Program Design (プログラム設計）

4. The process specification
（プロセス仕様）
You will learn:（次の内容を学び）
The concept of process specification（プロセス仕
様の概念）
Notations for process specification （プロセス仕
様記法）
4.1 What is process specification?
（プロセス仕様とは）
(1) The problem:（問題点）
Processes in a DFD are not defined in detail. Therefore, it
is almost impossible to understand the meaning of the
DFD precisely and accurately.（DFDでは、プロセスの機
能を定義していない）
(2) The definition of process specification:（プロセス仕様
の定義）
Description: a process specification is a document for the
process that specifies what to do in transforming its
inputs to outputs. （プロセス仕様とは、入力データフ
ローを出力データフローへの変換に何をするということ
を明確に定義する文書である）
(3) What kinds of processes need to be specified?（どんなプ
ロセスに仕様を書く必要があるか）
Only the lowest level processes that do not have
decompositions in a hierarchy of DFDs need to be
specified, because they have no definitions in the DFD
hierarchy at all.（階層的DFDのなかで分解されていない
プロセスだけに仕様を書く必要がある）
Processes that are decomposed into lower level DFDs do
not need to be specified, because they are actually defined
by their decompositions. （分解されたプロセスに対して、
分解されたDFDによるそのプロセスを定義されているの
で、仕様を書く必要がない）
For example, in the following DFD hierarchy, processes 2
and 3 do not need a specification, whereas processes 3.1,
2.2.1, 2.2.2, 2.2.3, and so on need to be defined.
b
a
T1
T2
The
System
c
T3
Figure 0 the context diagram
a
d
e
b
2
1
f
h
s
4
3
g
c
Figure 1 the decomposition of process The System
d
h
e
j
2.1
2.2
i
3.1
b
3.3
f
Figure 2
3.2
s
g
2.3
h
k
3.4
l
Figure 3
j
2.2.1
h
x
2.2.2
y
2.2.3
Figure 4
b
4.2 Notations for process specification
（プロセス仕様記法）
We introduce the following most commonly used
notations:（次の三つの仕様記法を紹介する）
Pre and post-condition notation（事前条件と事後
条件の記法）
Structured English（構造化英語）
Decision table（意思決定表）
4.2.1 Pre and post-condition notation
（事前条件と事後条件の記法）
The primary idea of writing process specification using pre and postcondition notation: （事前条件と事後条件の記法の基本的な考え
かた）
A process can be defined by giving a pre-condition and
post-condition. The pre-condition describes a constraint on
the input data flows before the execution of the process,
while the post-condition provides a constraint on the output
data flows after the execution. （プロセスの機能を事前条件
と事後条件により定義できる。事前条件は、プロセスの入
力に対しての制限であり、事後条件は、プロセスの出力に
対しての制限である）
Syntax for a process specification: this notation is a
simplified version of process specification notation
used in the SOFL specification language.（プロセス
仕様の文法。SOFL仕様言語のプロセス仕様記法を使う）
SOFL stands for Structured Object-oriented Formal
Language. （SOFLは、 Structured Object-oriented Formal
Languageと意味する）
process processName(input data flows) output data flows
ext stores
pre condition1
post condition2
end_process
For example, let’s take the three processes in the
following DFD as an example to show how the pre
and post-condition notation is used to define
processes:（次のDFDのプロセス仕様を考えよ）
expenses-file
7.2
total-exp
month
7.1
Provide Month
Find All
Related Items
7.3
items-list
Calculate Total
Expense
total-amount
process Provide-Month() month
pre true
post month = a month number obtained from the input
device.
end_process;
process Find-All-Related-Items(total-exp, month)
items-list
ext expenses-file
pre total-exp command is available and 1 <= month <= 12
post items-list = all of the items that are purchased within
the requested month, obtained from the expenses-file.
end_process;
process Calculate-Total-Expense(items-list)
total-amount
pre true
post total-amount = add up all of the prices for all
of the items recorded in items-list.
end_process;
4.2.2 Structured English
（構造化英語）
Structured English is English with structure. That is, it is
basically English, but there are restrictions on the
structure of sentences. The goal of applying such
restrictions is to achieve a reasonable balance between the
precision of formal programming languages and the
casual informality and readability of the English texts.
（構造化英語は、構造が明確である英語の表現である）
Structured English includes two kinds of sentences:（構造
化英語は、次の二つの語句を含む）
Basic sentences（基本語句）
Compound sentences（複合語句）
Basic sentences（基本語句）
A basic sentence may be one of the following three kinds:（基本語句
は、次の三つの種類の語句を含む）
An algebraic equation. （代数方程式）For example,
x = (y * z) / (q + 4)
a = b ** 2 + d/2
A simple imperative sentence consisting of a verb and object. There
is no restriction on verbs and objects. （動詞と目的語から形成され
た命令語句）For example,
Calculate total-amount
Input x
A mixture of the both. （以上の二種類の語句の組合せ）For
example,
Compute total-amount =
item1.price + itme2.price + item3.price
A list of verbs that are often used in Structured English:
（次の動詞は、構造化英語に良く使われる）
Get (or Accept or Read)
Put (or Display or Write)
Find (or Search or Locate)
Add
Subtract
Multiply
Divide
Compute
Delete
Validate
Move
Replace, Set, Sort
Compound sentences
(複合な語句）
A compound sentence is one of the following:（複合
な語句は、次の種類を含む）
Sequence of sentences（順序語句）
Block sentence（ブロック語句）
Conditional sentences（条件語句）
Multiple choice sentence（多数選択語句）
Iteration sentences（反復語句）
(1) Sequence of sentences （順序語句）
Syntax:（文法）
S1;
S2;
S3;
Example: a function to register an item data in the
expenses-file:（expenses-fileに一つのデー
タ項目を登録する構造化英語）
Get item-d;
Register item-d in expenses-file;
Add item-d.price to total-expense;
(2) Block sentence （ブロック語句）
Block sentence is used to group a sequence of sentences
into a single sentence.
