A SuperFile may contain INDEX files instead of DATASET files, making it a SuperKey. All the same creation and maintenance processes and principles apply as described previously in the Creating and Maintaining SuperFiles article.

However, a SuperKey may not contain INDEX sub-files that directly reference the sub-files of a SuperFile using the {virtual(fileposition)} "record pointer" mechanism (used by FETCH and full-keyed JOIN operations). This is because the {virtual(fileposition)} field is a virtual (exists only when the file is read from disk) field containing the relative byte position of each record within the single logical entity.

The following attribute definitions used by the code examples in this article are declared in the DeclareData MODULE structure attribute:

EXPORT i1name := '~PROGGUIDE::SUPERKEY::IDX1';
EXPORT i2name := '~PROGGUIDE::SUPERKEY::IDX2';
EXPORT i3name := '~PROGGUIDE::SUPERKEY::IDX3';
EXPORT SFname := '~PROGGUIDE::SUPERKEY::SF1';
EXPORT SKname := '~PROGGUIDE::SUPERKEY::SK1';
EXPORT ds1 := DATASET(SubFile1,{Layout_Person,UNSIGNED8 RecPos {VIRTUAL(fileposition)}},THOR);
EXPORT ds2 := DATASET(SubFile2,{Layout_Person,UNSIGNED8 RecPos {VIRTUAL(fileposition)}},THOR);
EXPORT i1 := INDEX(ds1,{personid,RecPos},i1name);
EXPORT i2 := INDEX(ds2,{personid,RecPos},i2name);
EXPORT sf1 := DATASET(SFname,{Layout_Person,UNSIGNED8 RecPos {VIRTUAL(fileposition)}},THOR);
EXPORT sk1 := INDEX(sf1,{personid,RecPos},SKname);
EXPORT sk2 := INDEX(sf1,{personid,RecPos},i3name );