Csc 1302, Honors Principles of Computer Science II (Fall 2023)

Week 4 (17 September 2023)

Pseudo Code for Union, Intersect, and Minus

During class, you will complete coding of the Tuple.clone(), Relation.member(), and the union, intersect, and minus operators. Pseudo code is given for some of these methods:

def union(self,r2):
  ## Schema part of output relation
  Create empty array list for attributes of output relation, call it attrs
  Create empty array list for domains of output relation, call it doms
  Copy values from attributes of "self" relation into attrs
  Copy values from domains of "self" relation into doms
  Create a new Relation object, called rel, with attributes attrs and domains doms, name can be null

  ## Instance part of output relation
  Clone each tuple from the "self" relation and add to rel
  Clone each tuple from r2 and add to rel
  remove duplicates from rel
  return rel

def intersect(self,r2):
  ## Schema part of output relation
  Create empty array list for attributes of output relation, call it attrs
  Create empty array list for domains of output relation, call it doms
  Copy values from attributes of "self" relation into attrs
  Copy values from domains of "self" relation into doms
  Create a new Relation object, called rel, with attributes attrs and domains doms, name can be null

  ## Instance part of output relation
  for each tuple in "self" relation:
    if tuple also belongs to r2 then
      Clone tuple add to rel
  return rel

def minus(self,r2):
  ## Schema part of output relation
  Create empty array list for attributes of output relation, call it attrs
  Create empty array list for domains of output relation, call it doms
  Copy values from attributes of "self" relation into attrs
  Copy values from domains of "self" relation into doms
  Create a new Relation object, called rel, with attributes attrs and domains doms, name can be null

  ## Instance part of output relation
  for each tuple in "self" relation:
    if tuple does not belong to r2 then
      Clone tuple add to rel
  return rel