Published in AI Magazine, Volume 11, Number 5, pp 68-70, January 1991 issue.

Knowledge Discovery in Real Databases:
A Report on the IJCAI-89 Workshop

Gregory Piatetsky-Shapiro
Knowledge Based Systems Department
GTE Laboratories Incorporated
40 Sylvan Road, Waltham MA 02254

The growth in the amount of available databases far outstrips the growth of corresponding knowledge. This creates both a need and an opportunity for extracting knowledge from databases. Many recent results have been reported on extracting different kinds of knowledge from databases, including diagnostic rules, drug side effects, classes of stars, rules for expert systems, and rules for semantic query optimization.

The importance of this topic is now recognized by leading researchers. Michie predicts that ``The next area that is going to explode is the use of machine learning tools as a component of large scale data analysis'' (AI Week, March 15, 1990). At a recent NSF invitational workshop on the future of database research (Lagunita, CA, February 1990), ``knowledge mining'' was among the top 5 research topics.

The viability of knowledge discovery is also being recognized by business and government organizations. American Airlines is looking for patterns in its frequent flyer databases. Banks are analyzing credit data to determine better rules for credit assessment and bankruptcy prediction. General Motors is automatically constructing diagnostic expert systems from a database of car trouble symptoms and problems found. The IRS is looking for patterns of tax cheating in its databases. Those are only some of the examples.

Some of the research has matured enough to find its way into commercial systems for rule discovery in databases. Several such systems have appeared recently, including IXL™, NEXTRA™, BEAGLE™, KnowledgeSeeker™, AIM™, and KnowledgeMaker™.

Knowledge discovery in databases is an interesting topic, drawing from several fields including expert systems, machine learning, intelligent databases, knowledge acquisition, case-based reasoning and statistics. The Knowledge Discovery in Databases workshop, held on August 20, 1989 in Detroit, MI, during IJCAI-89, brought together many leading researchers in Machine Learning, Expert Databases, Knowledge Acquisition, Fuzzy Sets, and other areas. The workshop had interesting presentations and lively panel discussion, with lots of interaction. It helped to remove some of the misconceptions that Machine Learning researchers have about databases, i.e., that databases are not just static tables of simple data, but complex entities with transactions, security, and updates. While those researchers just want to use the data, the database people want to integrate the acquired knowledge into the database system. The workshop also helped to educate the database researchers about the available wealth of approaches to machine discovery.

I was the chairman of the workshop. The program committee consisted of Jaime Carbonell, Carnegie Mellon University, William Frawley, GTE Laboratories, Kamran Parsaye, IntelligenceWare, J. Ross Quinlan, University of Sydney, Michael Siegel, Boston University and MIT, and Ramasamy Uthurusamy, GM Research Laboratories.

The workshop generated a significant international interest. We received 69 submissions from 12 countries: USA (39), Canada (9), UK (3), P.R. China (3), Italy (3), France (2), Sweden (2), India (2), Belgium (2), Germany (2), Japan (1), and Australia (1). Thirty nine contributors from 9 countries were invited to attend the workshop. The workshop was also attended by Robert Simpson from DARPA and Y.T. Chien, Director of AI & Robotics at the NSF.

Nine papers were presented in three sessions: Data-Driven Discovery Methods, Knowledge-Based Approaches, and Systems and Applications. The revised versions of the workshop papers will be included in the forthcoming collection on Knowledge Discovery in Databases, to be published by AAAI and MIT press in early 1991, and will not be discussed here.

The workshop concluded with a stimulating panel discussion by Pat Langley, Larry Kerschberg and J. Ross Quinlan.

There was general agreement that Knowledge Discovery is a promising research direction that will become more important as the number of domains for which there are no human experts increases. Applications to large real databases will require algorithms that are efficient and handle uncertainty well. More complex domains demand the use of more expressive (i.e. first-order) languages.

Use of Domain Knowledge in Discovery

There was, however, a spirited disagreement on usage of domain (background) knowledge, which can be defined as any information not explicitly present in the data. Tom Mitchell pointed out that some problems are so large (e.g. molecule segmentation in Meta-Dendral), that you need some domain constraints to limit the search space (e.g. double bonds don't break). Ross Quinlan suggested that if we can design efficient algorithms that search well, we should try to avoid such constraints, because they limit what we can find.

Jaime Carbonell said that he really liked domain constraints, and that in his latest domain --- logistics planning --- the size of search space may be 10300 without constraints like ``Trucks don't drive over water". No system, no matter how efficient, can search a space that large.

Someone pointed out, however, that in the winter trucks can drive over water. This example, in a nutshell, illustrates the utility and pitfalls of using domain knowledge to constrain the search. Use of domain constraints narrows the search, enabling us to tackle larger problems and solve them faster. The danger is that the constraints will prevent the discovery of some unexpected solutions, such as where trucks drive over water. Depending on our objectives, we should be able to play both sides of this trade-off.

Quinlan suggested that it is OK to use domain knowledge verified by the data. Langley said that a good way for dealing with this dilemma is to develop incremental learning systems, that can discover new things and reuse them in discovery, thereby boot-strapping themselves. Such systems can be started with little or no domain knowledge and eventually reach a good level. However, it was pointed out that it took scientists several hundred years to discover the necessary background knowledge for physics and chemistry, so the proposed incremental discovery system may have to run for quite a while.

Good Application Domains

The discussion then turned to what characterizes good domains for knowledge discovery.

Quinlan pointed that in order to learn something you have to almost know it already. A minimum requirement for a good domain is that you have measurements of the important parameters. As an example of a bad domain he gave off-shore oil drilling rigs that collect and send ashore enormous amounts of data, which are just measurements of various things on the platform. Nobody knows whether they are relevant to the production of the platform or not. To go looking in a database like that, which is very large, is probably not a good idea.

The reason medical domains are so appropriate for discovery is that (1) we have medical databases, (2) a considerable medical expertise goes into deciding what is recorded in the databases, and (3) it is very easy to outperform some doctors.

Kerschberg suggested applying discovery to ``Legacy systems". These are old systems, developed in the 60-s and 70-s, using obsolete technology (some are still using punchcards!). The problem arises when the people who have maintained them are no longer available, while the systems still perform a useful business function. There are companies that maintain such legacy systems by doing reverse engineering of the old programs to extract the data model, and then forward engineering the code to transfer the old database into a new system. Such reverse engineering can use whatever knowledge can be discovered from the data itself.

Philip Schrodt from the University of Missouri described the Inter-University Consortium for Political and Social Research, which has about 2000 data sets --- mostly social survey data for the last twenty years. He suggested there is plenty to discover there.

Langley observed that machine learning has had the most success with simple diagnostic tasks. Domains like medical diagnosis, or diagnosis of problems with cars, are where most of the initial high-payoff applications are likely to be.

Barry Silverman suggested that there are many government databases with real discovery problems. For example, IRS databases contain many interesting patterns, although some researchers may not want to work on them on the grounds of the Fifth Amendment. The FBI has many years of records of all airplane crashes. Analysis of this database may contribute to improved safety in the air.

Many corporate databases are also good targets for discovery, with numerous such projects underway. However, the corporations (and especially banks and insurance companies) are not likely to publish if they find something of competitive advantage.

Directions for Future Research

Finally, I asked the panel to describe good and bad directions for future research.

Quinlan said that there are many interesting directions, e.g. incremental algorithms vs batch algorithms, very fast algorithms. Almost anything in this area has some substance. A bad direction is to prove that some algorithm is better than ID3. A more serious example of bad research is trying to show how to squeeze out the last half of one percent of performance.

Langley addressed methodological concerns. He suggested to build on what has been done, before coming up with new algorithms. One should not run a system on a couple of examples and see ``if this is good''. Rather, the discovered knowledge should be brought back into the database to see whether it is useful. Building tightly integrated systems is important as it will force us to generalize our theories.

Langley seconded a call by Bob Simpson for having more tools, tested and documented, made available to other people. (This is the goal of the recently started MACHINE LEARNING TOOLBOX project at the University of Aberdeen in Scotland, UK, run in cooperation with Esprit.) This, of course, will make it easier for other people to run comparative studies. They may show how bad your system is, but that is what science is all about.

Kerschberg took an engineering view. He suggested taking some of the existing algorithms and seeing how they scale up on very large databases. It is not so important how long it takes to discover knowledge, because it can be done off-line. But once the useful knowledge is discovered, it should be brought back into the database in some form, such as integrity rules, semantic optimization rules, or functional dependencies.

Pandora's Box?

An important issue that was only touched at the workshop is the appropriateness of discovery. A careless discovery may open a Pandora's Box of unpleasant surprises.

Some kinds of discovery are actually illegal. The federal and state privacy laws limit what can be discovered about individuals from census data. Use of drug trafficker's ``profiles" by law enforcement agencies has been very controversial and some parts of the profile, such as race, have been ruled illegal.

Political, ethical and moral considerations may affect other discoveries. The FBI proposal for setting up a nationwide database of criminal suspects was shut down after congressional objections on invasion of privacy.

A pattern that involves racial or ethnic characteristic is likely to be controversial. The FDA ban in April 1990 on blood donations by people from Haiti and Sub-Saharan Africa is a good example. The discovered pattern of high incidence of AIDS in those groups was protested as being racially motivated, because there was also a high incidence of AIDS in another geographical group (men from New York and San Francisco), who were not forbidden to donate blood.

However, from the media reports on this controversy it was not clear what is the strength of those patterns, and what additional factors were considered. To avoid purely emotional arguments in such cases it is desirable to give more detailed information such as

Based on a sample of size S, people in group Z have a 33 to 41% likelihood of developing the disease X. P% of all people fall into group Z. The nationwide risk of developing X is 10 to 12%.
This will allow the public a better perception of the pattern and will decrease the controversy.


The workshop confirmed that knowledge discovery in databases is an idea whose time has come. Some of the important research issues addressed in the workshop were: The incremental, interactive discovery methods may transform the static databases of today into evolving information systems of tomorrow. Caution is required for discovery on demographic databases, to avoid findings that are illegal or unethical. Some of the research issues that were little addressed in this workshop, but are likely to become more important in the future are: Finally, discovery systems should be applied to real databases and judged on whether or not they can make useful and significant discoveries. Some successful applications have already been reported and more are on the way!

I am very grateful to the workshop participants for making it all possible. I thank Bud Frawley, Chris Matheus, Larry Kerschberg, and Wray Buntine for their insightful comments on this report, and Shri Goyal for his encouragement. The expressed opinions and mistakes remaining are mine only.