Information Technology Reference
In-Depth Information
Another type of logical expression could be the identification of an element with
a specific DV. For example, in the FITS format there are several different structures
where each is identified by a keyword (String), so here an expression must exist that
compares the value of the string against a lists of possible values. If it matches one
then the appropriate structure is selected. Integer values are another possible DV
that can be used for selecting structures.
7.3.3 Summary of Some Requirements for Structure
Representation Information
From the above we can summarise the some of the important characteristics (prop-
erties) of data that form Structure RepInfo. It will be shown later that some existing
formal languages capture some of these properties allowing one to form detailed
and accurate Structure RepInfo that can be validated against the data and used in an
automated way.
1. Physical Structure Information
1. Endienness of the data (big-endian or little endian).
2. Character type
1. endienness.
2. character set used.
3. size in octets/bits.
3. Integers
1. endienness.
2. size in octets/bits.
3. signed/unsigned.
4. location of signed bit.
5. interpretation method - two's compliment etc.
6. restriction on maximum and minimum size.
7. fixed number of values.
4. Real floating point numbers
1. endienness.
2. location and structure of the significand bits.
3. location and structure of the exponent bits.
4. normalised.
5. interpretation method of significand - two's compliment etc.
6. bias scheme for exponent.
7. reserve values/exceptions.
8. location of signed bit.
9. formula for interpreting the number.
10. restriction on maximum and minimum size.
11. fixed values.
