====== 831 Duplicate control field (O;R) ======


==== Field Definition and Scope ====

This field is used for database updating purposes only. It shall not be displayed in the WWW interface, nor shall its content be edited by a cataloguer. 


==== Application of Content Designators ====

=== Indicators ===

**Indicator 1:** none

**Indicator 2: Specifies the type of duplicate reference:**

  * **0**  The record indicated in $a was reviewed by a cataloger and merger of the current and the indicated record into one is deprecated.

  * **1**  The record indicated in $a is probably a duplicate to the present record and should therefore be revised by a cataloguer.

  * **2**  The record indicated in $a will be merged to the present record in an updating process, since a cataloguer has considered it referring to the same entity.

=== Subfields ===

**$a Record Identifier (M;NR)**\\
Record ID of the record considered duplicate

**$b Similarity (O;NR)**\\
Any similarity measure, suitable to support the decision whether the two records should be merged or not


==== Input Conventions ====
This field is usually added during automatic data ingest.

For an instruction on how to use it to merge records that have not been flagged as possible duplicates manually see [[::resources:cerl_thesaurus:editing:mergingunmarked|How to merge records which have not been marked for deduplication]]


==== Examples ====

  - 831 #1$acnp00081480

==== Internal Representation ====
<code javascript>
{"meta": {
    "distinctFrom": ["Record ID ($a)"],
    "sameAs": ["Record ID ($a)"],
    "possibleMatch": [{
        "id": "Record ID ($a)",
        "similarity": "Similarity ($b)"
    }]
}}
</code>

==== Change History ====
  * //17.07.2017//: Subfields $8, $n and $z are no longer supported, once the CT has been migrated into its new environment