Problem Set 1

Part I due by 11:59 p.m. on Tuesday, September 16, 2025
Part II due by 11:59 p.m. on Tuesday, September 23, 2025

Preliminaries

If you haven’t already done so, you should complete Lab 0 before beginning this assignment.

In your work on this assignment, make sure to abide by the collaboration policies of the course.

If you have questions, please come to office hours, post them on Piazza, or email cs460-staff@cs.bu.edu.

Make sure to submit your work on Gradescope, following the procedures found at the end of Part I and Part II.

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Part I

30 points total

Creating the necessary folder

1. If you haven’t already created a folder named cs460 for your work in this course, follow these instructions to do so.

2. Then create a subfolder called ps1 within your cs460 folder, and put all of the files for this assignment in that folder.

Creating the necessary file

The problems from Part I will all be completed in a single PDF file. To create it, you should do the following:

1. Access the template that we have created by clicking on this link and signing into your Google account as needed.

2. When asked, click on the Make a copy button, which will save a copy of the template file to your Google Drive.

3. Select File->Rename, and change the name of the file to ps1_partI.

4. Add your work for the problems from Part I to this file.

5. Once you have completed all of these problems, choose File->Download->PDF document, and save the PDF file in your ps1 folder. The resulting PDF file (ps1_partI.pdf) is the one that you will submit. See the submission guidelines at the end of Part I.

Problem 1: ER diagram basics

10 points total

Before going any further, make sure to follow the instructions above to create your own copy of the Google Drive document that you should use for Part I of the assignment.

The ER diagram shown below is part of the design of a database that includes information about actors and the parts that they perform in plays, musicals, movies and TV shows. Each actor has a name and a unique id. Each part can be uniquely identified by the combination of the id of the corresponding show and the name of the role, and the database also keeps track of how many lines of dialogue that each part has (the attribute called line count).

In the above version of the ER diagram, there are no constraints on the relationships between actors and parts.

In the ps1_partI template that we’ve provided on Google Drive (see above), we’ve included the beginnings of three separate versions of this ER diagram.

1. (2 points) Edit the first version of the diagram, adding the connections needed to create an ER diagram whose only constraint is that every part is performed by at least one (i.e., 1 or more) actor. To do so, you should:

   • Click on the diagam and then click the Edit link that appears below the diagram.

   • From the collection of eight connectors that we have provided below the diagram, select the appropriate connectors and use them to connect the two entity sets to the relationship set. Adjust the connectors as needed to make the connections.

   • Click the Save & Close button.

2. (2 points) Edit the second version of the diagram, adding the connections needed to create an ER diagram whose only constraint is that every actor performs at most one (i.e., 0 or 1) part.

3. (2 points) Edit the third version of the diagram, adding the connections needed to create an ER diagram whose only constraints are (1) that every actor performs at least one part, and (2) that every part is played by exactly one actor.

4. (4 points) Consider your answer to part 3—the ER diagram for the situation in which (1) every actor performs at least one part, and (2) every part is played by exactly one actor.

   Is it possible to convert that diagram into a relational schema that has only two tables/relations, or would three be needed? Explain your answer briefly, and then specify the schema of the two or three tables.

   • Give the schema of each table in the form relation_name(attr_name1, attr_name2, ...).

   • Indicate the primary-key attribute(s) of each relation by underlining them.

Problem 2: Database design

12 points total

The ER diagram shown below in Figure 2-1 represents information that is to be stored in a bank database.

Figure 2-1:

Customers borrow loans and own accounts, and accounts have account types.

1. (2 points) At least one of the relationship sets captures a many-to-one relationship. Which one(s)? In your answer, you should specify the direction of each such relationship (e.g., ________ is many-to-one from _________ to ___________).

2. (4 points) Fill in the table that we have provided to describe, for each relationship set in the diagram, any constraints on the relationships associated with that relationship set. Use words that describe the problem domain (e.g., Each course meets in at most one room...) rather than technical terminology.

3. (6 points) Transform this diagram into a relational schema by following the procedure discussed in lecture and fill in the table that we have provided. Here are some additional guidelines:

   • When appropriate, you should combine relations as discussed in lecture. Note: You should assume that most customers do not borrow any loans.

