Information Technology Reference
In-Depth Information
be unique. The mechanism used to guarantee uniqueness is through combinations
of hardware addresses, time stamps and random seeds.
The difficulty task is to make the link between the identifier (as a character string)
to the object to which it points. In particular the bootstrap procedure must be in
place, in other words given a string - how does one know what to do with it - where
does one start?
The steps involved would be
1. given “x.y.z” one somehow knows (i.e. the bootstrap step) that one uses some
service “X” with which one can find out what “x” means i.e. tells one where to
go to look up some service (“Y”) associated with “x”. “X” will be referred to
here as the bootstrap resolver service
2. using service “Y” we then find out something about “y” - in particular some
service “Z”
3. using service “Z” we then find out something about “z” - in particular some
service “T” which will point, at last, to the object wanted. This will be referred
to here as the terminal resolver service
We presumably can say have some control about the last service “T”. On the other
hand we may have no control over the others in the hierarchy.
Thus we have the issues of:
1.
the bootstrap into the name resolution system
2.
the persistence of each of the name resolvers
We look at these issues in a little bit more detail, and use our old friend
recursion
.
Figure
10.2
indicates a PID “
ABC:xyz/abc/def/xxx
” (here we use “/” as the name-
space separator rather than “.”)
This PID is a String embedded in some Digital Object; it requires some
Representation Information to allow it to be understood and used. This
Representation Information tells one that one should use a particular root names
resolver. This then unpacks the next part of the PID and so on until one gets to the
correct repository.
Thinking about this from a more abstract point of view one can say:
•
name resolvers contain digital information - the association between a String and
a pointer to the next name resolver
•
this information must be preserved if we are to have persistence
Therefore each name resolver should be regarded as an archive - an OAIS - illus-
trated in Fig.
10.3
. This allows us to apply all the OAIS concepts to them, including
audit and certification, which would require, for example, that each has handover
plans.
