Glossary of Terms

kernel

A public function which describes one or more transformations on a set of data.

expression

Typically refers to a SQL expression; takes as input one or more columns and, through a series of operations, produces either a scalar value or a column value.

target

An expression whose value is returned to the user as part of a projection.

fragment

A row-wise striping across all columns in a table in a fixed unit (32,000,000 rows by default). See Columnar Data Organization for more information.

chunk

The intersection of a fragment and a column. A single chunk is a series of rows from one column in a table and is uniquely identified by the chunk key, a tuple consisting of database ID, table ID, column ID, and fragment ID.