain pancakes, together with justifications for decisions made along the way, constitutes Fred's retrieved case. | | | Reuse: Map the solution from the previous case to the target problem. This may involve adapting the solution as needed to fit the new situation. In the pancake example, Fred must adapt his retrieved solution to include the addition of blueberries. | | | Revise: Having mapped the previous solution to the target situation, test the new solution in the real world (or a simulation) and, if necessary, revise. This step is often referred to as adaptation. Suppose Fred adapted his pancake solution by adding blueberries to the batter. After mixing, he discovers that the batter has turned blue - an undesired effect. This suggests the following revision: delay the addition of blueberries until after the batter has been ladled into the pan. | | | Retain: After the solution has been successfully adapted to the target problem, store the resulting experience as a new case in memory. It is in this way that the system acquires new cases and is said to learn. Fred, accordingly, records his newfound procedure for making blueberry pancakes, thereby enriching his set of stored experiences, and better preparing him for future pancake-making demands. | BACK TO TOP Q: What types of problems are amenable to case-based reasoning? A: Some of the characteristics of a domain that indicate that a CBR approach might be suitable include: | | Records of previously solved problems exist | | | Historical cases are viewed as an asset which ought to be preserved | | | Remembering previous experiences is useful | | | Specialists talk about their domain by giving examples | | | Experience is at least as valuable as textbook knowledge | Case-based reasoning is often used where experts find it hard to articulate their thought processes when solving problems. This is because knowledge acquisition for a classical KBS would be extremely difficult in such domains, and is likely to produce incomplete or inaccurate results. When using case-based reasoning, the need for knowledge acquisition can be limited to establishing how to characterize cases. Case-based reasoning allows the case-base to be developed incrementally, while maintenance of the case library is relatively easy and can be carried out by domain experts. BACK TO TOP Q: What are some examples of successful case-based reasoning applications? A: Case based reasoning first appeared in commercial tools in the early 1990's and since then has been used to create numerous applications in a wide range of domains: | | Diagnosis: case-based diagnosis systems try to retrieve past cases whose symptom lists are similar in nature to that of the new case and suggest diagnoses based on the best matching retrieved cases. The majority of installed systems are of this type and there are many medical CBR diagnostic systems. | | | Help Desk: case-based diagnostic systems are used in the customer service area dealing with handling problems with a product or service. | | | Assessment: case-based systems are used to determine values for variables by comparing it to the known value of something similar. Assessment tasks are quite common in the finance and marketing domains. | | | Decision support: in decision making, when faced with a complex problem, people often look for analogous problems for possible solutions. CBR systems have been developed to support in this problem retrieval process (often at the level of document retrieval) to find relevant similar problems. CBR is particularly good at querying structured, modular and non-homogeneous documents. | | | Design: Systems to support human designers in architectural and industrial design have been developed. These systems assist the user in only one part of the design process, that of retrieving past cases, and would need to be combined with other forms of reasoning to support the full design process. | BACK TO TOP Q: Who invented case-based reasoning? A: Roger Schank's group at Yale University in the early eighties produced both a cognitive model for CBR and the first CBR applications based upon this model. Janet Kolodner developed the first CBR system called CYRUS. CYRUS contained knowledge, as cases, of the travels and meetings of ex-US Secretary-of-State Cyrus Vance. CYRUS was an implementation of Schank's dynamic memory model. Its case base or episodic memory model later served as the basis for several other CBR systems including MEDIATOR [Simpson, 85], CHEF [Hammond, 86], PERSUADER [Sycara, 87], CASEY [Koton, 89] and JULIA [Hinrichs, 92]. The first AI papers containing the term "case-based reasoning" appeared in 1984 and the first Ph.D. thesis with the term "case-based reasoning" in its title was by Simpson in 1985. BACK TO TOP Q: Can you recommend a good book on case-based reasoning? A: I recommend Janet Kolodner's book "Case-Based Reasoning" published by Morgan Kaufmann in 1993. There are several other good texts as well. BACK TO TOP |
