Java代写 | csc343 Assignment 2

本次Java代写是设计并实现一个航空商务系统
csc343, Winter 2020
Assignment 2
Due: Friday, March 6, before 4pm
In this section, you will write SQL statements to perform queries.
To ensure that your query results match the form expected by the autotester (attribute types and order, for
instance), we are providing a schema template for the result of each query. These can be found in files q1.sql,
q2.sql, . . . , q5.sql. You must add your solution code for each query to the corresponding file. Make sure that
each file is entirely self-contained, and does not depend on any other files; each will be run separately on a fresh
database instance, and so (for example) any views you create in q1.sql will not be accessible in q5.sql.
1
The queries
These queries are complex, and we have tried to specify them precisely. Generally speaking, if behaviour is not
specified in a particular case, we will not test that case.
Design your queries with the following in mind:
• When we say that a passenger took a flight, we mean that the flight was completed, that is, it has gone from
departure to arrival. You can assume that if a departure was made, an arrival also occured.
• Each flight has scheduled departure and arrival times, which are the times presented to the passenger upon
booking a flight. The actual departure and arrival times arrivals are specified in the Departure and Arrival
tables.
• The date that a passenger took the flight is the date of the actual departure (not the scheduled departure
time).
• All timestamps are in one time zone (UTC).
Write SQL queries for each of the following:
1. Airlines. For each passenger, report their passenger ID, full name, and the number of different airlines on
which they took a flight.
Attribute
pass id id of a passenger.
name full name of the passenger (for example, Kelly Watts).
airlines the number of different airlines on which they took a flight.
Everyone? Every passenger should be included, even if they have never taken a flight.
Duplicates? No passenger can be included more than once.
2. Refunds! Airlines offer refunds for late departures as follows:
For domestic flights (flights within the same country), a 35% refund is given for a departure delay of 4 hours
or more, and a 50% refund for 10 hours or more.
For international flights (flights between different countries), a 35% refund is given for a departure delay of 7
hours or more, and a 50% refund for 12 hours or more.
However, if the pilots manage to make up time during the flight and have an arrival delay that is at most half
of the departure delay, then no refund is provided, regardless of how many hours the delay was.
For every airline and year that the airline had flights which required refunds, return the total refund money
given in that particular year in each seat class. This means there should be at most three records per airlineyear
combination (you should not include a seat class if no one booked it for any refunded flight). The year
of a flight comes from its scheduled departure date.
Attribute
airline the airline code.
name the airline name.
year a specific year.
seat class one of the three seat classes (economy, business, first).
refund the total money refunded to that seat class that year.
Everyone? Every airline-year-seat class combination should be included in each year the airline had a flight
which required refunds, unless a seat class had no bookings that year for a refunded flight, then you
should not include that seat class.
Duplicates? No duplicates.
2
3. North and South Connections. Business passengers that travel between the US and Canada sometimes
want to get to their destination on the same day they left, and as early as possible. Because of limited
same-day flight options, they may also have to connect through one or two different airports before reaching
their destination.
Consider the day April 30, 2020 (2020-04-30). For each pair of outbound/inbound cities (not airports – a city
can have multiple airports) between Canada and the USA (in both directions, list the number of possible
different routes that a passenger can take on that day to get from the outbound city to the inbound city. You
should list the numbers in three different columns: one for the number of direct flight routes (no connections),
one for the number of one-connection routes, and one for the number of two-connection routes. In addition,
you should include the earliest possible arrival time to the inbound city from all of the routes you found.
Note: A minimum connection time of 30 minutes is required so passengers have a chance to get from one
plane to the next.
Attribute
outbound the outbound city.
inbound the inbound city.
direct the total number of possible direct routes that start and end on April 30, 2020.
one con the total number of possible one-connection routes that start and end on April 30, 2020.
two con the total number of possible two-connection routes that start and end on April 30, 2020.
earliest the earliest possible arrival time (full timestamp) from all of
the direct, one-connection, and two-connection routes.
Everyone? Include all pairs of cities between Canada and the USA in both directions
(e.g. Toronto to New York and New York to Toronto).
Duplicates? No duplicate outbound/inbound city pairs.
4. Plane capacity histogram. Create a table that is, essentially, a histogram of the percentages of how full
planes have been on the flights that they have made (that is, only the flights that have actually departed).
The upper bounds in the ranges below are non-inclusive.
