If a persistent class uses %Storage.Persistent then the USEEXTENTSET parameter is used to
specify the global naming strategy used by the default storage class (%Storage.Persistent).
If TRUE, then global names are generated for each index that is not already allocated a LOCATION in the active
If the storage definition specifies EXTENTLOCATION then that value is used as the base reference for all globals
assigned to indices that do not have an explicit LOCATION assigned.
The global name generator for USEEXTENTSET = TRUE honors the package prefix defined
in the Package Definition. If none is defined then the package prefix is generated using a based-62 encoded integer
produced from CRC32 of the package name. The specific class identifier is generated from the unqualified class name using
the same hash (class->crc32->base62) to form EXTENTLOCATION. Specific index suffixes are produced using a generated
offset that is local to the first persistent class with an enumerated extent in which the index appears (either defined or inherited).
There are several factors that influence the generation of EXTENTLOCATION:
The EXTENTLOCATION value is used as the base for specific globals allocated to indices. Each index is assigned an offset that is incremented from
1 by 1, offset = 1 is reserved for the IDKEY index.
- If the EXTENTLOCATION keyword is defined then its value is used,
- If the DEFAULTGLOBAL class parameter is defined then its value is used,
- otherwise, the value is generated as two dot delimited segments. The first segment is either the defined package prefix retrieved from
the package definition global or, if none is defined, a hash of the package name. The second segment is generated by a hash of the unqualified
class name. The hash used is a base 62 encoded CRC32 of the value. For example, Sample.Person produces ^EW3K.wPC9 if no package prefix is defined.
EXTENTLOCATION is specific to each class. When a persistent class extends another persistent class, forming a subextent, then the subclass's EXTENTLOCATION
is specific to that subclass. The index location for any inherited index is already defined specifically in the super class so the subclass's EXTENTLOCATION
will only be used as the base for any index that originates in the subclass. For example, Sample.Employee extends Sample.Person. The EXTENTLOCATION generated for
Sample.Person is ^EW3K.wPC9 and the EXTENTLOCATION for Sample.Employee is ^EW3K.D1Ex. Since Sample.Employee inherits several indices from Sample.Person, the
global name assigned to each of those indices is already defined and inherited by Sample.Employee. However, any index defined in Sample.Employee and not
inherited from Sample.Person will be assigned a global name based on Sample.Employee's EXTENTLOCATION, not on Sample.Person's EXTENTLOCATION. In other words,
the EXTENTLOCATION storage keyword is not inherited.
The following tables show the indices and locations for Sample.Person and Sample.Employee. Notice the last index in the Sample.Employee table:
|Class = Sample.Person|
|Class = Sample.Employee extends Sample.Person|
Any generated global index locations and EXTENTLOCATION are updated back into the active storage definition after the class is
If USEEXTENTSET is FALSE, then global names are generated using the package-hash.class-hashSuffix strategy.
For example, ^Sample.PersonD and ^Sample.PersonI("SSNKey") are globals used by Sample.Person and specific index structures
are all stored in ^Sample.PersonI with the index name used as the first subscript.