Introduction to
Logic Programming

Lessons Sierra Tools Examples Piazza

Week 3

We have now begun our look at queries, but we have not yet finished. We have another week to go before moving on to more interesting topics.

Chapters 3 gives precise definitions for the syntax and semantics of queries. If you want to know the answers to a query or the results of executing an update, you just need to think about the instances of the constituent rules and apply the definitions given in the chapters.

Although these definitions are simple and precise mathematically, they are not exactly satisfying from a computational point of view. The number of instances of query rules can be extremely large, even for finite Herbrand universes; and, of course, there are infinitely many instances for infinite Herbrand universes. The good news is that, in many case, we can get by with with much less work.

This week, we look at ways to do these computations without enumerating all instances. In Chapter 5, we introduce the algorithm used by the Epilog / Sierra interpreter in answering queries. The algorithm is guaranteed to produce the same answers as our instance-based semantics but operates much more efficiently. In Chapter 6, we talk about ways we can take advantage of this algorithm in optimizing queries to get answers even more efficiently.

Your solutions to Assignments 2.1 - 2.3 are due by midnight this coming Sunday. (1) Note that you will likely have trouble doing Assignment 2.3 without using some of the optimization techniques discussed in Chapter 6. (2) You may also need to enlarge Sierra's "query depth" on the Settings menu, as this problem has quite a large search space. (3) Finally, if you are having trouble, you should consider working on a simplified version of the problem before tackling the entire problem. For example, you might start with a two column cryptarithmetic puzzle.

No class this Thursday

The annual FutureLaw conference will take place on April 8, and several of us need to attend. If you like, you can drop in for any or all of the conference. Click here for details. Registration is required, but the conference is free.

FutureLaw is an annual conference on Legal Technology. It brings together researchers, engineers, entrepreneurs, lawyers, investors, and policy makers from around the world to share ideas about the cutting edge of Legal Technology. It is the best known conference of its type in the world.

The conference this year will have even more relevance to CS and AI than usual. (1) The keynote speaker will be Alan Kay, a legend in CS, winner of virtually every CS award (the Kyoto Prize, the Draper Prize, Turing Award), and a great speaker. (2) Also, this year there will be a major award closely related to Logic Programming.

Week 2

By this point, you should have mastered the material in Chapters 1 and 2. From Chapter 1, you should be familiar with the basic idea of Logic Programming - logic programs as runnable specifications. From Chapter 2, you should understand the concept of datasets and some of the issues involved in creating datasets to describe application areas. In fact, you should be more than familiar with this material - ideally, you should be saying to yourself (and others) that, when all is said and done, this stuff is pretty easy. In fact, it *is* easy. But it is also very important, as we use datasets not just for practical purposes but also in defining the semantics of more complex notions to come.

Judging by the discussion on the Forum, it appears that, for many of you, the toughest part of the first assignment set was figuring out how to use the meta-vocabulary of types and predicates and attributes to describe types and predicates and attributes. Most of our work will be closer to part 1 of assignment 1.3 (describing real world things, like movies), but we wanted you to do parts 2 and 3 to get you to think explicitly about those concepts.

Week 2 focusses on queries. We add variables and logical operators to our language and show how to use them in writing queries, and we give a formal semantics for queries written within this language. As we shall see, the semantics is simple and very precise. However, it is not very practical from a computational point of view. In Week 3, we will look at some practical algorithms for computing answers, and we will suggest some techniques for optimizing queries that takes advantage of these algorithms.

A reminder that we would like you all to form teams and start working with your teammates - on both the biweekly assignments and on the term project. Also, please take advantage of Piazza. If you are confused about something, you might be able to get insight from others. If you have mastered the material, you might be able to help others; and explaining things might help you to understand the material more deeply.

Week 1

Okay. We are on our way! The course begins now. On Tuesday, we will have an introductory presentation on the subject matter of the course and course logistics. On Thursday, we will have our first substantive class.

Your goal this week is to read through and understand the first two chapters of the textbook. The first chapter is just an overview, and it is an easy read. That said, you should not shortchange the material. The chapter talks about the main ideas of Logic Programming and how they relate to each other. The second chapter introduces Datasets. Datasets are fundamental to the theory of Logic Programming, and they are important in practical implementation. The concept is simple, but there are some nuances; and we recommend you read the notes carefully and do the exercises.

You should also drop by Piazza to check out what others in the class are saying. There are some subtleties in Logic Programming that you can miss and that can lead to confusion. Engaging in discussion on the Piazza forum is a good way to deal with these subtleties. And, even if you think you understand everything, you might consider using Piazza to help others and thus consolidate your understanding of the issues.

Note that this week's assignments are due by midnight Sunday night. After this, the assignments for each unit will be due every other week. The "Project" is not due this week. But you should start thinking about what you might want to do. Look at the assignments from last year. And read the suggestions that George will post occasionally on Piazza. We are particularly interested in seeing one or more teams working on program sheets.


Welcome to CS 151. We had hoped this would be a traditional classroom-based course, as in the past. However, due to the continuing Coronavirus situation, that is not an option; and so, once again, we are going to run the course entirely online. We ask for your patience as we proceed. If you think there is a way we could make the course more successful in this format, please feel free to make suggestions.

We will be using Piazza for class discussion. The system is highly catered to getting you help fast and efficiently from classmates and instructors. Rather than emailing questions to the teaching staff, we encourage you to post your questions on Piazza. Just click the rightmost tab above to go to Piazza. (Note that you may need to sign up in order to access the course page on Piazza.) If you have any problems or feedback for the developers, email

Throughout the quarter, we will be using Zoom for live presentations and discussions. To get details, go to Piazza and look for the Zoom link in a pinned post. All sessions will be recorded, and we will place links to the recording in this pinned post as well. Class meetings will take place Tuesdays and Thursdays from 2:30 pm - 3:50 pm PDT. The first session is scheduled for March 30.

Even though this is an online course, we would like to preserve the tradition of working in teams. Ideal size 3, but teams of size 2 or 4 are okay if there are good reasons. (Piazza provides a mechanism for you to find teammates. See the first announcement there to take advantage of this.) Note that, except in extreme circumstances, all team members will receive the same grade. Grades for the course will be based on five assignments and a term project. Each of the assignments will count for 10% of your grade, and the term project will count for 50% of your grade.

Course Description

Logic Programming is a style of programming based on Symbolic Logic. In recent years, there has been increasing interest in Logic Programming due to applications in deductive databases, automated worksheets, Enterprise Management (business rules), Computational Law, and General Game Playing.

This course is an introduction to Logic Programming theory, current technology, and popular applications. Work in the course takes the form of lectures, readings, online exercises, programming assignments, and a term project.

All of the course materials are online here. There are links to notes, background readings, the Sierra logic program development environment, a suite of software tools for analyzing and transforming logic programs, and a Piazza course forum. Click the tabs at the top of this page to access this content. The Lessons tab is your friend. Use it. And be sure to check this page frequently, as we will be posting periodic updates here. If you are desperate for a printed version of the course text, click on the image below to purchase a copy from Amazon.

Note that, as you proceed through the online materials, you may occasionally encounter technical problems. Apologies in advance for this. We are still working on the course. You may get extra credit for reporting such problems (especially if your reports are not overly irate).

Teaching Staff

Mike Genesereth
Vinay Chaudhri
George Younger

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