Description
In this homework, you will implement a (very) simple database management system for our custom database
query language. Your program should ask for queries to execute until program termination.
In this section, semantics of the query language (i.e. permanent changes on database and console output) will
be explained. This intuitive explanation is based on examples. For a formal specification of syntax and example
scenarios, see Appendix A and B. Appendix C provides useful snippets and Appendix D explains evaluation
criteria.
Create File
The query below will create a file to store some attributes (namely, “name”, “department” and “email”) of students
and then print one of the given outputs below:
create file students with name,department,email
Output:
Corresponding file was successfully created.
or (if a file with such name already exists)
There was already such a file. It is removed and then created again.
or (if the query contains id as an attribute)
You cannot create a file with attribute ‘id’.
Delete File
The query below will delete the corresponding file and then print one of the outputs given below:
delete file employee_information
Output:
Corresponding file was successfully deleted.
or (if such a file does not exist)
There is no such file.
Display Files
The query below will print such an output:
display files
Output (an example):
Number of files: 2
1) students: id,name,department,email
2) countries: id,name,GDP,continent
Add Line
The query below will add a line to the corresponding file and then print one of the outputs given below:
add Thimo_Adler,CENG,lorem@ipsum.com into students
Output (id may be different):
New line was successfully added to students with id = 1.
or (if there are missing or extra values in query)
Numbers of attributes do not match.
or (if such a file does not exist)
There is no such file.
Note: A special attribute named id is never explicitly mentioned in queries to create files, but it is automatically
added to any file. When a line is added to a file, the corresponding id is not provided by user. Instead, a unique
positive integer should be generated by your code and assigned to that line as id. Please note that ids do not
have to be consecutive, but they have to be unique.
Remove Lines
The query below will remove some lines from the corresponding file and print one of the outputs given below:
remove lines from countries where continent == South_America
Output (number of lines may be greater than or equal to 0):
2 lines were successfully removed.
or (if the attribute in condition does not exist in file)
Your query contains an unknown attribute.
or (if such a file does not exist)
There is no such file.
Modify Lines
The query below will modify some lines in the corresponding file and then print one of the outputs given below:
modify email in students as loremipsum@iyte.edu.tr where email == lorem@ipsum.com
Output (number of lines may be greater than or equal to 0):
0 lines were successfully modified.
or (if user wants to change id value, which is not allowed):
Id values cannot be changed.
or (if an attribute that is mentioned in query does not exist in file)
Your query contains an unknown attribute.
or (if such a file does not exist)
There is no such file.
Fetch Lines
The query below will fetch some lines from the corresponding file and then print one of the outputs given below:
fetch name,id,email from students where id != 2
Output (an example, note that columns are aligned):
Number of lines in file students: 4
Number of lines that hold the condition: 3
————————————————————–
| name | id | email |
————————————————————–
| Lorem_Ipsum | 1 | lorem.ipsum@example.com |
| Dolor_Sit_Amet | 5 | hello@dolorsitamet.info |
| Consectetur_Adipiscing_Elit | 6 | 123456@iyte.edu.tr |
————————————————————–
or (if an attribute that is mentioned in query does not exist in file)
Your query contains an unknown attribute.
or (if such a file does not exist)
There is no such file.
Invalid Queries
If a query does not fit into formal definition of valid queries in Appendix A, then print the output:
Invalid query.
Program Termination
Program will terminate if the user enters x as input.
Persistency
There are 7 query types. Of the 7 query types, only 2 make no change on database (namely, ‘display’ and
‘fetch’). If a query requires to make a change on database, make the change persistent. First, save the changes
into the related file, and then print the information message to the console. This will guarantee that example
scenarios will run the same way even if user restarts your program in the middle of a scenario.
File Format
You can decide your file extension and design content format as you wish as long as it is consistent. A sequence
of arbitrary queries and a final version of corresponding file in an example format are given below. Note that
output is ignored.
create file Players with name,team
add Cristiano_Ronaldo,Real_Madrid into Players
add Lionel_Messi,FC_Barcelona into Players
Players.hw3
id,name,team
1,Cristiano_Ronaldo,Real_Madrid
2,Lionel_Messi,FC_Barcelona
Appendix A: Syntax of Query Language
Specification of our query language in (simplified) Backus-Naur form is shown below. Note that vertical bars are
used to provide alternatives.
Query::= Create | Delete| Display | Add| Remove| Modify| Fetch
Create::= create file Identifierwith Identifiers
Delete::= delete file Identifier
Display::= display files
Add::= add Identifiersinto Identifier
Remove::= remove lines from Identifierwhere IdentifierOperatorIdentifier
Modify::= modify Identifierin Identifieras Identifierwhere IdentifierOperatorIdentifier
Fetch::= fetch Identifiersfrom Identifierwhere IdentifierOperatorIdentifier
Operator::= ==|!=
Identifiers::= One or more Identifier s connected with commas
Identifier::= Any non-empty string that contains only English letters, digits, ‘_’ (underscore), ‘.’ (dot) and ‘@’ (at)
Warning: Please mind space characters around operators. Note that queries are totally case-sensitive (e.g.
“DISPLAY FILES” is invalid and “delete file BOOKS” will not remove “books”). Also note that space character is
not allowed for an identifier (e.g. “add Tales from the Borderlands,2014 into Games” is an invalid query), and
there is no space character between identifiers (e.g. “create file countries with name, GDP” is an invalid query).
Any query that does not fit into definition above should be counted as invalid. A valid query for each type is
shown below:
Query Type Valid Query Example
Create create file employee.information with name,department,salary
Delete delete file CENG_Students
Display display files
Add add Cristiano_Ronaldo,Real_Madrid into Players
Remove remove lines from movies where id != -1
Modify modify type in publications as conference_paper where type == conference
Fetch fetch id,salary from employees where department == software_development
Note: Each condition consists of an attribute name and a value. The attribute name is always at the left-hand
side and the value is at the right-hand side.
