l ecture 12 – p rocess s pecification definition, motivation and elements structured english...
TRANSCRIPT
LECTURE 12 – PROCESS SPECIFICATION
• Definition, Motivation and Elements• Structured English• Decision Tables• Decision trees
Software Project Management Maria Petridou
1
DEFINITION, MOTIVATION AND ELEMENTS
Software Project Management
2
Maria Petridou
Process specification methods are tools to describe, analyse and document the decision-making logic in processes.
Process specification can be to describe low-level or high-level processes.
Process specification is required for describing in detail the way in which processes transform the input into output.
Process specification helps to achieve: Completeness Accuracy Efficient communication
DEFINITION, MOTIVATION AND ELEMENTS
Software Project Management
3
Maria Petridou
Goals of process specification: Describe process accurately -Specify what will happen in the
process given all possible conditions Validate the system design - There should be consistency
between DFDs, ERDs and process specifications Help when processes require specification
DEFINITION, MOTIVATION AND ELEMENTS
Software Project Management
4
Maria Petridou
Information that should be included in a complete process specification: Process name and ID Brief verbal description List of input and output data flows Type of process - batch, online or manual Description of the process decision-making logic Other information such as use of pre-written code, clarifications,
incomplete decisions, etc.
DEFINITION, MOTIVATION AND ELEMENTS
Software Project Management
5
Maria Petridou
Methods to specify the process decision-making logic: Structured English - Based on written instructions and statements.
Similar to pseudo-code. Decision Tables – Based on conditions, rules and actions. Similar
to truth tables. Decision Trees – Based on graphical illustration of the sequential
decision process. Similar to flow diagrams.
STRUCTURED ENGLISH
Software Project Management
6
Maria Petridou
Used for simple decisions making logic Use capitalised keywords: IF,THEN,WHILE, etc. Careful use or some logical and relational words such as:
and, or, greater than, etc. Based on four types of logic: sequences, decisions, cases and
iterations.
STRUCTURED ENGLISH
Software Project Management
7
Maria Petridou
SequencesAverageCost = Total / Items
Fine = AverageCost x 0.15
Print “Fine to pay:” Fine
CasesCASE
IF day is 5
THEN print “Saturday”
IF day is 6
THEN print “Sunday”
ELSE print “Weekday”
STRUCTURED ENGLISH
Software Project Management
8
Maria Petridou
Decisions
IF price less than credit
THEN print “You have credit”
ELSE print “You have no credit”
IterationsDO
Print “Enter password”
Get Pswd
WHILE Pswd ≠ ActivePswd
i=1
DO WHILE i < 10
j = i x i
i = i +1
print (i,j)
END DO
DECISION TABLES
Software Project Management
9
Maria Petridou
Used for more complex decision-making logic. Use conditions, rules and actions arranged in a table to express decision
making logic. Determine adequate number of conditions. Eliminate redundancy by combining rules (condition alternatives +
actions). Re-arrange the table if required to achieve clarity. Four main problems that can occur in developing decision tables:
incompleteness, impossible situations, contradictions, redundancy.
DECISION TABLES
Software Project Management
10
Maria Petridou
Example. When you go to the bar, may want 4 cokes, 4 pints and you may want 4 whiskies. You may of course want nothing! After 4 pints you will be drunk, after 4 whiskies you will be very drunk and if you combine whiskies and pints then you will be mullered!Produce an optimised decision table to show how drunk you might get depending on the decisions you make.
DECISION TABLES
Software Project Management
11
Maria Petridou
Identify the conditions, rules and actions.Number of rules: 2 ^ No of Conditions.
DECISION TABLES
Software Project Management
12
Maria Petridou
Construct the table
DECISION TABLES
Software Project Management
13
Maria Petridou
Then combine the rules – Optimised Table
DECISION TREES
Software Project Management
14
Maria Petridou
Used for complex decision-making logic and in particular, to maintain the sequence of decisions.
Use conditions (circles) and actions (squares) in a branching tree to express decision-making logic.
Determine conditions, actions and their sequence. List all required possibilities when drawing the tree. Construct the tree from left to right. The order of checking conditions and executing actions is immediately
noticeable in decision trees.
DECISION TREES
Software Project Management
15
Maria Petridou
Compared to decision tables, decision trees are more readily understood by others in the organization.
1
2
6
Condition 1
Condition 2Action 4
Action 13
4
5
Condition 3
Condition 4Action 3
Action 2
DECISION TREES
Software Project Management
16
Maria Petridou
Example. Decision tree for the decision-making logic in library system.
Reading: (Kendall&Kendall, chapter 9).