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R1166 / Generalization

Relational Action is a Table Action, Cardinality Action, or Extract Action

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In fact, we could say that all Relational Actions take a Non Scalar Flow as input and output either a Relation Flow or a Scalar Flow as output.

When we think of a Relational Action we generally think in terms of an action that inputs and outputs a Relation such that we can easily nest these Actions. We say that the corresponding relational operations are closed under the relation type. In the metamodel we refer to these (rightly or wrongly) as Table Actions to distinguish them from the small number of Actions that do not output a relation.

The Cardinality and Extract Actions, on the other hand, output a Scalar Flow. Cardinality counts the number of input tuples while Extract yields the value of some Table Attribute.