ca.uqac.dim.turtledb

Class Relation

java.lang.Object

ca.uqac.dim.turtledb.Relation

Direct Known Subclasses:

BinaryRelation, NAryRelation, Table, UnaryRelation

public abstract class Relation
extends java.lang.Object

A relation is implemented as a map from a set of tuples (the relation's key) to a set of tuples

Author:

sylvain

Field Summary

Fields

Modifier and Type	Field and Description
boolean	m_streamingMode Whether the enumeration of the relation's tuples is performed in "streaming" mode (vs.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Relation() Empty constructor.

Method Summary

Modifier and Type	Method and Description
abstract void	accept(QueryVisitor v)
abstract RelationIterator	cacheIterator() Returns an iterator over tuples of the relation
boolean	contains(Tuple tup) Determines if a relation contains a given tuple.
int	getCardinality() Computes the cardinality of a relation.
int	getDegree() A relation's degree is the size of its schema.
abstract Schema	getSchema() Returns the relation's schema
boolean	isFragment() Determines if the query tree is a fragment.
boolean	isLeaf() Determines if a given operator is at the leaf of the query tree.
RelationIterator	iterator()
void	setStreamingMode(boolean b) Sets the way of querying the relation's tuples
abstract RelationIterator	streamIterator() Returns an iterator over tuples of the relation
java.lang.String	toString() Pretty-prints a relation to a string
abstract int	tupleCount() Returns the number of actual tuples present in the query.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

m_streamingMode

public boolean m_streamingMode

Whether the enumeration of the relation's tuples is performed in "streaming" mode (vs. "cache" mode)

Constructor Detail

Relation

protected Relation()

Empty constructor. Should only be called from children's constructors.

Method Detail

getSchema

public abstract Schema getSchema()

Returns the relation's schema

Returns:

The schema

getDegree

public final int getDegree()

A relation's degree is the size of its schema.

Returns:

The relation's degree

setStreamingMode

public void setStreamingMode(boolean b)

Sets the way of querying the relation's tuples

Parameters:

b - True to evaluate in streaming mode, false otherwise

iterator

public final RelationIterator iterator()

toString

public java.lang.String toString()

Pretty-prints a relation to a string

Overrides:

toString in class java.lang.Object

accept

public abstract void accept(QueryVisitor v)
                     throws QueryVisitor.VisitorException

Throws:

QueryVisitor.VisitorException

getCardinality

public int getCardinality()

Computes the cardinality of a relation. Except for instances of Table (which actually contain concrete tuples), calling this method will trigger the evaluation of the query tree and the enumeration of all tuples. It should be used sparingly.

Returns:

The number of tuples in the relation

tupleCount

public abstract int tupleCount()

Returns the number of actual tuples present in the query. This number is different from the cardinality of the query; it counts the number of tuples that are present in the leaves of the query tree.

Returns:

The tuple count

contains

public boolean contains(Tuple tup)

Determines if a relation contains a given tuple. Warning #1: this implementation is inefficient, as it enumerates all tuples until found. Warning #2: using contains resets any undergoing enumeration made on the relation.

Parameters:

tup - The tuple to look for

Returns:

True if the tuple is present, false otherwise

streamIterator

public abstract RelationIterator streamIterator()

Returns an iterator over tuples of the relation

Returns:

cacheIterator

public abstract RelationIterator cacheIterator()

Returns an iterator over tuples of the relation

Returns:

isFragment

public boolean isFragment()

Determines if the query tree is a fragment. This is the case when the tree's root is a VariableTable.

Returns:

True if the query tree is a fragment, false otherwise

isLeaf

public boolean isLeaf()

Determines if a given operator is at the leaf of the query tree. Only instances of Table and VariableTable may be leaves.

Returns: