Delta members can be distinguished from non-delta members not only on account of their efficient storage form but because of the unique relationship that exists among delta members.
Storage space is saved due to the delta structure:
Redundant records of a member with respect to the predecessor member can be identified and will not be stored again.
For records to be identified as redundant a formal comparison is made between the records of the new version and the specified base version.
Unique relationships are established via:
Unique member names
Delta members that are interrelated have the same member name and thus form a range of names. For this reason, non-delta members and delta members must have different member names, which means thata non-delta member is created only if no delta member exists that has the same name,
a delta member is created only if no non-delta member exists that has the same name.
All delta members having the same name form exactly one logically structured “delta tree” which in its simplest form is a “delta sequence”.
One name is associated with exactly one delta tree.
Unique version designations
When a member is included as a delta member, It is possible to specify which member is the predecessor member, i.e. which member is to be used as the basis for comparison. The default is BASE=*STD.
The conventions for member names and version designations that are established when members are added cannot be subsequently altered, for reasons of auditing and consistency. A new delta tree, if required, may be created by copying and simultaneously renaming the existing delta tree.