A key is a set of one or more fields in a file that together uniquely identifies a record in that file. If you define a key, FileMan V.22.0 automatically enforces the integrity of that key, which means that:
1. No key field is null. 2. The key (that is, the combination of fields in a key) is unique for all records in the file.FileMan stores the definition of keys in the KEY file (#.31), which has the global root ^DD("KEY").