A LOB or XML locator variable is a variable
that contains the locator representing a LOB or XML value on the application
server.
LOB or XML locator variables can be defined
in the following host languages:
PL/I (LOB only)
See Manipulating large objects with locators for information
about how locators can be used to manipulate LOB and XML values.
A locator variable in an SQL statement must
identify a LOB or XML locator variable described in the program according
to the rules for declaring locator variables. This is always indirectly
through an SQL statement. For example, in C: 
static volatile SQL TYPE IS CLOB_LOCATOR *loc1;
Like all other variables, a LOB or XML locator
variable can have an associated indicator variable. Indicator variables
for LOB or XML locator variables behave in the same way as indicator
variables for other data types. When a null value is returned from
the database, the indicator variable is set and the variable is unchanged.
When the indicator variable associated with a LOB or XML locator is
null, the value of the referenced LOB or XML is null. This means that
a locator can never point to a null value.
If a locator variable does not currently represent any value, an error occurs when the locator variable is referenced.
At transaction commit or any transaction termination,
all LOB or XML locators that were acquired by the transaction are
released.
It is the application programmer's
responsibility to guarantee that any LOB or XML locator is only used
in SQL statements that are executed at the same application server
that originally generated the LOB or XML locator. For example, assume
that a LOB locator is returned from one application server and assigned
to a LOB locator variable. If that LOB locator variable is subsequently
used in an SQL statement that is executed at a different application
server, unpredictable results will occur.