© Chinese University, CSE Dept. Software Engineering / 5 - 1 Software Engineering Topic 5: Software Design Your Name: _____________________ Computer Science

© Chinese University, CSE Dept. Software Engineering / 5 - 1

Software Engineering

Topic 5: Software Design

Your Name: _____________________

Computer Science & Engineering Department

The Chinese University of Hong Kong


Prelude

Software design should be based on s/w engineering principles– Rigor and formality

» Appropriate notations for design– Separation of concerns, Modularity, Abstraction

» Handle design complexity, make s/w understandable and reliable

– Anticipation of change, Incrementality» Produce evolvable s/w design

– Generality» Product family


Prelude

Software design should be based on s/w engineering principles– Rigor and formality

» Appropriate notations for design– Separation of concerns, Modularity, Abstraction

» Handle design complexity, make s/w understandable and reliable

– Anticipation of change, Incrementality» Produce evolvable s/w design

– Generality» Product family


Prelude

High quality design – modular structure– decomposition criteria

Information hiding: a module is characterized by the information it hides from other modules ___________– Information hiding + abstract data type

O-O design – _____________design

Stepwise refinement: __________ design


Top-down vs. Bottom-up Designs

Top-down design Bottom-up design


Software Design Activity

Software design– system decomposition into ____________

Description of a)functions of each module => ____-module

b)interfaces between modules => ____-module

the software structure (architecture)


Implement

Design for change – A design that is flexible enough to accommodate

changes easily

e.g. “___________” for constant names in C

Software Design Activity

M

M

M

M

Decompose

1

2

3


What Changes?

Change of algorithms– to improve efficiency, generality– e.g. sorting algorithm (____________ ____________)

Change of data structure (17% maintenance cost) – e.g. arrays vs linked lists– Data structures representing a Tree

Change of underlying abstract machine– Hides details of the underlying h/w– e.g. complier, database, OS

Change of peripheral devices– e.g. printers, terminals, Microsoft experience

Change of social environment– e.g. tax, social habits, currency changes


What Changes?

Change of algorithms– to improve efficiency, generality– e.g. sorting algorithm (____________ ____________)

Change of data structure (17% maintenance cost) – e.g. arrays vs linked lists– Data structures representing a Tree

Change of underlying abstract machine– Hides details of the underlying h/w– e.g. complier, database, OS

Change of peripheral devices– e.g. printers, terminals, Microsoft experience

Change of social environment– e.g. tax, social habits, currency changes


Data Structure Representing a Tree (1)


Data Structure Representing a Tree (2)


Product Families

A set of different versions of a program, due to– different h/w or s/w

– different environment with different requirements on performance or resource consumption

– system evolution due to new requirements or quality improvement

– Usually with the same basic set of functional requirements


Product Families

The solution:– minimize the cost of changing design decisions

Necessary tools to manage product families:

» ____________________________ tools


Sequential Completion:A Graphical View

Requirements

1

2

3

Version 1

Version 1

Version 2 5

Requirements

1

2

3

4 6

7 Version 3

4

Requirements

1

2

3

Version 2 5

Version 1

4

____________

__________


Modularization Techniques

Architecture design (overall structure) Detailed design (design of each module by

“information hiding”) WBS (Work Breakdown Structure):

– A description of the product hierarchy


Software Work Breakdown Structure: Product Hierarchy

Part of the final product

Describe how the work is to

be done

Software System (SS)

Subsystem (SS N)Subsystem (SS A) System (SS)activities

Subsystem(SS AA)

Subsystem(SS AM)

Subsystem (SS A)activities

Subsystem(SS AAA )

Subsystem(SS AAK )

Subsystem (SS AA)activities

SAAA SAAK SAA1-SAA6

SAA SAM SA1-SA6

SA SN S1-S6

S


(1) Overall Structure

Module - a well-defined component of a s/w system– self-contained

– with clear boundary

– collection of» Routines (.c)

» Data

» Type_definitions (.h)



Notationlet S be a s/w system, composed of modules M1, M2 ,…, Mn

i.e., S = { M1,M2,…,Mn }

A relation r on S is a subset of S×S

( cardinality = ______________ )

i.e., r: module × module Boolean

We say Mi is related to Mj (both in S) iff Mi r Mj is true.

