When a heading splits and becomes 2 or more headings, MARS 2.0 programs can either replace the obsolete heading in the bibliographic record with all of the new headings, or leave the old heading in the record.
Subject heading in bibliographic record:
650 0 $a$aNurses and nursing$xEffect of managed care on.
Replaced by two split headings:
650 0 $a$aNurses$xEffect of managed care on.
650 0 $a$aNursing$xEffect of managed care on.
Subfield $a matches obsolete forms of the heading (4XX fields) in 2 authority records, sh 85093349 (Nurses) and sh 85093362 (Nursing). If a library elected to have split headings replaced by all new headings the bibliographic heading would be replaced by the 2 headings above.
Many libraries find that patrons have difficulty distinguishing between the new variants of a split heading and often search for the concept under the incorrect term. Therefore, most libraries choose to have all split headings inserted in the bibliographic record. Indicate if you would like “split” headings replaced by all the new headings.
Split Heading Reports Available
For libraries choosing to insert split headings into the bibliographic record, a report of splits inserted is available (see Step 5, report R31). If obsolete headings should be retained, a report of headings which match multiple authority records is also available (see Step 5, report R17).
When MARS 2.0 Authority Control is completed, a small number of bibliographic records may contain duplicate headings. A heading may have been updated to a form already in the bibliographic record, or two different headings may both update to the same form.
The final step in every MARS 2.0 Authority Control Project is duplicate field resolution (“deduping”) of all authority controlled headings to ensure that headings in your bibliographic records will be unique. MARS 2.0 deduping compares heading text character by character. For example, a 650 field with a second indicator of 0 (LC subject heading) and a 650 field with a second indicator of 2 (MeSH subject heading) are not considered duplicates.
If the normalized bibliographic heading does not match a normalized established heading in an authority record, the heading is unmatched. A report of all unmatched bibliographic headings is available for you to review (see Step 5, report R07). You can use the report to make additional corrections to bibliographic headings in your local system.
MARS 2.0 also creates a brief authority record out of the unmatched heading and tries to match against the national authority database during Notification services (see Step 6 of the Planning Guide). If a match is then found a new authority record is delivered to the library (see Ongoing Services in Step 6 for more details).
Alternatively, the MARS 2.0 staff can manually review bibliographic headings which do not match an authority record (see Manual Review in Step 7.2 of the Planning Guide).
Duplicate NAF and SAF Records
LC has undertaken a multi-year effort to establish each heading in either the Name Authority File or the Subject Authority File, but not in both. In mid-1999, a MARS 2.0 study of the LC authority files found no duplicate NAF/SAF records. If duplicate records were encountered, MARS 2.0 would distribute the records differently depending on the authority file segmentation you select. MARS 2.0 processing will always take/return the larger authority record.