Assumption: Special English words that are mentioned in query definitions are keywords (e.g. “create”, “where”,
“in”, etc.). Identifiers may contain keywords (e.g. “Of_Mice_and_Man” that contains “and” and “Geoffrey_Hinton”
that contains “into” are valid identifiers). However, for the sake of simplicity, you can safely assume that no
identifier will be equal to a keyword (e.g. user will not enter “files”, “lines” and “as” as identifiers).
Appendix B: An Example Scenario
What is your query?
create file books with ISBN,title,genre,author,publisher
Corresponding file was successfully created.
What is your query?
create file books with ISBN,title,genre,author,publisher,year
There was already such a file. It is removed and then created again.
What is your query?
fetch id,title,author from books where id == 1
Number of lines in file students: 0
Number of lines that hold the condition: 0
———————–
| id | title | author |
———————–
What is your query?
add 1943138427,Animal_Farm,Dystopian,George_Orwell,Penguin_UK,1946 into books
New line was successfully added to books with id = 1.
What is your query?
add 0679722769,Ulysses,Fiction,James_Joyce,Dover,1922 into books
New line was successfully added to books with id = 2.
What is your query?
add 9780060850524,Brave_New_World,Dystopian,Aldous_Huxley,Harper into books
Numbers of attributes do not match.
What is your query?
fetch id,title,author from books where id == 1
Number of lines in file students: 2
Number of lines that hold the condition: 1
————————————
| id | title | author |
————————————
| 1 | Animal_Farm | George_Orwell |
————————————
What is your query?
create file movies with title,genre,director,minutes,year
Corresponding file was successfully created.
What is your query?
add Yesterday,Help,The_Beatles,Rock,1966 into songs
There is no such file.
What is your query?
add Death_Note,Adventure,Adam_Wingard,101,2017 into movies
New line was successfully added to movies with id = 1.
What is your query?
add My_Neighbor_Totoro,Anime,Hayao_Miyazaki,86,1988 into movies
New line was successfully added to movies with id = 2.
What is your query?
display files
Number of files: 2
1) books: id,ISBN,title,genre,author,publisher
2) movies: id,title,genre,director,minutes,year
What is your query?
create file songs with title,album,artist,genre,year
Corresponding file was successfully created.
What is your query?
display files
Number of files: 3
1) books: id,ISBN,title,genre,author,publisher
2) movies: id,title,genre,director,minutes,year
3) songs: id,title,album,artist,genre,year
What is your query?
add Yesterday,Help,The_Beatles,Rock,1966 into songs
New line was successfully added to songs with id = 1.
What is your query?
add Sea_Of_Monsters,Yellow_Submarine,The_Beatles,Rock,1969 into songs
New line was successfully added to songs with id = 2.
What is your query?
add Time,The_Dark_Side_Of_The_Moon,Pink_Floyd,Rock,1973 into songs
New line was successfully added to songs with id = 3.
What is your query?
remove lines from songs where artist == The_Beatles
2 lines were successfully removed.
What is your query?
remove lines from books where artist == James_Joyce
Your query contains an unknown attribute.
What is your query?
delete file songs
Corresponding file was successfully deleted.
What is your query?
remove lines from songs where artist == Pink_Floyd
There is no such file.
What is your query?
modify album in songs as Greatest_Hits where title == Yesterday
There is no such file.
What is your query?
modify publisher in books as Vintage where titl == Ulysses
Your query contains an unknown attribute.
What is your query?
modify publisher in books as Vintage where title == Ulysses
1 lines were successfully modified.
What is your query?
modify id in movies as 5 where title == Death_Note
Id values cannot be changed.
What is your query?
add 9750718533,Nineteen_Eighty_Four,Dystopian,George_Orwell,Penguin,1949 into books
New line was successfully added to books with id = 3.
What is your query?
fetch id,title from books where author == George_Orwell
Number of lines in file students: 3
Number of lines that hold the condition: 2
—————————–
| id | title |
—————————–
| 1 | Animal_Farm |
| 3 | Nineteen_Eighty_Four |
—————————–
What is your query?
Display files
Invalid query.
What is your query?
x
Appendix C: Some Useful Snippets
The snippet below will retrieve names of files that exist in your working directory. You can later filter them
according to their extensions.
import os
file_names = os.listdir()
The following snippet will delete the mentioned file in your working directory. Furthermore, you should check if
such a file really exists (using os.listdir()) before executing the remove function in order to prevent possible
errors.
import os
file_name = “Mona Lisa.jpg”
os.remove(file_name)
Note:Importing os (operating systems) module for once is necessary and sufficient.
Appendix D: Submission Rules and Evaluation Criteria
Submission Rules
● You should submit your assignments through CMS until due date.
● Your homework should be named as CENG113_hw3_studentID.py (e.g. CENG113_hw3_123456789.py).
● Write your student ID as a comment at the beginning of your code.
Note: Violation of any submission rule may end up with point deduction up to 100 points. Any kind of cheating
including teamwork will be penalized. Your program will be tested on Linux.
Evaluation Criteria
(70 points) Performance on test cases: correctness of console output with respect to functionality and style for
several independent scenarios including given scenario in Appendix B, short scenarios, single-query scenarios,
invalid queries, and program termination between queries.
(15 points) Code readability: meaningful identifiers (names of variables, functions, etc.) with a consistent style,
comments (when, and only when necessary), indentation and consistent use of spaces, separation of main
program and function definitions, etc.
(15 points) Modular programming: control abstraction (functions for subprograms and sub-subprograms when
necessary, relatively short and simple main program, etc.), reusable code, absence of code repetition, etc.