Attribute
airline the airline of the plane.
tail number the tail number of the plane.
very low The number of flights that the plane had between 0% and 20% capacity.
low The number of flights that the plane had between 20% and 40% capacity.
fair The number of flights that the plane had between 40% and 60% capacity.
normal The number of flights that the plane had between 60% and 80% capacity.
high The number of flights that the plane had more than 80% capacity.
Everyone? Every plane should be included, even if they haven’t flown at all.
Duplicates? No plane can be included more than once.
3
5. Flight hopping. For this query, you are going to learn about and use two interesting features of PostgreSQL:
Common Table Expressions and the RECURSIVE clause.
A Common Table Expression (CTE) is very similar to a VIEW, except instead of saving the view in your
schema, you simply use the expression immediately.
You can define a CTE using the WITH clause, and then use it immediately, all within one query execution:
WITH air_canada_flights AS — air_canada_flights is the CTE
(SELECT * FROM Flight f
WHERE f.airline = ‘AC’ )
SELECT * from air_canada_flights;
Notice how the semicolon is at the end of the entire query, showing that the CTE declaration (WITH) and the
subsequent SELECT statement all happen together, as opposed to separately as in the case of a VIEW.
The RECURSIVE clause allows you to start with a base CTE, and use it to write recursive queries. For example,
the query below counts the numbers from 1 to 10:
WITH RECURSIVE numbers AS (
(SELECT 1 AS n) — the ’base’ query
UNION ALL
(SELECT n + 1 FROM numbers WHERE n < 10) — the recursive query
)
SELECT * FROM numbers;
The base query starts the count by setting the numbers CTE to have only the number 1. Then that CTE is fed
into the recursive query, and a table with only the number 2 is produced and assigned to numbers. Then that
table is fed into the recursive query and we get 3, and so on until the terminating condition, WHERE n < 10,
stops the execution of the recursive queries. We then do a UNION ALL to include all the records from every
execution of the recursive query.
You can read more about the RECURSIVE clause here and find examples on how to use it:
https://www.postgresqltutorial.com/postgresql-recursive-query/
“Flight hopping” is defined as getting on a plane, landing at a destination, and then within 24 hours getting
on another plane from that destination. You can keep doing this, hopping from flight to flight, as long as the
time interval between the arrival of one flight and the departure of the next one is less than 24 hours.
Suppose we start at Toronto’s Pearson Airport (YYZ). For a given date and maximum number of flights, list
all possible airports you can get to on every number of flights up to the maximum by flight hopping, and the
number of flights it takes to get to that destination. Keep all airports, even if you could get to them by a
different number of flights (up to the max).
Use only scheduled departure and arrival times. We will not enforce a minimum connection time like query 3.
Attribute
destination an airport code for the final destination of a flight-hopping session.
num flights the number of flights it took to get to that airport through 24-hour flight hopping.
Everyone? Include all airport destinations you can flight hop to (including the origin airport, YYZ, which
would require at least two flights). Include only those from the given start date
and all number of flights up to the maximum.
The date and maximum number of flights will be provided from
the q5_parameters relation.
Duplicates? Duplicates should be included if there are multiple routes that can get you to
the same destination in the same number of flights.
SQL Tips
• There are many details of the SQL library functions that we are not covering. It’s just too vast! Expect
to use the postgreSQL documentation to find the things you need. Chapter 9 on functions and operators
4
is particularly useful. Google search is great too, but the best answers tend to come from the postgreSQL
documentation.
• When subtracting timestamp values, you get a value of type INTERVAL. If you want to compare to a constant
time interval, you can do this, for example:
WHERE (a – b) > INTERVAL ’0’
Or, you can write an explicit time interval:
WHERE (a – b) > ‘01:30:00’ — greater than 1 hour and 30 minutes.
• Please use line breaks so that your queries do not exceed an 80-character line length.
Continued on next page…
5
Part 2: Embedded SQL
Imagine an integrated system for an airline that allows passengers and airline workers to perform tasks. This could
be something like booking flights for passengers, or seeing an overview of the plane’s current seating arrangements
for the check-in counter at the airport. The app could have a graphical user-interface, written in Java, but ultimately
it has to connect to the database where the core data is stored. Some of the features will be implemented by Java
methods that are merely a wrapper around a SQL query, allowing input to come from gestures the user makes on
the app, like button clicks, and output to go to the screen via the graphical user-interface. Other app features will
include computation that can’t be done, or can’t be done conveniently, in SQL.