   • In the first column of the table, give the schema of each relation in the form relation_name(attr_name1, attr_name2, ...). Feel free to rename attributes as needed to make them easier to understand. However, if you do so, make sure that you do not use a period or space in an attribute name. Rather, you should use a combination of letters and underscore (_) characters.

   • Indicate the primary-key attribute(s) of each relation by underlining them.

   • If a relation has one or more foreign-key attributes, specify them in the second column of the table, and specify which attribute each foreign key refers to. For example, if you were working with the MajorsIn relation from the university database covered in lecture, its foreign keys would be specified as follows:

     • student, which refers to Student.id
     • department, which refers to Department.name

Problem 3: Combining relations using relational algebra

8 points total; 2 pts. each part

We will finish the material needed for this problem in lecture on Wednesday, September 9.

Relation R has attributes a, b and c. Relation S has attributes d, b, and a. You are given the following instances of these relations:

Relation R

a	b	c
1	2	3
3	4	6
5	6	1

Relation S

d	b	a
3	2	1
5	4	3
9	8	5

For each of the following questions, use the Insert->Table menu option in Google Drive to insert an appropriately sized table for the answer, and then fill in the cells of the table with the correct values.

Make sure that each table includes a header row with appropriate column names.

1. What is the Cartesian product of R and S?
2. What is the natural join of R and S?
3. What is the left outer join of R and S?
4. What is the right outer join of R and S?

Submitting your work for Part I

1. Once you have completed Part I in Google Drive, choose File->Download->PDF document, and save the resulting file (ps1_partI.pdf) in your ps1 folder.

2. Login to Gradescope by clicking the link in the left-hand navigation bar. When logging in, make sure that you use the School Credentials option and select Boston University.

3. Once you are in logged in, click on the box for CS 460. (If you don’t see that box, email cs460-staff@bu.edu ASAP and ask to be added to the course on Gradescope. If the deadline is fast approaching and you don’t have access to CS 460 on Gradescope, email your PDF to cs460-staff@cs.bu.edu before the deadline.)

4. Click on the name PS 1: Part I in the list of assignments. You should see a pop-up window labeled Submit Assignment. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

5. Choose the Submit PDF option, and then click the Select PDF button and find the ps1_partI.pdf that you created in step 1. Then click the Upload PDF button.

6. You should see a question outline along with thumbnails of the pages from your uploaded PDF. For each question in the outline:

   • Click the title of the question.
   • Click the page(s) on which your work for that question can be found.

   As you do so, click on the magnifying glass icon for each page and doublecheck that the pages that you see contain the work that you want us to grade.

7. Once you have assigned pages to all of the problems in the question outline, click the Submit button in the lower-right corner of the window. You should see a box saying that your submission was successful.

8. You can use the Resubmit button at the bottom of the page to resubmit your work as many times as needed before the final deadline.

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Part II

70 points total

Our movie database

The problem domain for this part of the assignment is movie trivia.

Before you get started, you should carefully read over the full description of the database. Please do so now!

Downloading the software and database

1. Go to sqlitebrowser.org/dl.

2. Find the appropriate download link for your machine/operating system, and download and install that version of DB Browser for SQLite.

   • If you have a Mac, you should download the appropriate Mac .dmg file. Double-click on the file, which will open up a window. Then drag the application’s icon to your Applications folder.

   • If you have a Windows machine, you should download the Standard installer for 64-bit Windows (which is an .msi file). Double-click on the file to run the installer. You should be able to use all of the default options.

   • If you are unable to install DB Browser on your own machine, you can use it on the virtual desktop.

3. Download the following files into your ps1 folder:

   • movie.sqlite
   • ps1_queries.py

   If your browser doesn’t allow you to specify where the file should be saved, try right-clicking on the link above and choosing Save as... or Save link as..., which should produce a dialog box that allows you to choose the correct folder for the file.

Using DB Browser for SQLite

1. Launch the program.

2. Click the Open Database button, and find and open the movie.sqlite database file that you downloaded above.

3. To explore the schema of the database, click on the Database Structure tab, and then click on the arrows to the left of the table names.

