The description of a logical model is based on the logical operators in the model. In Cascades, each logical operator takes 3 a fixed number of inputs. This fixed number is called the operator's arity .
Stored relations have persistence and are listed in the database catalog.
Tables are temporary collections 4 of tuples produced in the evaluation of a query. Tables are the output of GET and all other logical operators, and they are usually also the inputs to logical operators. These were not needed to represent the TPC-D queries. We say that an operator takes an input.