Information Technology Reference
In-Depth Information
particular Content Information. Examples of these systems include taxo-
nomic systems, reference systems and registration systems. In the OAIS
Reference Model most if not all of this information is replicated in Package
Descriptions, which enable Consumers to access Content Information of
interest.
The identifiers must be persistent and are referred to here as Persistent Identifiers,
and are unique in that an identifier should be usable to locate the specific digital
object with which it is associated, or an identical copy of that object.
We discuss first name spaces in general and then persistent identifiers in particu-
lar. This rather extensive discussion is a little out of place here but because PIDs are
not discussed in the implementation section this seemed the best location.
10.3.1 Name Spaces
There are many names spaces in the preservation environment covering, for exam-
ple, names for files, users, storage systems and management rules. Each of these
may change over time as information is handed over in the chain of preservation,
or as any single archive evolves. These name spaces, and their associated Access
Controls and Representation Information must themselves be managed.
10.3.2 Persistent Identifiers
Persistent Identifiers (PIDs) have been the cause of much debate, and there are many
proposed systems [
132
], including ARK [
133
], N2T [
134
], PURL [
135
], Handle
[
137
] and DOI [
138
]. To produce general purpose Persistent Identifiers, which could
be used to point to any and all objects, is well known to be challenging, the difficulty
being social rather than technological. On the other hand, given the increasing num-
ber of such systems, one might be led to think that at least some are technological
solutions in search of a problem. Indeed it sometimes seems that conferences and
discussions of PIDs are dominated by those offering solutions rather than by those
defining the problem.
A more limited type of Persistent Identifier is the Curation Persistent Identifier
(CPID) which was introduced in
Sect. 7.1.3
as pointing to Representation
Information.
It is relatively easy to generate a unique identifier by having a hierarchical
namespace,
x
.
y
.
z
each segment or namespace (i.e. each of x, y, z) forms a hierarchy of naming author-
ities, and where necessary to generate unique strings some algorithm such as that
used by the UUID [
138
] is used. A UUID is a Universal Unique IDentifier which is
a 128 bit number which can be assigned to any object and which is guaranteed to