Syntax:（文法）
begin
sentence-1;
sentence-2;
sentence-3
end;
Example,（例え）
begin
Get item-d;
Register item-d in expenses-file;
Add item-d.price to total-expense;
end;
(3) Conditional sentences （条件語句）
Conditional sentences include if-then and if-then-else
sentences:
Syntax:（文法）
if condition
then sentence;
end-if;
or
if condition
then sentence-1
else sentence-2
end-if;
Example:（例え）
(1)
if 1<= month <= 12
then Display items-d purchased in this month
end-if;
(2)
if 1<= month <= 12
then Display items-d purchased in this month
else Display warning message
end-if;
(4) Multiple choice sentence
（多数選択語句）
Syntax:（文法）
do case variable
value-1, value-2: sentence-1;
value-3, value-4: sentence-2;
……
value-9, value-10: sentence-10;
otherwise: sentence;
end-case;
Example: （例え）
do case input /* to the Personal Expenses
Management System */
item-reg:
Register item-d;
single-item-d: Display all of the items of this kind;
total-exp:
Output the total expense;
all-item-d: Display all of the items data in
expenses-file;
otherwise: Give warning message;
end-case;
(5) Iteration sentences （反復語句）
Iteration sentences include while-do and do-while sentences.
Syntax:（文法）
while condition do
sentence-1
end-while;
do
sentence-1
while condition
end-while;
In both while-do and do-while sentences, sentence-1 is executed
until the condition becomes false. The only difference between
them is that sentence-1 is firstly executed after evaluating the
condition as true in while-do sentence, whereas the first execution
of sentence-1 in do-while sentence is done before evaluating the
condition.
Examples:（例え）
while items-list <> empty do
begin
Get next item-d;
Display item-d
end
end-while;
do
begin
Read item-d;
Register item-d in expenses-file
end
while item-d.name <> “end”
end-while;
4.2.3 Decision table
Decision table describes that actions are taken based
on a combination of certain conditions or values.
Decision table is in particular effective in defining
processes that produce some output or take actions
based on complex conditions.
General format of a decision table:
Rules
Conditions or variables
Actions
Each column shows a rule, indicating what actions are
taken under what conditions.
Example of decision table
1
2
3
Presence >= 10
Y
Y
N
Exam-grade
C
B
D
Project-score >= 60
Get credit
Y
X
N
X
Get no credit
N = No
X = Take or perform
Y
A
Y
X
X
X
Recommend award
Y = Yes
Y
4
C = grade C
B = grade B
A = grade A
This decision table can be translated into the equivalent
Structured English:
if Presence >= 10 and Exam-grade = C and Project-grade >= 60
then Get credit
else if Presence >= 10 and Exam-grade = B and Project-grade < 60
then Get credit
else if Presence < 10 and Exam-grade = D and Project-grade >= 60
then Get no credit
else if Presence >= 10 and Exam-grade = A and Project-grade >= 60
then begin
Get credit;
Recommend award
end
end-if;
Advantages of decision table
The designer can concentrate on one rule at a time.
The decision table does not imply any particular
form of implementation. This will give the
programmer freedom in choosing most efficient
implementation strategy.
The decision table can be automatically
transformed into a program structure. However,
whether the program is executable or not depends
on if all of the involved conditions can be
evaluated and all of the actions can be executed
automatically.
Exercise 4
1. Write the process specifications for the processes
Receive-Request, Check-Password, Withdraw, and
Show-Balance given in Exercise 2.1, using the
following three notations, respectively.
(1) Pre and post-condition notation
(2) Structured English
(3) Decision table
2. Use structured English to describe the following decision
table.
1
work-hours >= 8
position
publication <= 5
2
Y
N
Y
P
P
P
RA
Y
N
Y
N
X
DECREASE bonus
GIVE award
N = No
X
X
X
P = Professor
RA = Research Assistant
X = Take or perform
4
Y
INCREASE bonus
Y = Yes
3
3. Translate the following Structured English expression into
a decision table.
if x > 5 and y > x + 1 and z > x + y
then
begin
Compute sum = x + y + z;
Output sum;
end
else
begin
Compute sum = x * y * z;
Output sum;
end;
Small project 1.3
Use Structured English to write process
specifications for all the three processes involved
in the hierarchical DFDs resulted from small
project 1.1.

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