Information Technology Reference
In-Depth Information
understanding and validating the data, can also allow or aid the reproduction of
the final data products. [
110
] proposes an extended framework for file systems that
allows users to define dependency links between files where the semantics of these
links are defined by users through key-value pairs. Finally, many dependency man-
agement approaches for software components [
111
-
115
] have been described in
the literature. The interpretation of software dependencies varies and concerns the
installation or de-installation safety, the ability to perform a task, the selection of
the most appropriate component, or the consequences of a component's service call
to other components.
8.1.1 OAIS - Preserving the Understandability
As outlined in Chap.
3
,
Data Objects
are considered in OAIS to be either physical
objects (objects with physically observable properties) or digital objects. Every Data
Object along with some extra information about the object forms an
Information
Object
. Following OAIS, information is defined as any piece of knowledge that is
exchangeable and can be expressed by some type of data. For example the informa-
tion in a Greek novel is expressed as the characters that are combined to create the
text. The information in a digital text file is expressed by the bits it contains which,
when they are combined with extra information that interprets them (i.e. mapping
tables and rules), will convert them to more meaningful representations (i.e. charac-
ters). This extra information that maps a Data Object into more meaningful concepts
is called Representation Information (RI). It is a responsibility of an OAIS to find
(or create new) software conforming to the given Representation Information for
this information object.
We note that the notion of interpretation as stated by OAIS is more restricted
than the general notion of dependency. Dependencies can be exploited for capturing
the required information for digital objects not only in terms of their intelligibil-
ity, but also in terms of validity, reproducibility or functionality (if it is a software
application).
8.2 A Formal Model for the Intelligibility of Digital Objects
8.2.1 A Core Model for Digital Objects and Dependencies
We introduce here a core model for the intelligibility of digital objects based on
dependencies. The model has two basic notions: Module and Dependency. As we
described in Sect.
8.1
, digital objects depend on a plethora of other resources. Recall
that these resources can be described as objects containing information or using
other resources. We use the general notion of module to model these resources (in
our examples either exchange or computational objects). There is no standard way
to define a module, so we can have modules of various levels of abstraction, e.g.
