During the compilation, the PL/SQL compiler relates identifiers like the name of a variable with an address or memory location, actual value, or datatype. This process is termed as the binding. The relationship lasts through all the successive executions until the recompilation occurs, which may cause the rebinding.
Before binding the names, the PL/SQL should solve all the references to them in the compilation unit. This process is known as the name resolution. The PL/SQL considers all the names to be in the same namespace. Therefore, one declaration or definition in an inner scope can hide the other in an outer scope. In the illustration below, the declaration of the variable client hides the definition of the datatype Client as the PL/SQL is not case sensitive apart from within the string literals:
TYPE Client IS RECORD (...);
TYPE Customer IS RECORD (...);
client Customer; -- hides definition of type Client
-- in outer scope
lead1 Client; -- illegal; Client resolves to the
-- variable client
lead2 block1.Client; -- OK; refers to type Client
Though, you can still refer to the datatype Client by qualifying the reference with the block label block1.
In the CREATE TYPE person1 statement below, the compiler solves the second reference to the manager as the name of the attribute you are trying to declare. In the CREATE TYPE person2 declaration, the compiler solves the second reference to the manager as the name of the attribute you merely declared. In both the situation, the reference to the manager generates an error as the compiler expects a type name.
CREATE TYPE manager AS OBJECT (dept NUMBER);
CREATE TYPE person1 AS OBJECT (manager manager);
CREATE TYPE person2 AS OBJECT (manager NUMBER, mgr manager);