Homework 2: Translating between the ER and relational models Due at 5pm on Wednesday, April 25

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1 CS 461, Databases Systems, Spring 2018 Description Homework 2: Translating between the ER and relational models Due at 5pm on Wednesday, April 25 This assignment covers translation between the two models we covered in class: entity relationship (ER) and relational. I do not expect you to use any special software to draw ER diagrams. The easiest way is to print out this assignment, draw the diagrams by hand, scan in and submit. Grading This assignment is made up of 3 problems, collectively worth 90 points, or 5% of the over-all course grade. If this assignment is submitted late, you will receive no credit. This assignment is to be completed individually. Please consult the course syllabus for a description of our academic honesty policy. Submission instructions Submit your assignment to gitlab on gitlab.cci.drexel.edu. I assume that you already followed the steps to create your git repository, as outlined in the Resources area of the course website ( I will refer to the root directory of your git repository as $GIT_HOME. Create a directory called cs461-hw2 (case-sensitive, use exactly this name) under $GIT_HOME: mkdir $GIT_HOME/cs461-hw2 cd $GIT_HOME/cs461-hw2 Place the file or file you wish to submit, e.g., hw2.pdf into this directory. You can now commit your assignment as follows: git add * git commit -m homework 2 git push You may submit multiple times before the deadline, only your last submission committed before the deadline will be graded.

2 Part 1 (20 points): ER to relational Consider ER diagrams below. Write one or several create table statements that implement the entity sets, relationship sets and constraints encoded by the diagrams. Give a brief explanation of your implementation, explaining how you encoded the constraints specified by the diagram. If a constraint cannot be encoded you must state so explicitly. (a) (10 points) Assume that id attributes are underlined, and are of type integer. Assume that name attributes are of type char(32). Arrow from A to rel is not bold, arrow from C to rel is bold.

3 (b) (10 points) Assume that id attributes are underlined, and are of type integer. Assume that name attributes are of type char(32). Arrow from A to rel1 is not bold, arrow from C to rel2 is bold.

4 Part 2 (20 points): Relational to ER Consider create table statements below. In each question, draw an ER diagram from which these create table statements could have been derived. Be sure to mark any key and participation constraints. (a) (10points) create table Foo ( X integer primary key, Y integer unique, Z integer not null, foreign key (Y) references Bar(Y) create table Bar ( Y integer primary key create table Baz ( X integer primary key, W integer not null, foreign key (X) references Foo(X)

5 (b) (10points) create table R ( rid integer primary key, name varchar(64) not null create table S ( sid integer primary key, name varchar(64) not null, rid integer not null unique, foreign key (rid) references R(rid) create table T ( tid integer primary key, val float, sid integer, foreign key (sid) references S(sid)

6 Part 3 (50 points): ER to relational, revisited Consider the ER diagrams below. In each question, write create table statements that correctly translate this diagram. Briefly explain how your create table statements implement key and participation constraints. If a constraint cannot be represented in SQL you should state so in your description. (a) (10 points) name% isolympic% name% dob% play& SPORTS& ATHLETES& name% belong_to& TEAMS& The line from ATHLETES to play is bold and has an arrowhead. The line from ATHLETES to belong_to has an arrowhead but is not bold. The line from TEAMS to belong_to is bold.

7 (b) (10 points) The lines from GALLERIES to own, and from GALLERIES to display, are bold. The line from PAINTINGS to own is bold and has an arrowhead.

8 (c) (15 points) The line from AIRLINES to operate is bold. The line from FLIGHTS to operate has an arrowhead. The line from FLIGHTS to connect is bold.

9 (d) (15 points) name Satellites name diameter mass orbital_period Planets orbit period orbit named after name brightness name mythology Stars metallicity Deities The line from PLANETS to orbit is bold and has an arrowhead. The line from PLANETS to named after has an arrowhead. The line from SATELLITES to orbit is bold and has an arrowhead. The frames of SATELLITES and of orbit are bold.