Transcript technical methods

Technical Methods for
Specifying
Requirements
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When to Use Technical
Methods
 If the description of the requirement is too
complex for natural language and if you
cannot afford to have the specification
misunderstood, you should consider
writing or augmenting that portion of the
requirements set with a “technical
methods” approach.
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Examples of Technical Methods
 Pseudocode
 Finite state machines
 Decision tables and decision trees
 Activity diagrams (flowcharts)
 Entity-relationship models
 And many more
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Pseudocode
 Imperative sentences with a single verb and a
single object.
 A limited set, typically not more that 40-50, of
“action-oriented” verbs from which the
sentences must be constructed.
 Decisions represented with a formal IF-ELSEENDIF structure.
 Iterative activities represented with DO-WHILE
or FOR-NEXT structures.
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Pseudocode Example
The algorithm for calculating deferred-service revenue
earned for any month is:
Set Sum(x)=0
FOR each customer x
IF customer purchased paid support
AND (Current month) >= (2 months after ship date))
AND (Current month) <= (14 months after ship date))
THEN Sum(x)=Sum(x) + (amount customer paid)/12
END
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Finite State Machines
 Sometimes it is convenient to regard the system
as a hypothetical machine that can be in only one
of a given number of states at any specific time.
 In response to an input (from the user or an
external source) the machine changes state and
carries out some action and/or generates an
output.
 Both the output and the next state can be
determined solely based on understanding the
current state and the event that caused the
transition.
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Example of a State Transition
Diagram
Light burned out
Even Lit
Even Lit/ LOUT
Off
Off
On
Count
OFF
Count
1 sec
Off
1 sec
Off
Odd Lit
Odd Lit/ LOUT
Light burned out
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Example of a State Transition
Matrix
Event
State
On
Press
Off
Press
Count
Press
Bulb
Burns
Out
Every
Second
Output
Off
Even lit
---
---
---
---
Both
Off
Even lit
---
Off
Odd lit
LO/
Even lit
---
Even lit
Odd lit
---
Off
Even lit
LO/
Odd lit
---
Odd lit
Light out/ --Even lit
Off
---
Off
LO/
Odd lit
Even lit
Light out/ --Odd lit
Off
---
Off
LO/
Even lit
Odd lit
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Decision Tables and Decision
Trees
 When a requirement deals with a
combination of inputs and different
combinations of those inputs lead to
different behaviors or outputs, decision
tables or decision trees can be helpful.
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Activity Diagrams
 Flowcharts and UML Activity Diagrams
are understandable by most people.
 They present the same information that
can be given in pseudo code, but they
show it visually.
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Entity-Relationship Diagrams
 They are useful for showing the
relationships among data within the
system.
 ERDs focus on the external behaviors of
the system.
 They can be difficult for nontechnical
readers to understand.
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