5. Control-flow design representations制御の流れの設計表現

The structure chart （構造図）The Jackson Structure Diagram （ Jackson 構造図）The flowchart （フローチャート ）The Nassi-Shneiderman diagram （ Nassi-Shneiderman 図）The Production Rule Notation (PRN) （生産規則記号）The Java-based pseudocode （ Java の擬似コード）

5.1 The structure chart （構造図）

The structure chart is a tree-like structure diagram that supports the top-down design. The structure chart uses the following three components ：（構造図は、木のような形で、 top-down 設計を支える。構造図は、次の三つの分品を使う）

The box is used to represent a function or procedure. （箱は機能又は操作を表す）The arc between a high level procedure and a low level procedure denotes a procedure invocation. （弧は操作の呼び出すを表す）The side-arrows represent data flows in terms of parameter-passing. The side-arrows are optional to use, depending on how detailed information about the system needs to be shown on the chart.（側面の矢印はデータの流れを現す）

The graphical representation

Procedure A invokes B, C, and D （操作 A は操作 B,C,D を呼び出す） ; procedure B invokes B1 and B2;procedure C invokes C1; and procedure D invokes D1 and D2.

A

B C D

B1 B2 C1

D1 D2

a1

a2 a3

a4

a5

a6

a7

a8

Example of a structure chart without side-arrows（側面の矢印を持っていない構造図）

Personal ExpensesManagement System

Take InputCommand

Register Items Display Single Item Display All Items Calculate Total

Input Item Data Register ItemOutput

ConfirmationMessage

Obtain All ItemsData

Make Item Table

Example of a structure chart with side-arrows（側面の矢印を持っている構造図）

Personal ExpensesManagement System

Take InputCommand

Register Items Display Single Item Display All Items Calculate Total

Input Item Data Register ItemOutput

ConfirmationMessage

Obtain All ItemsData

Make Item Table

command total-amount

all- items- list

items- table

Important points about the structure chart （構造図についての重要点）

The structure chart usually supports top-down design, but it does not necessarily mean it cannot support bottom-up design. （構造図は一般に top-down 設計を支えるが、 bottom-up 設計を支えない訳ない）The decomposition of a high level procedure is a collection of lower level procedures that are invoked by the high level process during its execution. （高いレベルの操作を分解した結果は、呼び出される低いレベルの操作の集合である）There is no indication of the order of invoking low level procedures by a high level procedure. （構造図は低いレベルの操作を呼び出す順番を示していない）It is usually difficult to draw many side-arrows, and therefore very inconvenient in modeling complex invocations of low level procedures. （側面の矢印が多くと、構造図は複雑になってしまう。そのため、複雑な設計には、側面の矢印を持つ構造図の構築は難しい）

5.2 The Jackson Structure Diagram （ Jackson 構造図）

The Jackson Structure Diagram is a notation used in JSP (Jackson Structured Programming), which was invented by Michael Jackson. （ Jackson 構造図は、Michael 　 Jackson に発明され、 JSP に使われる表現である）

This diagram is similar to the structure chart, but has additional expressive power: it also describes the sequence, selection, and iteration of procedure invocations. （ Jackson 構造図は、構造図に似てい

るが、もっとアルゴリズムらしい表現である）

The basic forms of Jackson Structure Diagram:（基本表現：）

Task1

Task2 Task3 Task4

SequenceThis diagram denotes that Task1 is implemented by the sequence

construct written in Structured English: Task2; Task3; Task4;

（この図は、 Task1 の機能が、 Task2 、 Task3,Task4 の順次的な実行として定義することを表す）

Task1

Task2 Task3

Selection

This diagram represents that Task1 is implemented by the choice construct given in Structured English: if C /*C is added during the translation */ then Task2 else Task3 end-if

（この図は、 Task1 の機能が、 Task2 と Task3 から構成された選択構造として定義することを表す）

Task1

Task2*

IterationThis diagram describes that Task1 is implemented by the iteration construct in Structured English: 　

　　 while C do /*C is added during the translation*/

Task2;

Update control variable;

end-while

（この図は、 Task1 が Task2 から構成された反復構造として定義することを表す。）

ExampleRegisterItems

RegisterOne Item

RegisterItem Name

RegisterItem Price

RegisterItem Shop

RegisterItem Date

RegisterAs Food

RegisterAs Others

*

5.3 The Flowchart 　（

The flowchart is a graphical notation that describes control flows among functions, possibly under certain conditions.

The flowchart is more suitable for detailed design, since rather detailed information of an algorithm is usually provided, such as conditions and the order of executions of functions.

However, the Hierarchical Flowchart can also be used for abstract design.

The basic components of the flowchartcondition

(c) arrow

(b) Rectangle

(a) Diamond

Task

Diamond denotes a condition; rectangle denotes a function; and arrow represents a control flow.

The basic forms of the flowchart

C

task1 task2

yes notask1

task2

C

task1

yes no

Sequence Choice Iteration

C

Task1 Task2 Task8

Multiple selection

v1 v2 v8

Exampletotal = 0;

foodTotal = 0;clothTotal = 0;othersTotal = 0;

End of expenses-file?

Read item

is-Food(item)?yes no

no yes

is-Cloth(item)?foodTotal += item.price

clothTotal += item.price othersTotal += item.price

Make the next item ready

Output foodTotal;Output clothTotal;Output othersTotal;

Output total

yes no

Hierarchical flowcharts

Hierarchical flowcharts are built by decomposing high level functions into lower level flowcharts.

Let us first look at an abstract description of a hierarchical flowcharts, and then look at a specific example.

c1

1

2

c2

3

(a) the top level flowchart

1.1

c3

1.2

yes

no

yes no

yes

no

c4

3.1

3.2 3.3

(b) the decomposition of task 1 (c) the decomposition of task 3

yes no

Obtain all items purchasedat the given shop from the

expenses-file

Calculate the total cost ofthese items

(a) the top level flowchart

1

2

yes

no

item.shop =the given shop?

End ofexpenses-file?

Put the item onthe item list

yes

no

(b) the decomposition of task 1

1.2

End of theitem list?

total +=item.price

2.2

no

yes

(c) the decomposition of task 2

Get thenext item

1.1Get next itemfrom the list

2.1

5.4 The Nassi-Shneiderman diagram (N-S diagram)（ N-S 図）

The N-S diagram is similar to the flowchart, but doesn’t use arrows. （ N-S 図は、フローチャートに似ているが、制御の流れを表現する矢印を使わない）

The motivations of inventing N-S diagram: （ N-S 図を開発した動機）

Enforce the use of only single-entry and single-exit constructs to ensure that designed programs are all structured programs. （一つの入り口と出口を持つプログラム構造のみを使わせることにより、構造化プログラムを作成することを保証する）Use graphical notation with less space than the flowchart. （少ない紙面を占める図を使うことにより、設計の紙面を節約する）

5.4.1 The basic components of the N-S diagram

Task1

Task2

Task3

if conditionif condition

case ofwhile condition

T FT F

Task1No

taskTask1 Task2

value1 value2 value3

Task1 Task2 Task3 Task1

Sequence if- then choice if- then-else choice

Mulitiple selection Iteration (while-do)

e

Example （事例）total = 0;

foodTotal = 0;clothTotal = 0;othersTotal = 0;

while not end of expenses-file

Read item

is-Food(item)T F

foodTotal += item.price

is-Cloth(item)T F

othersTotal +=item.price

Make the next item ready

Output total;Output foodTotal;Output clothTotal;Output othersTotal

clothTotal += item.price

5.5 The Production Rule Notation (PRN)

（生産規則記号 PRN ）PRN is a textual notation for program design, with the following

features: （ PRN は、次の特徴を持つテキスト言語である）It offers an effective mechanism for defining operations in a top-down manner. （トップドン設計を支え、操作を定義する有効な仕組みを提供している）It is suitable for both abstract and detailed design. （ PRN は、抽象設計と詳細設計に使用できる）It uses much less space than the graphical notations, such as the Structure chart, Jackson Structure Diagram, Flowchart, and N-S Diagram. （図の言語と比べて、設計紙面を大幅に節約する）It can be easily transformed into code (program written in a specific programming language). （コードへ変換しやすい）

5.5.1 The representation of an operation （操作の表現）

The fundamental concept in PRN is operation. An operation has the following possible forms: （ PRN の基本要素は、「操作」という。操作は次の四つの形式を取れる）

<OP> /*operation without input and output （入力とし出力がない操作） */[I1, I2, …, In]<OP> /*input-only operation （入力のみを持つ操作） */<OP>[O1, O2, …, Om] /*output-only operation （出力のみを持つ操作） */[I1, I2, …, In]<OP>[O1, O2, …, Om]

/*operation with both input and output （入力と出力を持つ操作 */

Example( 事例）

(1) <Check Errors>

(2) [item-name]<Find All Items>[items-list]

(3) [book-title, price]<Input>

(4) <Display Totals>[foodTotal, clothTotal, othersTotal>

5.5.2 The definition of operation( 操作の定義）

An operation OP is defined in the form: （操作を次の形で定義する）

OP ---> Statement end-op

The Statement has two types: basic and compound statements （二つの種類の Statement がある。基本と複合 Statement である）

The basic statements（基本 Statements)

Operation /*this means to call or invoke an operation （操作の呼び出し） */ Example: [item-name]<Find All Items>[items-list]

<V := E> /*assignment statement （代入文） */<Read>[O1, O2, …, Om] /*read from outside the

program system. （プログラムインタフェースから読み込む） */ [I1, I2, …, In]<Write> /*Write to the output

device （出力デバイスへ書き込む）*/

The compound statements （複合文） S1 ; S2 /*Sequence of statements*/

S1 |C /* if-then statement: if condition C is true, statement S1 is executed. Otherwise, S1 is not executed.*/

S1 |C S2 /* if-then-else statement: if C is true, S1 is executed; otherwise, S2 is executed. */

case expression of v1: S1; v2: S2; … vn: Sn end-case

{S1}C /*while-do statement: while C is true, S1 is repeatedly executed until C becomes false. */

begin S1 end /*block statement: equivalent to the compound statement S1. */

Example of operation definition（操作の定義の事例）

[expenses-file, shop-name]<Calculate the total cost of all items purchased at the given shop>[total]

--->

[expenses-file, shop-name]<Obtain all

items purchased at the given shop from the

expenses-file>[items-list];

[items-list]<Calculate the total cost>[total]

[expenses-file, shop-name]<Obtain all items purchased at the given shop from the

expenses-file>[items-list] ---> {[expenses-file]<Get the next item>[item]; [item]<Put the item on items-list>[items-list]

|item.shop = shop-name

}not end of expenses-file

[items-list]<Calculate the total cost>[total] ---> { [items-list]<Get next item from the list>[item]; [item]<total := total + item.price>[total]

}not end of items-list

Advantages of PRN（ PRN のいいところ）

The name of an operation can be as long as necessary. Thus, one can choose freely the name that describes the function of the operation best. （長い操作名を使える）The order of defining operations is consistent with the way of developing design ideas. （操作定義の順番が重要でない）PRN has a good readability, due to both the clear syntax and the way to define operations. （ PRN設計書は読みやすい）

PRN can be easily translated into a programming language, e.g., C, Java.（ PRN 設計からプログラムへの変換を行いやすい）PRN takes less space than the graphical notations, such as the Structure chart, Jackson Structure Diagram, Flowchart, and N-S Diagram. （ PRN 設計書は、図言語より小さい紙面を占める）

5.6 Java-based pseudocode（ Java 擬似コード）

Pseudocode is similar to a program code, but allows the use of natural language (e.g., English) for abstraction of functions. These functions are usually complex at the time and they need further decomposition, to be performed at later stage. （擬似コードは、プログラムコードに似ているが、ある部分を自然言語で表現する）

