Code Design

1
Code Design

• (The use of pseudo code
• for process descriptors)

2
What are mini specifications?

• A process descriptor
• provides a detailed explanation of the internal
  processing policy of a functional primitive that
  transforms input data into output data

3
Documenting a process

• Various means and tools include
• pseudo code (structured English)
• decision trees
• decision tables
• action diagrams
• mathematical algorithms

4
Documenting the policy

• Need only specify the processing policies
  necessary to transform data or simply provide
  data.
• When stating policy, only specify what rather
  than how with regard to processing data.
• Try to specify data transformations from the
  users vantage point.

5
A process descriptor...

• must exist for every functional primitive in a
  DFD
• must state the ways in which data flowing into
  the process are transformed into output flows
• must state the policy that governs the
  transformation, not the method to do so
• should seek to control redundancy
• should use a small set of constructs

6
Additional process descriptor information

• As well as logic the process descriptor should
  mention
• processor requirements
• security requirements
• time requirements
• processing requirements
• performance requirements
• safety requirements

7
Specifying logic (1)

• Sequence
• Repetition

Do While
Repeat Until
8
Specifying logic (2)

• Selection

A
IF
IF THEN ELSE
CASE
9
Pseudo code/structured English

• Programming Design Language (PDL) by Caine and
  Gordon, a pidgin language that
• uses the vocabulary of one language (i.e.
  English) and the overall syntax of another (i.e.
  a structured programming language)
• Tom DeMarco defines structured English as
• a specification language that uses a limited
  vocabulary and a limited syntax

10
Structured English vocabulary

• The vocabulary consists of
• imperative English-language verbs
• terms defined in the data dictionary
• certain reserved words for logic formulation
• The structured English minimal set can now be
  defined

11
Syntax and variables

• Data flows, data stores, common processing
  routines upper case hyphenated words (define in
  data dictionary)
• Local variables upper case hyphenated words (do
  not define in data dictionary)
• Commands, primitive functions, sources/sinks
  lower case first letter capitalised
• Prepositions/verbs lower case

12
Assignment statements

• Assign values to single variables with
• VARIABLE Value / Literal / Expression
• VARIABLE Value / Literal / Expression
• Set VARIABLE to Value / Literal / Expression
• Compute VARIABLE Expression

13
Operators (1)

• Arithmetic expressions
• Results are numeric
• Operators are addition ()
• subtraction (-)
• multiplication ()
• division (/)
• exponentiation ()

14
Operators (2)

• Boolean expressions
• Results are either True or False
• Logical operators And, Or and Not
• Relational operators less than (lt)
• less than or equal (lt)
• equal ()
• not equal (lt gt)
• greater than (gt)
• greater than or equal (gt)

15
Sequence of execution

• All commands are intended to be executed in a
  forward sequential order as written unless the
  logic or command indicates otherwise.
• It is helpful to establish
• indentation rules to help
• identify computational
• units.

16
Repetition statements (1)

• Do While statement
• While condition Do
• statements
• EndWhile

False
True
17
Repetition statements (2)

• Repeat Until statement
• Repeat
• statements
• Until condition

statements
condition
True
False
18
Decision statements

• If...Then...Else
• If condition then
• statements1
• else
• statements2
• endif

condition
True
False
statements1
statements2
19
Input/output statements

• Various ways of designating flow of data into and
  out of a functional primitive process are
  acceptable
• Input Output
• Accept Send
• Get Put
• Read Write or Print

20
File manipulation

• These commands not absolutely necessary
• Create data-entry in data-store-name
• Delete data-entry from data-store-name
• Search data-store-name for condition
• Locate data-element(s) in data-store-name for
  condition
• Match data-element-1 to data-element-2 in
  data-store-name
• Merge data-store-name-1 into data-store-name-2

21
Case statements

• Allows several alternative sets of processing
  logic to be distinguished without the need for
  multiple If..Then..Else statements

• Case 1 (condition)
• statements1
• Endcase 1
• Case 2 (condition)
• statements2
• Endcase 2
• Else statements (n1)
• Endcases

22
Common processing routines (1)

• Defined in the data dictionary
• Can be called more than once in the system
• CALL statement lists the parameters needed by the
  called process to perform its tasks.
• The calling process receives the output data
  elements from the called routine
• CALL common-processing-routine-name (parameter
  list)

23
Common processing routines (2)
Exchange request
Currency details
Total currency
Converted currency
Currency Type
Exchange Rate
Determine current exchange rate
24
Common processing routines (2)

• Calculate Currency Exchange descriptor 7.1.2
• Input Currency details from Validate currency
  exchange
• Call Determine current exchange rate
• (Currency Type, Exchange Rate)
• Multiply Currency Value by Exchange Rate
• Output Total currency to Calculate commission fee
• Stop

25
Suspension, termination comments

• It may be necessary at times to halt processing
  temporarily
• to allow a passage of time
• Output Request-For-Info-Msg to Customer
• WAIT
• Input Customer-Info from Customer
• to wait to be reactivated by another process
• Output Customer-Rec to Master-File
• WAIT