Every user-specified name that defines an element in a COBOL source element.
and is referenced in that source element
must be unique, either because no other name has the identical spelling and hyphenation, or because the name exists within a hierarchy of names such that references to the name can be made unique by mentioning one or more of the higher levels of the hierarchy. The higher levels are called qualifiers and the process that specifies uniqueness is called qualification. Enough qualification must be mentioned to make the name unique; however, it may not be necessary to mention all levels of the hierarchy.
In the Data Division, all data-names used for qualification must be associated with a level indicator or a level-number. Therefore, two identical data-names must not appear as entries subordinate to a group item unless they are capable of being made unique through qualification
or they are never referenced
. In the Procedure Division, two identical paragraph-names must not appear in the same section.
In the hierarchy of qualification, names associated with a level indicator are the most significant, followed by those names associated with level-number 01, followed by names associated with level-number 02 through 49. A section-name is the highest (and the only) qualifier available for a paragraph-name. Thus, the most significant name in the hierarchy must be unique and cannot be qualified. Subscripted or indexed data-names and conditional variables, as well as procedure-names and data-names, can be made unique by qualification. The name of a conditional variable can be used as a qualifier for any of its condition-names. Regardless of the available qualification, no name can be both a data-name and procedure-name.
Qualification is performed by following a data-name, a condition-name, a paragraph-name, or a text-name by one or more phrases composed of a qualifier preceded by IN or OF, which are logically equivalent.
When the resource named is a function, the function definition may require the user to specify in the reference to the function a value or set of values for one or more parameters which determine the value of the function for that particular reference. This is accomplished through the specification of arguments as described in the section Function-identifier.
if it is explicitly referenced within the source unit
Neither a paragraph-name nor a section-name need be unique, or capable of being made unique, unless explicitly referenced.
Qualified data-names can have up to five qualifiers.
Up to fifty qualifiers are permitted.
This restriction is not enforced.