Java-based pseudocode is similar to program code written in Java; that is, the pseudocode structure is similar to that of a Java program, but natural language descriptions are allowed to abstract complex functions.（ Java 擬似コードとは、 Java 言語の構文に基くある部分の機能を自然言語で表現したプログラムのようなものである）

Pseudocode is suitable for detailed design. （擬似コードは詳細な設計に適切である）

The difference between Structured English and Pseudocode

（構造化英語と擬似コードの違い）

In Structured English we emphasize the use of English, but expect to improve its structure by using programming language constructs, such as sequence, choice, and iteration. While in pseudocode we emphasize the use of programming language, but to expect to improve its readability by using proper English for abstract description of functions.

Example （擬似コードの事例）

A pseudocode for computing the average of 10 integers:

int a[] = new int[10];

int total = 0, count = 0;

double average = 0;

Input 10 integers to array a;

Obtain the total of the integers in array a;

average = (double) total / a.length;

Decomposition （分解）Obtain the total of the integers in array a:

while (count < a.length)

{

total += a[count];

count++;

}

Advantages of pseudocode（擬似コードの長所 )

It is easy to learn, if one knows the specific programming language well. （勉強しやすい）It is natural and effective for detailed designs. （詳細な設計に対して、有効及び自然的な表現である）It is easy to be translated into program code. （プログラムコードへの変換をしやすい）

Disadvantage of pseudocode（擬似コードの短所）

Pseudocode is usually language-specific, therefore, it is not suitable for high level design. （擬似コードは、一般にプログラミング言語に依存するので、抽象設計には、適切でない。

Exercise 5

1. Use Structured English to describe the following Jackson Structure Diagram. （次の Jackson Structure Diagram を Structured English で表現しなさい）

RegisterItems

RegisterOne Item

RegisterItem Name

RegisterItem Price

RegisterItem Shop

RegisterItem Date

RegisterAs Food

RegisterAs Others

*

2. Give a flowchart describing the following Jackson Structure Diagram. （フローチャートで次のJackson 　 Structure 図を表現しなさい）

RegisterItems

RegisterOne Item

RegisterItem Name

RegisterItem Price

RegisterItem Shop

RegisterItem Date

RegisterAs Food

RegisterAs Others

*

3. Give a N-S diagram for the flowchart resulted from problem 2. （課題２で作成されたフローチャートを N-S 図で表現しなさい）

4. Give a Java-based pseudocode for the following PRN operation definitions: （次の PRN 設計書を Java 擬似コードで表現しなさい）

[expenses-file, shop-name]<Calculate the total cost of all items purchased at the given shop>[total]

---> [expenses-file, shop-name]<Obtain all items purchased at the given shop from the expenses-file>[items-list]; [items-list]<Calculate the total cost>[total]

[expenses-file, shop-name]<Obtain all items purchased at the given shop from the

expenses-file>[items-list] ---> {[expenses-file]<Get the next item>[item]; [item]<Put the item on items-list>[items-list]

|item.shop = shop-name

}not end of expenses-file

[items-list]<Calculate the total cost>[total] ---> { [items-list]<Get next item from the list>[item]; [item]<total := total + item.price>[total]

}end of items-list

5. Give a Jackson Structure Diagram describing the following PRN operation definitions: （次の PRN 操作の定義を Jackson Structure 図で表現しなさい）

[x1, x2]<A>[y1, y2, y3] ---> [x1]<B1>[z1]; [z1]<B2>[y1];

[x2]<B3>[y2] | x2 > 0 [x2]<B4>[y3] [x1]<B1>[z1] ---> <z1 := x1 + 5> [z1]<B2>[y1] ---> <y1 := 0>;

{<y1 := y1 + z1>; <z1 := z1 – 1>}z1 > 0

Hint: there is no need to consider the detailed conditions in the generated Jackson Structured Diagram.