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This page is an English extract of the German page GEDCOM/UID-Tag [1], for full details see the German page.

Name and Meaning




Unique ID for Records


Universal identification numbers (UUID) can be used to retrieve records even after further processing or export/import. A UUID claims to assign a unique and world wide for all times a value, so that no collisions takes place ( = multiple assignment of the same value ). The allocation of the UUID is decentralized and not coordinated by a superior system. The generation of UUID is described in RFC4122. UUID can only fulfill their function as long as they remain unchanged in export and import of GEDCOM files.

Due to the requirement of decentralized generation and free of collision UUID are complex and not suitable by the user for a directly identification feature. Their use is therefore concentrated for a comparison by programs, if two records have the same origin.

Formal Description of Permissible Values

Base: GEDCOM Standard Draft 5.5.1

This description contains information about the use of the user-defined tag _UID. An explicit representation is not included in the GEDCOM 5.5.1 standard.

PAF had at first introduced a user-defined identifier _UID, which has now been adopted by a number of programs.

Agreements for _UID

The agreements for _UID are derived from the discussion on the Gedcom-L. They were decided by a vote of the program authors of the list.

U0 Unique Identification of Records by _UID

For recognizing and tracking of records in GEDCOM files unique identifiers are used worldwide and unlimited in time. As value of the tag _UID a string that contains the identifier of the record will be exported.

U1 Use and Structure of _UID

The tag _UID may be used as often as {0:M} in each record, it is directly associated with the record on level 1. The first 36 characters of a _UID describing the identificator. If applicable, more existing characters are not significant.

U5 Recommendations for Generation and Use of 16 byte bit strings

  • During generation of the 16-byte bit string (UUID) it is recommended to create them according to version 1 or preferably version 4 of the standard protocol RFC 4122. Windows systems have access to CoCreateGuid().
  • At least for individual records _UID should be supported. Programs that support merging of records should support multiple _UID per record and keep all _UID unchanged.

Further Proposals and Discussions

There are several proposals and discussions, but no agreements reached so far.

For details see the German page GEDCOM/UID-Tag [2] items:

  • U6 _UID on Level 2 ( new )
  • U2 _UID and UUID
  • U3 Obtaining of _UID at Import/Export
  • U4 Modifications of _UID
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