package simpledb;
import java.util.*;

/**
 * DbIterator is the iterator interface that all SimpleDB operators should
 * implement.
 */
public interface DbIterator {
  /**
   * Opens the iterator.
   * @throws NoSuchElementException when the iterator has no elements.
   * @throws DbException when there are problems opening/accessing the database.
   */
  public void open() 
      throws NoSuchElementException, DbException, TransactionAbortedException;

  /**
   * Gets the next tuple from the operator (typically implementing by reading
   * from a child operator or an access method).
   *
   * @return The next tuple in the iterator.
   * @throws NoSuchElementException if there are no more tuples
   */
    public Tuple getNext() throws TransactionAbortedException, DbException, NoSuchElementException;

  /**
   * Resets the iterator to the start.
   * @throws DbException When rewind is unsupported.
   */
  public void rewind() throws DbException, TransactionAbortedException;

  /**
   * Returns the TupleDesc associated with this DbIterator.
   */
  public TupleDesc getTupleDesc();

  /**
   * Closes the iterator.
   */
  public void close();
}