• Article Type: General
• Product: Aleph
• Product Version: 16.02

Description:
In the USM01 library, what is the advantage of using tab_expand_split to split a field when tab11 allows selective indexing of subfields?

From USM01 tab_expand_split
700## t A700 T700

From USM01 tab11_acc
700## 9 - AUT -efhklmnoprst4568 [this indexes the author subfields]
700## 9 - TIT -abcdehq4568 [this indexes the title subfields]
A700 AUT -e4568 [this indexes the author subfields]
T700 TIT [this indexes the title subfields]


In the USM01 library, what is the purpose of using tab_expand_extract to create two virtual fields, when each is indexed in the same index?

From USM01 tab_expand_extract
020## a a020
020## z z020

From USM01 tab11_ind
a020 020
z020 020

Resolution:
Both tab_expand_split and tab_expand_extract have the ability to handle multiple subfields of the same kind (multiple subfield z's; multiple subfield t's) as distinct pieces. If you don't use one of these, all the subfield z's or all of the subfield t's will be indexed in the same, single ACC or Direct index entry.

For instance, $$a12345678$$z13579864$$z24685310 would result in two index entries only:

12345678
13579864 24685310

With tab_expand_split or tab_expand_extract you can get three separate entries:

12345678
13579864
24685310

The difference between tab_expand_split and tab_expand_extract is that the latter has a column 4 which lets you limit the extraction to certain occurrences:

! Number of subfield occurrences for which the new virtual
! field is created. For example, it is possible to define
! that only the first occurrence of subfield $y in the
! 650 field should be used for the creation of the new field.

tab_expand_split has additional indicator control but has not been used much by North American sites; they have used tab_expand_extract.