COP 4020 — Programming Languages 1 November 25, 2008
Homework 6: Relational Programming
(aka Logic Programming)
Due: Friday, December 5, 2008 at 11pm.
In this homework you will learn a bit about the relational model and basic techniques of logic pro-
gramming. The programming techniques include specification of relationships and using generate and test
[Concepts] [UseModels]. A few problems also make comparisons with the other models we have studied,
and also with embeddings of the relational model in other languages [EvaluateModels] [MapToLanguages].
Your code should be written in the relational model of chapter 9 of our textbook [RH04]. Thus you
should not use cells and assignment in your Oz solutions. Furthermore, note that the relational model does
not include the primitive IsDet or the library function IsFree; thus you are also prohibited from using
either of these functions in your solutions.
You should use helping functions whenever you find that useful. Unless we specifically say how you are
to solve a problem, feel free to use any functions from the Oz library (base environment), especially functions
like Map and FoldR.
For all Oz programing tasks, you must run your code using the Mozart/Oz system. For these you must
also provide evidence that your program is correct (for example, test cases). Oz code with tests for various
problems is available in a zip file, which you can download from the course resources web page. For testing,
you may want to use tests based on our code in the course library file TestingNoStop.oz.
Turn in (on Webcourses) your code and, if necessary, output of your testing for all questions that require
code. Please upload text files with your code that have the suffix .oz and text files with suffix .txt that
contain the output of your testing. Please use the name of the main function as the name of the file. (In any
case, don’t put any spaces in your file names!)
If we provide tests and your code passes all of them, you can just indicate with a comment in the code
that your code passes all the tests. Otherwise it is necessary for you to provide us test code and/or test output.
If the code does not pass some tests, indicate in your code with a comment what tests did not pass, and try
to say why, as this enhances communication and makes commenting on the code easier and more specific to
your problem than just leaving the buggy code without comments.
If you’re not sure how to use our testing code, ask us for help.
Your code should compile with Oz, if it doesn’t you probably should keep working on it. If you don’t
have time, at least tell us that you didn’t get it to compile.
Be sure to clearly label what problem each area of code solves with a comment.
Don’t hesitate to contact the staff if you are stuck at some point.
Read Chapter 9 of the textbook [RH04]. (See the syllabus for optional readings.)
Message Passing Semantics and Expressiveness
1. [Concepts]
(a) (5 points) [EvaluateModels]
Could the relational model be used to implement a data abstraction, Box as in the previous home-
work, which acts like a cell? Briefly explain.
(b) (5 points) [MapToLanguages]
Why is the notion of encapsulated search, using Solve, appropriate for making logic program-
ming features available in a language such as Java? Briefly explain.
(c) (10 points) [Concepts]
Briefly describe (in English) a specific programming problem that is not part of this homework
and is not in the textbook, but for which logic programming would be the most appropriate model.
Also briefly explain why logic programming would be good for your problem.
1
