Information Technology Reference
In-Depth Information
Information
Object
Interpreted using
*
Representation
Information
Interpreted using
Data
Object
1
Physical
Object
Digital
Object
1
1..*
Bit
Fig. 7.3
Information object
grouped together in some form of order (that may or may not have meaning) this
will be described as the Logical Data Structure.
7.3.1 Physical Data Structure
7.3.1.1 The Bits
All digital data is composed of bits, which are simply zeros or ones. Their exact
physical representation is unimportant here, but can be the state of a magnetic
domain on a magnetic computer storage device (hard disk for example), a volt-
age spike in a wire etc., although as pointed out in Sect. 1.1 there is usually not a
one-to-one mapping between, for example, the magnetic domains or voltage spikes,
and bits. Digital data is just a sequence of bits, which, if the structure of those bits is
undefined, is meaningless to hardware, software or human beings. Bits are usually
grouped together to encode and represent some form of data value. Here we will use
the term “Primitive Data Types” (PDT) as the description of the structure of the bits
and “Data Value” (DV) as an instance of a given PDT in the data. The exact nature
of the structure of the different PDTs will be discussed in the following sections, but
for now we can summarise the PDTs in a simple diagram, see Fig. 7.4 .
As we can see from Fig. 7.4 there are (at least) ten PDTs. All other PDTs can that
can be found in digital data can be derived from these types (subclasses of Integer,
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