Information Technology Reference
In-Depth Information
system or a community of users can be said to have a
Knowledge Base
which allows
them to understand received information. For example, a person whose Knowledge
Base includes the Greek language will be able to understand a Greek text. We
can use a similar approach to limit the long chain of dependencies that have to
be recorded.
A Designated Community is an identified group of users (or systems) that is able
to understand a particular set of information, and a DC Knowledge is the informa-
tion that is assumed to be known by the members of that community. OAIS only
makes implicit assumptions about the community Knowledge Base. However here
we can make these assumptions
explicit
by assigning to the users of a community
the modules that are assumed to be known from them. To this end we introduce the
notion of DC Profiles.
Definition 1
If
u
is a DC (Designated Community), its profile, denoted by
T(u),
is the set of modules assumed to be known from that community.
As an example, Fig.
8.5
shows the dependency graph for two digital objects,
the first being a document in PDF format (
handbook.pdf
) and the second a
fileinFITSformat(
mars.fits
). Moreover two DC profiles over these mod-
ules are defined. The first (the upper oval) is a DC profile for the community of
astronomers and contains the modules
T(u
1
)
{
FITS Documentation, FITS
S/W, FITS Dictionary
} and the other (lower oval) is defined for the com-
munity of ordinary users and contains the modules
T(u
2
)
=
{
PDF Reader, XML
Viewer
}. This means that every astronomer (every user having DC profile
u
1
)
understands the module
FITS S/W
, in the sense that he/she knows how to use this
software application.
We can assume that the graph formed by the modules and the dependencies is
global in the sense that it contains all the modules that have been recorded, and we
can assume that the dependencies of a module are always the same
=
Axiom 1
Modules and their dependencies form a dependency graph
).
Every module in the graph has a unique identifier and its dependencies
are always the same.
G
=
(
T
,
>
Fig. 8.5
DC profiles example