4. To explore the contents of the tables, click on the Browse Data tab, and then choose the appropriate table from the drop-down menu.

5. Use the Execute SQL tab to perform queries on the database. Enter your SQL command in the space provided, and press F5 or Ctrl-R to run it. (There is also a small button that you can click; it has a triangular shape that looks like the Play button of a music player.)

Important guidelines

1. ps1_queries.py is a Python file, so you could use a Python IDE to edit it, but a regular text editor like TextEdit or Notepad++ would also be fine. However, if you use a text editor, you must ensure that you save it as a plain-text file.

2. Construct the SQL commands needed to solve the problems given below. Test each SQL command in DB Browser for SQLite to make sure that it works.

3. Once you have finalized the SQL command for a given problem, copy the command into your ps1_queries.py file, putting it between the triple quotes provided for that problem’s variable. We have included a sample query to show you what the format of your answers should look like.

4. Unless otherwise stated, each of the problems must be solved by means of a single query (i.e., each query should have a single semi-colon). Use nested subqueries in the WHERE clause as needed. However, you should NOT use nested subqueries in the SELECT clause or FROM clause.

5. You must limit yourself to aspects of SQL that we have discussed in lecture, unless the problem indicates otherwise. At a minimum, failure to do so will result in a score of 0 for the corresponding problem. See our course policies for more detail.

6. Your queries should not use a LIMIT clause.

7. Your queries should only use the keyword DISTINCT if it is necessary to obtain the correct results. Similarly, you should only use an outer join when it is strictly necessary.

8. Make sure that the results produced by your queries contain exact answers to the problems. We should not have to infer the answer from the results. For example, if we ask you how many movies meet a given criterion, we want a number, not a list of the movies. In addition, your results should not include any extraneous information.

Problem 4: The animated Lilo & Stitch

5 points

A non-animated version of Lilo & Stitch was released this year and did very well at the box office. There is also a previous version of the movie with the same name as the one released this year, but that earlier version used animation. All animated movies in the database have the letter N somewhere in the string of letters that make up the value of their genre attribute. For example, The Incredibles has a genre value of 'AVNCFS', with the N indicating that it is animated.

Find the year and runtime of the previous version of Lilo & Stitch by writing a query that makes use of only the following two facts: (1) that the movie’s name is Lilo & Stitch, and (2) that there is an 'N' somewhere in the value of its genre attribute. Use pattern-matching with an appropriate pattern. The result of your query should be a single tuple of the form (year, runtime).

Problem 5: Recent Oscar winners from New York City

5 points

Three of the people who won an Oscar in 2025 were born in New York City. Write a query to find the names of these people and the types of Oscar that they won.

Your query should employ pattern-matching with an appropriate pattern to ensure that you only obtain people whose place of birth begins with the two words “New York”. The result of your query should be tuples of the form (person name, oscar type).

Problem 6: The voice of Stitch

5 points

There is only one person in our database who acted in both of the Lilo & Stitch movies: the actor who provides the voice of the extraterrestrial creature Stitch.

Find the name and dob of this actor by writing a query that makes use of only the fact that he acted in two different movies that were both called “Lilo & Stitch”. You may not make use of any other information that you may know about this actor or about the two movies. The result of the query should be a single tuple of the form (person name, dob).

Hint: One way to solve this problem is to have your FROM clause include multiple instances of at least one of the tables in the database. Remember that in order to do so, you will need to use aliases to distinguish between two instances of the same table.

Problem 7: Counting Oscar-winning comedies

5 points

Write a query to find the number of comedy movies that have won one or more of the Oscars in the database. You should assume that all comedies have the letter 'C' somewhere in their genre string. The result of your query should be a single number.

Problem 8: Oscar winner with the longest runtime

5 points

Write a query to find the name and runtime of the longest movie in the database that has won one or more of the Oscars in the database. If multiple Oscar winners are tied for the longest runtime, you should include all of them. The result of your query should be one or more tuples of the form (movie name, runtime).

