Information Technology Reference
In-Depth Information
Definition 1. implies that if the users of a community know a set of modules they
also know how to perform tasks on them. However the performability of tasks is
represented with dependencies. According to Axiom 1 the dependencies of a module
are always the same. So the knowledge of a module from a user implies, through
the dependency graph, the knowledge of its dependencies as well, and therefore the
knowledge of performing various tasks with the module.
In our example this means that since astronomers know the module
FITS
S/W
, they know how to run this application, so they know the dependency
FITS S/W > JVM
. So if we want to find all the modules that are understand-
able from the users of a DC profile, we must resolve all the direct and indirect
dependencies of their known modules (
T(u)
). For example the modules that are
understandable from astronomers are {
FITS Documentation, FITS S/W,
FITS Dictionary, PDF Reader, JVM, XML Viewer
}, however their
DC profile is a subset of the above modules.
This approach allows us to reduce the size of DC profiles by keeping only the
maximal modules (maximal with respect to the dependency relation) of every DC
profile. Therefore we can remove from the DC profile modules whose knowledge
is implied from the knowledge of an “upper” module and the dependency graph.
For example if the astronomers profile contained also the module
JVM
then we
could safely remove it since its knowledge from astronomers is guaranteed from
the knowledge of
FITS S/W
.
We will discuss the consequences of not making the assumption expressed in
Axiom 1, later in Sect.
8.2.5
.
8.2.3 Intelligibility-Related Preservation Services
8.2.3.1 Deciding Intelligibility
Consider two users
u
1
,
u
2
who want to render (play) the music encoded in an
mp3 file. The user
u
1
successfully renders the file while
u
2
does not recognize it
and requests its direct dependencies. Suppose that the dependency that has been
recorded is that the mp3 file depends (regarding renderability) on the availability of
an mp3-compliant player, say
Winamp
. The user is informed about this dependency
and installs the application. However he claims that the file still cannot be rendered.
This happens because the application in turn has some other dependencies which are
not available to the user, i.e.
Winamp > Lame_mp3
. After the installation of this
dependency, user
u
2
is able to render the file. This is an example where the ability
to perform a task depends not only on its direct dependencies but also on its indirect
dependencies.
This means that to decide the performability of a task on a module by a user,
we have to find all the necessary modules by traversing the dependency graph and
then to compare them with the modules of the DC profile of the user. However the
disjunctive nature of dependencies complicates this task. Disjunctive dependencies
express different ways to perform a task. This is translated in several paths at the
