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Lecture 12 – Process Specification

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  1. Lecture 12 – Process Specification Maria Petridou Definition, Motivation and Elements Structured English Decision Tables Decision trees

  2. Definition, Motivation and Elements • 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 Maria Petridou

  3. Definition, Motivation and Elements • 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 Maria Petridou

  4. Definition, Motivation and Elements • 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. Maria Petridou

  5. Definition, Motivation and Elements • 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. Maria Petridou

  6. Structured English • 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. Maria Petridou

  7. Structured English • Sequences AverageCost = Total / Items Fine = AverageCost x 0.15 Print “Fine to pay:” Fine • Cases CASE IF day is 5 THEN print “Saturday” IF day is 6 THEN print “Sunday” ELSE print “Weekday” Maria Petridou

  8. Structured English • Decisions IF price less than credit THEN print “You have credit” ELSE print “You have no credit” • Iterations DO 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 Maria Petridou

  9. Decision Tables • 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. Maria Petridou

  10. Decision Tables • 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. Maria Petridou

  11. Decision Tables Identify the conditions, rules and actions. Number of rules: 2 ^ No of Conditions. Maria Petridou

  12. Decision Tables Construct the table Maria Petridou

  13. Decision Tables Then combine the rules – Optimised Table Maria Petridou

  14. Decision Trees • 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. Maria Petridou

  15. Decision Trees • Compared to decision tables, decision trees are more readily understood by others in the organization. Action 2 Condition 3 4 Action 1 Condition 1 2 3 Maria Petridou 1 5 Condition 4 Action 3 6 Condition 2 Action 4

  16. Decision Trees • Example. Decision tree for the decision-making logic in library system. Maria Petridou Reading: (Kendall&Kendall, chapter 9).