For Part 2 of this assignment, you will not build a user-interface, but will write several methods that the app would
need. It would need many more, but we’ll restrict ourselves to just enough to give you practise with JDBC.
General requirements
• You may not use standard input in the methods that you are completing. Doing so will result in the autotester
timing out, causing you to receive a zero on that method. (You can use standard input in any testing code
that you write outside of these methods, however.)
• You may not change the header of any of the methods we’ve asked you to implement, not even to declare
that a method may throw an exception. Each method must have a try-catch clause so that it cannot possibly
throw an exception.
• You will be writing a method called connectDb() to connect to the database. When it calls the getConnection()
method, it must use the database URL, username, and password that were passed as parameters to connectDb();
these values must not be “hard-coded” in the method. Our autotester will use the connectDb() and
disconnectDB() methods to connect to the database with our own credentials.
• You should not call connectDb() and disconnectDB() in the other methods we ask you to implement; you
can assume that they will be called before and after, respectively, any other method calls.
• All of your code must be written in Assignment2.java. This is the only file you may submit for this part.
• You are welcome to write helper methods to maintain good code quality.
• Carefully read the section on the next page entitled ‘How seats are booked’ to understand the appropriate
way to write your methods.
Your task
Complete the following methods in the starter code in Assignment2.java:
1. connectDB: Connect to a database with the supplied credentials.
2. disconnectDB: Disconnect from the database.
3. bookSeat: A method that would be called when a passenger wants to book a seat on a plane.
4. upgrade: A method that would be called to see if economy class passengers without a seat can be upgraded
to business or first class when economy class is overbooked (more economy bookings than economy seats).
You should not call upgrade from bookseat or vice-versa.
6
How seats are booked
Seats are assigned automatically by the system when a passenger books a flight. To keep things consistent, we will
constrain this process like so:
• In every plane, there are 6 seats per row, designated by the letters A,B,C,D,E, and F.
For example, the seat 1E represents the fifth seat in row 1.
• There are three seat classes, first class, which starts at row 1, followed by business class, and then economy.
• When a passenger wants to book a seat in a particular seat class, seats are assigned row by row, from A to F
across the row, until the capacity of a seat class is reached. At that point, a new row starts for the next seat
class.
For example, if there are 8 seats in first class, the seats are booked in this order: 1A, 1B, 1C, 1D, 1E, 1F, 2A, 2B.
For the next class, business class, we start on a new row, so the first seat to be booked will be 3A. If there are
15 seats in business class, the last seat in business class will be 5C, and the first seat in economy will be 6A.
• Economy class can be overbooked. Up to 10 seats after filling up all economy seats, passengers will not get
a seat booked, and instead will have NULL values for the seat number and letter. After 10 NULL seats are
booked, no more can be booked.
After bookings are done, airline workers can attempt to upgrade NULL seats from economy to a higher seat
class, starting with business, followed by first class (with seats assigned in the same order as normal booking).
Upgrades are done in order of earliest booking. If there are no seats remaining in the higher classes to upgrade
the overbooked seats, then those passengers will unfortunately not be able to take the flight.
You should use these constraints and assumptions when writing your code.
Read the Javadoc in the code for more information on what you must do.
SQL vs. Java
You will have to decide how much to do in SQL and how much to do in Java. At one extreme, you could use the
database for very little other than storage: for each table, you could write a simple query to dump its contents into
a data structure in Java and then do all the real work in Java. This is a bad idea. The DBMS was designed to
be extremely good at operating on tables! You should use SQL to do as much as it can do for you. In particular,
there is no need to use a Java data structure such as an ArrayList, HashMap, or Set, or even a simple array.
We don’t want you to spend a lot of time learning Java for this assignment, so feel free to ask lots of Java-specific
questions as they come up.
Additional JDBC tips
Some of your SQL queries may be very long strings. You should write them on multiple lines for readability, and
to keep your code within an 80-character line length. But you can’t split a Java string over multiple lines. You’ll
need to break the string into pieces and use + to concatenate them together. Don’t forget to put a blank at the end
of each piece so that when they are concatenated you will have valid SQL. Example:
String sqlText =
“select pass_id ” +
“from Passenger r join Booking b on r.pass_id = b.pass_id ” +
“where r.fname = ?”;
Note that seat_class is a user-defined type in the ddl file. For a query string, instead of just putting a question
mark ?, you should put (?::seat_class), indicating the user-defined type.
Then you can set it in the PreparedStatement, for example: ps.setString(1, “economy”);


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