Data Definition Language. DDL is a type of database-specific
syntax used to define the structuring of schemas. Common DDL
Link items define a specific relationship between two object types. Link instances relate one object to one or more different objects.
More on links in Data Model.
An identifier that represents a set of values. It can be the name of an object type or an expression alias (defined in a statement WITH block or in the schema via an alias declaration. or a qualified schema name).
A path which begins with a set reference.