Page 55 - DCAP305_PRINCIPLES_OF_SOFTWARE_ENGINEERING

Unit 3: Software Requirements

Multi-instruction, Multi-data machines (MIMD) Notes
These machines can fetch several instructions and objects in parallel. They can also do arithmetic
and logical operations simultaneously on different data objects. The decision of how to sequence
them depends on the compiler.

Data Dictionary
This is another tool of requirement analysis which reduces complexity of DFD. A data dictionary
is a catalogue of all elements of a system. DFD depicts flow of data whereas data dictionary
gives details of that information like attribute, type of attribute, size, names of related data
items, range of values, data structure definitions etc. The name specifies the name of attribute
whose value is collected. For example, fee deposit may be named as FD and course opted may
be named as CO.
Related data items captures details of related attributes. Range of values store total possible
values of that data. Data structure definition captures the physical structure of data items.
Some of the symbols used in data dictionary are given:
X= [a/b] x consists of either data element a or b
X=a x consists of an optional data element a
X=a+b x consists of data element a and b
X=y{a}z x consists of some occurrences of data elements at which are
between y and z.
Separator
Comments
@ Identifier
( ) Options

The data dictionary of payroll may include the following fields:
PAYROLL = [Payroll Details]
= @ employee name + employee + id number + employee address + Basic
Salary + additional allowances
Employee name = * name of employee *
Employee id number = * Unique identification no. given to every employee*
Basic Salary = * Basic pay of employee *
Additional allowances = * the other perks on Basic pay *
Employee name = First name + Last name
Employee address = Address 1 + Address 2 + Address 3

Structured Requirements Definition
Structured Requirements definition is an approach to perform the study about the complete
system and its various sub-systems, the external inputs and outputs, functionality of complete
system and its various sub-systems. The following are various steps of it:
Step 1 : Make a user level data flow diagram.
This step is meant for gathering requirements with the interaction of employee. In
this process, the requirements engineer interviews each individual of organisation in
order to learn what each individual gets as input and produces as output. With this
gathered data, create separate data flow diagram for every user.

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