Symbols and Aliases
Tuesday, February 22, 2011
1:09 PM
Aliases in Pig Latin
Each  symbol is an alias that represents a relation to be computed.
A relation has rows/records/tuples and columns/fields. 
Columns/fields may be named or unnamed.
If they are unnamed, one may refer to them as $0, $1, $2.... 
They are always named when the relation is being constructed; you cannot go back and name them "later". 
Relations cannot be changed after they are constructed; new relations can be created. 