be.SIRAPRISE.ra

Class TRANSFORM

java.lang.Object

be.SIRAPRISE.ra.RelationalOperator

be.SIRAPRISE.ra.TRANSFORM

public abstract class TRANSFORM
extends RelationalOperator

The TRANSFORM operator. An invocation of TRANSFORM is equivalent to a longer expression involving PROJECT, EXTEND and RENAME as follows : Transform takes two arguments : the first being a relational expression, and the second a list of transform specs. So an invocation of TRANSFORM looks like TRANSFORM(<Relational Expression>,(<transform spec list>)). <transform spec list> is a list of attribute computation specifications, an attribute computation specification mentioning the attribute name for the relation produced, and an expression defining how to compute the value for a particular tuple in the result. So a transform spec looks like <AttributeName>(<Expression>). The expression can be omitted, in which case it defaults to <AttributeName>. The resulting relation has all and exactly those attributes in its heading that are mentioned in the transform spec list. The value for each of those attributes is the value obtained by evaluating the expression corresponding to the attribute name in the transform spec list. TRANSFORM thus "bundles" the semantics of EXTEND, RENAME and PROJECT as follows :

• It "adds" the attributes that are specified as ATTRIBUTENAME(some operator invocation) just as EXTEND does
• It "removes" the attributes that are not specified just as PROJECT does
• It "alters" the names of the attributes that are specified as ATTRIBUTENAME(OTHERATTRIBUTENAME) just as RENAME does

Note that TRANSFORM is effectively implemented as the invocation of some projection of some extension of the input expression : TRANSFORM(R,...) === PROJECT(EXTEND(R,...),(...)), in which the first ellipsis stands for all <transform spec>s that include an expression, and the second for all attribute names mentioned in any <transform spec>. This implies that all the semantical rules of extend and project apply INDIVIDUALLY. In particular : this makes transform specs such as A(PLUS(A,A)) invalid because that would make an attribute named 'A' appear twice in the result of the extend. Note also that while A(B) is valid as a transform spec (achieving the same result as RENAME if attribute B is not mentioned), the combination A(B)B(A) is invalid, while this same combination in an invocation of RENAME is valid (thereby achieving the result of the two attributes "swapping" values).

Author:

Erwin Smout

Constructor Summary

Constructors

Constructor and Description
TRANSFORM()

Method Summary

Modifier and Type	Method and Description
int	getMaximumArgumentCount() Gets the maximum argument count for this operator.
int	getMinimumArgumentCount() Gets the minimum argument count for this operator.
java.lang.String	getName() Gets the operator name
boolean	isMonoRelationOperator() Checks if the operator takes only one Relation as input

Methods inherited from class be.SIRAPRISE.ra.RelationalOperator

toString

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

TRANSFORM

public TRANSFORM()

Method Detail

getMaximumArgumentCount

public final int getMaximumArgumentCount()

Description copied from class: RelationalOperator

Gets the maximum argument count for this operator. Note that stuff like rename lists are regarded as an argument as far as this count is concerned

Specified by:

getMaximumArgumentCount in class RelationalOperator

Returns:

the maximum argument count for this operator.

getMinimumArgumentCount

public final int getMinimumArgumentCount()

Description copied from class: RelationalOperator

Gets the minimum argument count for this operator. Note that stuff like rename lists are regarded as an argument as far as this count is concerned

Specified by:

getMinimumArgumentCount in class RelationalOperator

Returns:

the minimum argument count for this operator

getName

public final java.lang.String getName()

Description copied from class: RelationalOperator

Gets the operator name

Specified by:

getName in class RelationalOperator

Returns:

the operator name

isMonoRelationOperator

public final boolean isMonoRelationOperator()

Description copied from class: RelationalOperator

Checks if the operator takes only one Relation as input

Specified by:

isMonoRelationOperator in class RelationalOperator

Returns:

true if the operator takes only one Relation as input