Ya existe el manejo de Assertions en postreSQL 7.4 o version superior?

Saludos listeros,

Quisiera saber si Ya existe el manejo de Assertions en postreSQL 7.4 o version superior?
lei en esta pagina que todavia no, pero si tienen informacion les agradezco:

http://www.redhat.com/docs/manuals/database/RHDB-7.1.3-Manual/sql/sql-createtable.html
CONSTRAINT clause SQL92 specifies some additional capabilities for constraints, and also defines assertions and domain constraints.
An assertion is a special type of integrity constraint and shares the same namespace as other constraints. However, an assertion is not necessarily dependent on one particular table as constraints are, so SQL-92 provides the CREATE ASSERTION statement as an alternate method for defining a constraint:

CREATE ASSERTION name CHECK ( condition )

Gracias:

Tania

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