Structural transformations
Tuesday, February 22, 2011
4:04 PM
Several operations change the structure of data:
Functions: 
COUNT(bag or tuple) returns the number of tuples in a bag, or the number of fields in a tuple. 
FLATTEN(bag or tuple) removes hierarchy from a bag or tuple.
Statements: 
GROUP-BY: put similar things into bags. 
JOIN-BY: combine two relations via a common key. 