Information Technology Reference
In-Depth Information
Inevitably there can never be an absolutely complete set of definitions for
RepInfo about data in general. This is simply due to the fact that data is so varied
and complex.
Here we provide further details of the basic techniques. Most of these charac-
teristic have been gained by studying many data sets and formal data description
languages.
Once the abstract notions about a particular type of RepInfo have been described,
then existing tools and standards are described that may help you in creating RepInfo
if you discover that your existing RepInfo is inadequate for your purposes (or non-
existent). Most of these tools do not attempt to create a perfect collection of RepInfo,
and we will try to highlight what they can and cannot describe. Most of the tools
generate RepInfo in accordance to some formal standard and format. As noted sev-
eral times above, this has advantages that when the RepInfo comes to be used; it
allows the data to be used much more easily than if one just had the traditional
“informal” documentation.
The OAIS layered information model (Fig.
7.2
) gives a high level view which is
quite useful at this point.
This model is in an appendix of the OAIS Reference Model and as such is not
part of that standard. However it contains a number of useful ideas, including:
•
The Media Layer simply models the fact that the bit strings are stored on physical
or communications media as magnetic domains or as voltages. The function of
this layer is to convert that bit representation to the bit representation that can
be used in higher level (i.e., 1 and 0). This layer has as single interface, which
Application Layer (Analysis and Display Programs)
Objective Interface
Message
Named Aggregates
Named Bit Streams
...
Object Layer
Data Objects
Container Objects
Data Description Objects
Named Aggregate
...
Structure Layer
Primitive data types
List/Array types
Records
Names Aggregates
Named Bit Stream
Named Bit Stream
...
Stream Layer
Delimited Byte Streams
Media Layer (Disks, Tapes and Network)
Fig. 7.2
OAIS layered information model
