Csc 1302, Honors Principles of Computer Science II (Fall 2021)

Week 6 (1 October 2021)

Project Operator

During this week you will write the following methods:

1. (Tuple.java):

   // This method takes as input an array list of column names, each of which
   // belonging to this.attributes, and returns a new tuple with only those
   // components that correspond to the column names in cnames.
   public Tuple project(ArrayList<String> cnames) {
     Create an array list, doms, with domains values for column names in cnames
     (Note: you would need .indexOf() method of ArrayList to determine the index where the column name is stored)
     Create a new Tuple object, tup;
     for each column name in cnames:
       add corresponding component of this.tuple to tup;
     return tup;
   }
   

2. (Relation.java) Project Operator:

   // This methods takes as input an array list of column names, each of which
   // belonging to this.attributes, and returns a relation whose tuples are
   // formed by projecting the columns from cnames.
   // Example: R(A:INTEGER, B:INTEGER, C:DECIMAL) with tuples
   // {(10,20,3.5),(11,22,7.8),(10,25,3.5)}
   // Then, with cnames = {A,C}, the output relation should
   // have schema (A:INTEGER, C:DECIMAL) and tuples
   // {(10,3.5),(11,7.8)}
   // Note that after projection one may get duplicate tuples, which should
   // be deleted.
   public Relation project(ArrayList<String> cnames) {
     Create new attrs and doms from cnames and this.domains;
     Create a new Relation object, rel;
     for each tuple in this.table:
       call the project() method of Tuple class and get a new tuple;
       add the new tuple to this.table;
     Remove duplicates from rel;
     return rel;
   }
   

Download the Driver Programs and implement all the methods in this assignment. Compile and run the driver programs. You should see the following output when you run Driver.java:

[raj@tinman w4]$ java Driver
STUDENT(SID:INTEGER,SNAME:VARCHAR,PHONE:INTEGER,MAJOR:VARCHAR,GPA:DECIMAL)
Number of tuples: 4

1111:Robert Adams:1234:Computer Science:4.0:
1112:Charles Bailey:5656:Computer Science:3.5:
1113:David Beatle:1212:Mathematics:3.5:
1114:Graham Gooch:5678:Computer Science:3.5:

PROJECT_SID_GPA_STUDENT(SID:INTEGER,GPA:DECIMAL)
Number of tuples: 4

1111:4.0:
1112:3.5:
1113:3.5:
1114:3.5:

PROJECT_MAJOR_GPA_STUDENT(MAJOR:VARCHAR,GPA:DECIMAL)
Number of tuples: 3

Computer Science:4.0:
Computer Science:3.5:
Mathematics:3.5:

PROJECT_MAJOR_STUDENT(MAJOR:VARCHAR)
Number of tuples: 2

Computer Science:
Mathematics: