Data Representation

13.1 User-defined data types

Candidates should be able to:

1. Show understanding of why user-defined types are necessary

2. Define and use non-composite types

Notes and guidance

Including enumerated, pointer

3. Define and use composite data types

Notes and guidance

Including set, record and class/object

4. Choose and design an appropriate user-defined data type for a given problem

Candidates should be able to:

1. Show understanding of the methods of file organisation and select an appropriate method of file organisation and file access for a given problem

Notes and guidance

Including serial, sequential (using a key field), random (using a record key)

2. Show understanding of methods of file access

Notes and guidance

Including

Sequential access for serial and sequential files Direct access for sequential and random files

3. Show understanding of hashing algorithms

Notes and guidance

Describe and use different hashing algorithms to read from and write data to a random / sequential file

Candidates should be able to:

1. Describe the format of binary floating-point real numbers

Notes and guidance

1. Use two’s complement form

2. Understand of the effects of changing the allocation of bits to mantissa and exponent in a floating-point representation

2. Convert binary floating-point real numbers into denary and vice versa

3. Normalise floating-point numbers

Notes and guidance

Understand the reasons for normalisation

4. Show understanding of the consequences of a binary representation only being an approximation to the real number it represents (in certain cases)

Notes and guidance

Understand how underflow and overflow can occur

5. Show understanding that binary representations can give rise to rounding errors