Problem 9: Movies with multiple directors

5 points

Most of the movies in the database have only one director. Write a query to find all movies that have more than one. The results of your query should be tuples of the form (movie name, movie year, number of directors). Sort the results in descending order by the number of directors. If multiple movies have the same number of directors, sort them in ascending order by name.

Notes:

• You should assume that the combination of a movie’s name and year is unique.

• When creating subgroups, you are allowed to use more than one attribute as the basis of the subgroups.

Problem 10: No direction for a decade

5 points

Write a query to determine the number of directors in the database who have not directed any of the movies in the database from the last 10 years (i.e., 2015 or later). The result of the query should be a single number.

Problem 11: Oscars for people born in 1960

5 points

This year is the 65th birthday of people who were born in 1960. Write a query that summarizes, for each person in the database who was born in 1960, the number of Oscars in the database (if any) that have been won by that person. The result of the query should be tuples of the form (person name, number of Oscars). If a relevant person has won no awards, they should still appear in the table with a value of 0 for the number of Oscars.

Notes:

• You may assume that no two people born in 1960 have the same name, and that all pob values begin with the year in which the person was born.

• If a person has won two Oscars of the same type (e.g., two Best Director Oscars), each of those Oscars should contribute to the count for that person.

Problem 12: Oscar summary stats

5 points

Write a query that determines, for each type of Oscar included in the database, the following values: the average runtime of all movies associated with that Oscar type, and the number of top-grossing movies associated with that Oscar type. The result of the query should be six tuples of the form (oscar type, average runtime, number of top grossers).

Hint: You should take advantage of the fact that all top-grossing movies have a numeric earnings_rank value, whereas movies that are not top-grossing have an earnings_rank value of NULL.

Problem 13: Shortest and longest

5 points

Write a single query to find both the shortest and longest movies in the database. If multiple movies are tied for being either shortest or longest, they should all be included. The result of the query should be tuples of the form (name, runtime).

Problem 14: Info. about common POBs

5 points

Write a query to find, for all places of birth associated with 10 or more people in the database, the number of people in the database who were born there, and the date of birth of the youngest person in the database who was born there. You should exclude pob values of NULL. The result of the query should be tuples of the form (pob, number of people born there, dob of youngest person born there).

Problem 15: Adding a director’s dob

5 points

Yorgos Lanthimos is a Greek director who has been nominated for five Oscars. The database includes the fact that he was born in Athens, but it is missing his date of birth.

Write a SQL command that adds his date of birth ('1973-09-23') to the database. You may assume that he is the only person in the database named Yorgos Lanthimos.

Hint: This is the only question in which your answer will not be a SELECT command. You will need to figure out the correct type of SQL command to use.

Problem 16: Relational-algebra queries

10 points total; pair-optional

This is the only problem of the assignment that you may complete with a partner. See the rules for working with a partner on pair-optional problems for details about how this type of collaboration must be structured.

Getting started
Your work on this problem should go in a separate PDF file called ps1_problem16.pdf. To create it, you should:

1. Access the template that we have created by clicking on this link and signing into your Google account as needed.

2. When asked, click on the Make a copy button, which will save a copy of the template file to your Google Drive.

3. Select File->Rename, and change the name of the file to ps1_problem16.

4. Add your work for this problem to this file.

5. When you are finished, choose File->Download->PDF document, and save the PDF file on your machine. The resulting PDF file (ps1_problem16.pdf) should be submitted following the instructions below.

The problems
Write a relational-algebra query for each of the following problems. Above, you will write a SQL query for these problems; here you should solve them using relational algebra instead.

See below for some additional guidelines.

1. (3 points) problem 7 (Oscar-winning comedies), but instead of producing a count, your query should produce the names and years of the movies. For the purposes of this problem, you may assume that the combination of a movie’s name and year is unique and that relational algebra includes the same pattern-matching operators as SQL.

2. (3 points) problem 10 (no direction for a decade), but instead of producing a count, your query should produce the ids of the directors. Hint: Take advantage of the set difference operator (-).

3. (4 points) problem 11 (Oscars for people born in 1960), but instead of producing per-person counts, your query should produce tuples of the form (person name, award type, award year). If a given person won multiple awards, there should be one tuple for each of their awards; if they did not win any of the awards in the database, they should have a single tuple in which the second and third values are NULL.

