Digital Preservation Technical Paper



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PUID Structure

A PUID is composed of two elements, the PUID type, and the actual identifier. The PUID type identifies the class of representation information to which the identifier refers, where each identifier is unique within that class. Thus, both elements are required to construct a unique identifier.


The syntax may be expressed in formal BNF notation as follows:

::=
‘/’

::= | ‘x-‘
::=
::= |
::= |
::= ‘a’ – ‘z’
::= ‘0’ - ‘9’
The PUID type is expressed as a lowercase alphanumeric string. The following PUID types are currently defined:


PUID type

Description

fmt

File format

Other types may be defined in the future. The identifier itself is expressed as a lowercase alphanumeric string of arbitrary length. The PUID type and identifier are separated by a forward slash.


An example PUID for a file format would therefore be expressed as follows:
fmt/42
PUID types prefixed by ‘x-‘ are used to provide temporary, private or experimental namespaces for that type. These may be used, for example, where a system requires a PUID identifier to be present which has not yet been formally assigned. Thus, format PUIDs of the type ‘x-fmt’ might be assigned for formats which have not yet been assigned an ‘fmt’ identifier. An ‘x-‘ PUID should not be considered persistent.


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