And Franchise Colleges
10 THE DATA DICTIONARY
: Process Descriptors
By MANSHA NAWAZ
Section 10
Data Dictionary - Process
Descriptors
1
Process Descriptors
• Aim
– to be able to construct an internal process
mini-spec using structured english
• Objectives
– to identify the necessary sequence of actions
– to identify any optional paths of action
– to identify any possible iterative actions
– to record using given syntax
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Data Dictionary - Process
Descriptors
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Lecture Outline
•
•
•
•
•
Process descriptors in a data dictionary
internal process mini-specs
vocabulary of structured english
sequence, selection & iteration
local variables
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Data Dictionary - Process
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NOTE
• Programmers
– you will have awareness of structured english
• Non-Programmers
– descriptions are sufficient
• Also consideration
–
–
–
–
storyboards
screen design
bullet point description
address what needs to be done for the process
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Data Dictionary - Process
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Data Dictionary – Process Descriptors
• The connection between the DFD and DD for
processes is as follows:
– we record a Process Specification for each process
on the DFD that isn’t exploded.
• English is very ambiguous and would lead to
long-winded and unclear process specifications.
• We want something clearer and more concise.
• Structured English is widely used in structured
methods.
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Data Dictionary - Process
Descriptors
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Process Descriptors
• Show how something is to be done within a process
• Techniques covered is based the below form
• Mini Spec is where we describe the action in terms of an algorithm or
structured english
• Structured English revolving around sequence, selection & iteration
instructions
DATA DICTIONARY: PROCESS DESCRIPTORS
Name:
Description:
Data Inputs:
Data Outputs:
Variables:
Mini-Spec:
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Data Dictionary - Process
Descriptors
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Mini Spec - Structured English
• Mini Spec or Process Specification is a form of English with
a limited number of constructs and a limited vocabulary.
• Most programs, like data structures, are made up of:
• Sequence
• Selection
• Iteration
do the following in this order
do this or that depending on...
keep doing this until...
• Within the Mini-Spec or process specifications we will use:
•
•
•
•
•
•
Imperative verbs, like multiply, print, add, create or update
Data dictionary terms member, book.author, order
reserved words IF...THEN, READ
Mathematical symbols
Labels
A little English or text for readability
• According to convention, data dictionary terms are underlined and
construct words are written in CAPITALS.
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Data Dictionary - Process
Descriptors
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Problems with English Text
• ambiguous
– x and (y or z) OR
– (x and y) or z?
• vague
– what is a good
payment history?
• too long
“customers who place
more than £10,000 of
orders per year and
have a good payment
history or have been
with us more than 20
yrs are to receive
10% discount on all
orders”
Solution – Use Structured English Text
Sequence - Selection - Iteration
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Data Dictionary - Process
Descriptors
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Sequence
A series of imperative statements, for example:
Calculate-Discount
Get price given item-no
Multiply quantity by price giving gross
Multiply gross by 0.1 giving discount
Invoice-total = gross – discount
price, item-no, quantity, gross, discount and invoice-total are all DD
terms, whose meanings have already been defined.
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Data Dictionary - Process
Descriptors
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Sequence cont..
• Process specifications are often written in a hierarchical,
top-down fashion, like the way sets of DFDs are
developed by explosion.
• To this end, DO followed by a label is used to carry out a
block of statements at a lower level.
…. ….
….
….
….
….
DO Calculate-Invoice-Total
…. ….
….
….
….
….
Calculate-Invoice-Total
Get price given item-no
Multiply quantity by price giving gross
DO Calculate-Discount
Invoice-total = gross – discount
….
….
….
….
….
….
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Data Dictionary - Process
Descriptors
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Sequence Example
• Given the top-level statement DO Stir-Fry-Meal
and using Structured English, write two DO
statements to specify the process Stir-Fry-Meal,
which consists of 2 parts, one to select the main
ingredient and one to cook the dish.
Answer
Stir-Fry-Meal
DO Select-Main-Ingredient
DO Cook-Dish
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Data Dictionary - Process
Descriptors
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Selection
• used when more than one possible action
IF condition1
reserved word
action1
indentation
ELSE (condition2)
not condition in ()
action2
indentation
ENDIF
end the selection
• also use ELSEIF or CASE
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Data Dictionary - Process
Descriptors
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Selection cont…
• This shows alternatives and uses the construct words IF,
ELSE and ENDIF.
IF delivery is local
Add £5 to invoice-total
ELSE (delivery not local)
Add £20 to invoice-total
ENDIF
• Note how indentation is used to help the meaning.
• Also, note how the reverse of the original condition is
stated for the ELSE part for clarity.
• Whilst optional, this is good practice.
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Data Dictionary - Process
Descriptors
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Selection – IF
• Using Structured English write an IF … ELSE …
ENDIF statement to specify the process SelectMain-Ingredient.
