Information Technology Reference
In-Depth Information
dependency graph, and we must find at least one such path that is intelligible by the
user. The problem becomes more complicated due to the properties (e.g. transitiv-
ity) that dependencies may have (which can be specified using rules as described
in Sect.
8.2.1.1
). On the other hand, if all dependencies are conjunctive, then the
required modules obtained from the dependency graph are unique.
Below we describe methods for deciding the intelligibility of an object for two
settings; the first allows only conjunctive dependencies, while the second permits
also disjunctive dependencies.
Conjunctive Dependencies
If dependencies are interpreted conjunctively the module requires the existence of
all its dependencies for the performability of a task. To this end we must resolve all
the dependencies transitively, since a module
t
will depend on
t
, this in turn will
depend on
t
etc. Consequently we introduce the notions of required modules and
closure.
•
The set of modules that a module
t
requires in order to be intelligible is the set
Nr
+
(
)
=
t
t
>
+
t
t
•
The closure of a module t, is the set of the required modules plus module t.
Nr
∗
(
Nr
+
(
t
)
= {
t
} ∪
t
)
The notation
>
+
is used to denote that we resolve dependencies transitively. This
means that to retrieve the set
Nr
+
(t) we must traverse the dependency graph start-
ing from module
t
and recording every module we encounter. For example the set
Nr
+
(
mars.fits) in Fig.
8.5
will contain the modules {
FITS Documentation,
FITS S/W, FITS Dictionary, PDF Reader, JVM, XML Viewer
}.
This is the full set of modules that are required for making the module
mars.fits
intelligible.
In order to decide the intelligibility of a module
t
with respect to the DC profile
of a user
u
we must examine if the user of that profile knows the modules that are
needed for the intelligibility of
t
.
Definition 2
A module
t
is intelligible by a user
u
, having DC profile
T(u)
iff its
required modules are intelligible from the user, formally
Nr
+
(
t
)
⊆
Nr
∗
(
T
(
u
))
Recall that according to Axiom 1 the users having profile
T(u)
, will understand
the modules contained in the profile, as well as all their required modules. In other
words they can understand the set
Nr
∗
(T(u)).
For example the module
mars.fits
is intelligible by astronomers (users hav-
ing the profile u
1
) since they already understand all the modules that are required
for making
mars.fits
intelligible, i.e. we have:
Nr
+
(
mars
.
fits
)
Nr
∗
(
⊆
T
(
u
1
))
.
