import java.io.*;
import java.util.*;

public class Database {

  private Map<String,Relation> relations;

  // METHODS

  // Constructor; creates the empty HashMap object
  public Database() {

  }

  // Add relation r with name rname to HashMap
  // if relation does not already exists.
  // Make sure to set the name within r to rname.
  // return true on successful add; false otherwise
  public boolean addRelation(String rname, Relation r) {

  }

  // Delete relation with name rname from HashMap
  // if relation exists. return true on successful delete; false otherwise
  public boolean deleteRelation(String rname) {

  }

  // Return true if relation with name rname exists in HashMap
  // false otherwise
  public boolean relationExists(String rname) {

  }

  // Retrieve and return relation with name rname from HashMap;
  // return null if it does not exist.
  public Relation getRelation (String rname) {

  }

  // Print database schema to screen.
  public void displaySchema() {

  }

}