Data and processes in computing: 4 Processes

4 Processes

Processes that can be applied to data

Having looked at some forms of data, we now turn our attention to processes that can be applied to data. Each process that we consider in this section will input data of a specified form, and will result in a corresponding value. For example, one process, which we will call ASC, takes a character as input, and has as its resulting value the integer giving the ASCII code of the input character (as listed in Table 2). Another process, which we will call SIZE, takes a sequence as input, and has as its resulting value the length of the sequence (which will be an integer).
It is important to distinguish between a description of the outcome required when a process is applied to a form of data, and a description of the exact steps to be taken to achieve the desired outcome. Here, we are concerned only with the first of these; that is, with providing an overview of a computing process. You might like to think of this as a “black box” view of the process. We do not, at this stage, care how one obtains the output value.

Data and processes in computing: Objectives for Section 3

Objectives for Section 3

After studying this section you should be able to do the following.

· Recognise and use the terminology: disjoint union; power set (of a set); representation (of a data abstraction).

· Use and interpret the notation:

o  X Y for the disjoint union of the sets X and Y ;

o  SeqOfSetOfInt for the set consisting of all sequences whose members are sets of integers (and similar notations).

Exercises on Section 3

Exercise 7

Each of (a)–(c) is a member of one of the sets given in (i)–(iii). Say which item comes from which set.
Sets: (i) SetOfSeqOfChar. (ii) SeqOfSetOfChar. (iii) SeqOfSeqOfChar.
(a) {“error1”, “error2”, “error3”}.
(b) [“error1”, “error2”, “error3”].
(c) [{‘e’,‘1’}, {‘T’}, {‘q’,‘w’,‘e’,‘r’,‘t’,‘y’}].

Answer