If a guest is a meat eater, the main ingredient will be
chicken. Otherwise the main ingredient will be
vegetables.
DD terms already defined are Guest, Carnivore and Main-Ingredient.
Answer
Select-Main-Ingredient
IF Guest is Carnivore
Main-Ingredient = ‘Chicken’
ELSE
Main-Ingredient = ‘Vegetables’
ENDIF
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Data Dictionary - Process
Descriptors
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Selection – Nested IF
We can nest IF constructs, for example:
IF delivery is local
IF Order-value > £50
Add £1 to Invoice-Total
ELSE
Add £5 to Invoice-Total
ENDIF
ELSE
Add £20 to Invoice-Total
ENDIF
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Data Dictionary - Process
Descriptors
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Selection – Case
Rather than use a series of IF constructs we
can use the CASE .construct for clarity:
IF constructs:
IF X = 1
Add B to A
ENDIF
IF X = 2
Add C to A
ELSE
Add D to A
ENDIF
Section 10
Case constructs:
DO CASE
CASE X = 1
Add B to A
CASE X = 2
Add C to A
OTHERWISE
Add D to A
ENDCASE
Data Dictionary - Process
Descriptors
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Iteration
• This is used for loops or repetitions
– when action to be carried
– Repeat Until or Do While
REPEAT
statement1
...
UNTIL condition
reserved word
indentation
end condition
example
REPEAT
DO Calculate-Invoice-Total
Print Invoice
UNTIL no more Sales-Details
Section 10
DOWHILE condition
reserved word
statement1
indentation
...
ENDDO
end condition
example
DOWHILE more Sales-Details
DO Calculate-Invoice-Total
Print Invoice
ENDDO
Data Dictionary - Process
Descriptors
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Iteration Example
• Using Structured English specify the process Cook-Dish.
• You need a sequence for adding oil to the wok, heating
the oil, then adding the ingredients, followed by an
iteration while you stir fry the ingredients until they’re
cooked.
• DD terms already defined are Oil, Wok and Cooked.
Answer
Cook-Dish
Add Oil to Wok
Heat Oil
Add Ingredients to Wok
DO WHILE Ingredients NOT Cooked
Heat Oil
Cook Ingredients
ENDDO
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Data Dictionary - Process
Descriptors
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Local Variables
• sometimes a local variable is used
– placeholder for a value & make clearer
• defined within the process specification
SET subtot = 0
REPEAT
Add (qty*unitprice) to subtot
UNTIL no more orderitems
SET total = subtot
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Data Dictionary - Process
Descriptors
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Complete Structured English
DO Stir-Fry-Meal
Stir-Fry-Meal
DO Select-Main-Ingredient
DO Cook-Dish
Select-Main-Ingredient
DO CASE
CASE Guest is Carnivore
:
Main-Ingredient = ‘Chicken’
CASE Guest is Fish-Eater
Main-Ingredient = ‘Prawns’
OTHERWISE
Main-Ingredient = ‘Vegetables’
END CASE
Cook-Dish
Add Oil to Wok
Heat Oil
Add Ingredients to Wok
DO WHILE Ingredients NOT Cooked
Heat Oil
Cook Ingredients
ENDDO
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Data Dictionary - Process
Descriptors
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Document : Design Specification
– Data Dictionary
•
•
•
•
Data Stores - Structures & Elements
Data Flow - Structures & Elements
Data Stores and Flow Usage
Process Descriptions
– NORMALISATION
lecture 08
lecture 08
lecture 08
lecture 09
lecture 10
lecture 11
• Database Tables derived from Data Store
Descriptions
Section 10
Data Dictionary - Process
Descriptors
21
Document : Data Dictionary
– Data Dictionary
•
•
•
•
Data Stores - Structures & Elements
Data Flow - Structures & Elements
Data Stores and Flow Usage
Process Descriptions
lecture 08
lecture 08
lecture 08
lecture 09
lecture 10
– For each process list
» Process Usage & Mini Spec
» Process Screen Shot
Section 10
Data Dictionary - Process
Descriptors
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Summary
• Process specifications are formed by combining sequence,
selection and iteration constructs.
–
–
–
–
DO is used to structure the specification, using labels.
Construct words are written in CAPITALS.
Data dictionary terms are underlined.
Imperative verbs are used, plus a little English for readability and
some mathematical notation.
– Process specifications are not at the detailed program coding level.
• Structured English is recommended as a process
specification tool because:
– It uses standard constructs and rules, making it clear and concise.
– It uses data dictionary terms, making it precise.
– To remove ambiguity, it uses nesting and the normal computer rules
of precedence, ie ANDs are evaluated before ORs.
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Data Dictionary - Process
Descriptors
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Further Reading
• Notes from Annette Marshall on Data Dictionary
• http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk6.doc
• http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk6a.doc
• http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk7.doc
• http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk7a.doc
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Data Dictionary - Process
Descriptors
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