Unordered list sets and subsets retrieve data set records in physical order. There are no key items. Instead, the AA words which point to the data set records serve as the key; they are maintained in order by data set record address.
The structure for unordered list sets and subsets is identical to that for ordered list sets and subsets.
Unordered List Set and Subsets Restrictions
The only restriction on unordered list sets and subsets is that a FIND AT operation is not permitted since there is no key.
The reasons for the restriction are as follows:
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Disk space requirements for unordered list sets and subsets are the same as for ordered list sets and subsets, except that entries do not require space for the key.
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Tables for embedded structures are not shared between masters. Since the minimum table size is one segment, at least one segment is allocated for each master with details.
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FIND NEXT and FIND PRIOR operations access entries sequentially within each table, and then follow the link to the next table. Entries are returned in physical data set order.
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Unordered list sets and subsets are not recommended for use as disjoint structures, and they are not useful for unordered data sets.