Additional guidelines

• To form your queries, you should use the templates that we have provided for each of the relational-algebra operators at the top of ps1_problem16. Copy the appropriate template(s), and replace the placeholders with the appropriate expressions, attributes and/or predicates to form each query. We have provided an example in ps1_queries of using two of the templates to form a single query.

• For a given problem, you are allowed to perform a sequence of two or more queries in which the results of a given query are assigned to a variable using the assignment operator (<–), and then that variable is used in a subsequent query. We have provided an example of this in ps1_queries, and we recommend that you do this whenever a given query would otherwise become too long or difficult to read.

  Note that using a sequence of queries is not allowed in your SQL answers, but it is allowed here.

Submitting your work for Part II

You will make submissions to two separate assignments on Gradescope. The steps needed for the two submissions are different, so please make sure to follow carefully the procedures outlined below.

PS 1: Problems 4-15
Submit your ps1_queries.py file using these steps:

1. Click on the name of the assignment in the list of assignments. You should see a pop-up window with a box labeled DRAG & DROP. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

2. Add your file to the box labeled DRAG & DROP. You can either drag and drop the file from its folder into the box, or you can click on the box itself and browse for the file.

3. Click the Upload button.

4. You should see a box saying that your submission was successful. Click the (x) button to close that box.

5. The Autograder will perform some tests on your file. Once it is done, check the results to ensure that the tests were passed. If one or more of the tests did not pass, the name of that test will be in red, and there should be a message describing the failure. Based on those messages, make any necessary changes. Feel free to ask a staff member for help.

   Notes:

   • You will not see a complete Autograder score when you submit. That is because additional tests for at least some of the problems will be run later, after the final deadline for the submission has passed. For such problems, it is important to realize that passing all of the initial tests does not necessarily mean that you will ultimately get full credit on the problem. You should always run your own tests to convince yourself that the logic of your solutions is correct.

   • If you get a message saying that the Autograder failed to execute correctly, it is likely the case that one of your queries is taking too long to execute. Make sure that you have checked each query in DB Browser to ensure that it executes correctly, and that you have copied the correct query into your ps1_queries.py file. If you have a query that is causing DB Browser to hang, you should either remove that query from your file before submitting it, or you should comment it out by putting a # symbol at the beginning of each of line of the query.

6. If needed, use the Resubmit button at the bottom of the page to resubmit your work.

7. Near the top of the page, click on the box labeled Code. Then click on the name of your file to view its contents. Check to make sure that it contains the queries that you want us to grade.

PS 1: Problem 16

IMPORTANT: If you chose to work on problem 16 with a partner, only one person from the pair should submit the file, and that person should add the other person as a group member following step 6 below.

Submit your ps1_problem16.pdf file using these steps:

1. If you still need to create a PDF file, open your file on Google Drive, choose File->Download->PDF document, and save the PDF file in your ps1 folder.

2. Click on the name of the assignment in the list of assignments on Gradescope. You should see a pop-up window labeled Submit Assignment. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

3. Choose the Submit PDF option, and then click the Select PDF button and find the PDF file that you created. Then click the Upload PDF button.

4. You should see a question outline along with thumbnails of the pages from your uploaded PDF. For each question in the outline:

   • Click the title of the question.
   • Click the page(s) on which your work for that question can be found.

   As you do so, click on the magnifying glass icon for each page and doublecheck that the pages that you see contain the work that you want us to grade.

5. Once you have assigned pages to all of the questions in the question outline, click the Submit button in the lower-right corner of the window. You should see a box saying that your submission was successful.

6. If you worked with a partner and you are the one who is submitting the file:

   • Click on the Group Members link that appears at the bottom of the page.

   • In the pop-up box that appears, click on the Add Student drop-down menu.

   • Type your partner’s name or choose it from the drop-down menu.

   • Click the Add button.

   • Check to ensure that your partner’s name now appears along with your name under the Group heading in the upper-right corner of the page.

Last updated on September 17, 2025.

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