( e.g. r: “call” )



The relations for modules i. ___________: ¬(Mi r Mi)

ii. contain _______________: Mi r+ Mj

iff Mi r Mj or Mk Mi r Mk and Mk r+ Mj

iii. ________(________):if Mi r+ Mj ¬(Mj r

+ Mi)

A hierarchy relation means there are no __________ in the graph of the relation

» directed acyclic graph (DAG) » vs. general graph (Figuer 5.1)



General Graph Directed Acyclic Graph (DAG)

Level___

___

___

___

___

M1

M2M3

M4

M1,1 M1,2 M1,3

M1,2,1 M1,2,2

M1,2,1,1

M

M M

M M

M

1

2 3

4 5

6

a) b)

Figure 5.1 Graph representation of a relation among modules, (a) General graph, (b) Direct acyclic graph (DAG)


Levels in a Hierarchy Relation

– LEVEL0: {Mi | Mj S Mi r Mj}

“_________________________________________________________________________________________

_________________________________________”

– LEVELk+1: {Mi | Mj LEVELk Mi r Mj and Mm

S, Mi r Mm Mm LEVELm, m [0,…,k] }

“_________________________________________________________________________________________

_____________________________”

– module Mi is “higher level” than module Mj iff Mi

LEVELi and Mj LEVELj and i > j


The USES Relation

–For Mi, Mj S, Mi USES Mj iff correct

execution of Mj is necessary for Mi to be

correct »Mi is a client of Mj

»An obvious USES example is when Mi and its

correctness depend on a call to a procedure in module Mj

–Q: Is _________________ equivalent to __________________ relation?


USES Is Not Equivalent to Calls

a) procedure calls are not the only way for modules to interact (Not all USES are calls)

−E.g.1 in assembly, a module may modify local data or instructions of another module

−E.g.2 _______________________

C: _________________

Fortran: _____________

General: __________Variables

write read


USES Is Not Equivalent to Calls

– E.g.3 exchange of control information (_____)

– E.g.4 in sequential environment, modules may communicate via parameter passing through subprograms

– E.g.5 in concurrent environment, modules may communicate via messages passing through tasks

b)Not all calls are USES» E.g. calling for reporting exceptions


USES Relation

USES relation is static, i.e., independent of the execution of the s/w:in Module M:

“if cond then proc1 else proc2”

in M1 in M2 “ “ USES


USES Relation

For a good design, USES relation should be hierarchy

i. easy to understand− “separation of concerns” => used components first, then their

clients

ii. easy to implement − “incrementality” otherwise, “we may end up with a system

in which nothing works until everything works.”

iii. easy to define structure− “levels of abstraction” high-level modules (clients) first,

then low-level (used) modules

(iii) _________________ design (i)(ii) ________________ implementation


How to Build Hierarchy Relations?

Key: decoupling modules to avoid recursion among modules.

1. recursion within a module does not affect the relation among modules

2. consider an alternative algorithm which does not require recursion

3. if two modules have to USES each other recursively, group them together into one large module


How to Build Hierarchy Relations?

4. consider splitting one module into two:

M M3M

M3


IS_COMPONENT_OF Relation

Let S be a set of modules M1,M2,…,Mn

for any Mi,Mj S, Mi IS_COMPONENT_OF Mj means

“Mj is realized by several modules, one of which being Mi”

Mj COMPRISES Mi

Let Ms,i be a subset of S where

Ms,i = { Mk | Mk S and Mk IS_COMPONENT_OF Mi}

then we say

Mi IS_COMPOSED_OF Ms,i or Ms,i IMPLEMENTS Mi


• M7 is component of _____

• _______ comprises M7

• _______________ implements M2

• M2 is composed of ___________________

M1

M M

M MM M M

2 4

5 67 8 9

M 3

M MM M M5 67 8 9

M2 M 3 M4

M1

(IS_COMPONENT_OF) (COMPRISES)

Figure 5.2 An example of the IS_COMPONENT_OF relation


Notations for a Design

In a design, once Mi is decomposed into the

set Ms,i, it is replaced by them in the

implementation; Mi becomes merely an

abstraction for that implementation Physically, the final implementation only

contains the “leaf” modules in a COMPRISES relation graph


Product Families Revisited

Is-composed-of

M3,3M3,2M3,1

M3

Uses

M7

M3

M5M6

M2 M4

M1

Uses

Version 1

Design Decision 1

Design Decision 2

Version 2Uses

M1

_______M4

_______ _______

M2

M1

_______M4

_______ _______

M2


Design Level Visibility

Data flow level

Structure chart level

“______________”


A Good Design Hierarchy

1. Partition the design: ________ vs ________

2. there is more than one level

3. there aren’t too many levels

4. for each Mi S, the set of modules

{Mj | Mi r Mj } to which it USES is small

“low ________” – number of outgoing edges of a module

( example )


A Good Design Hierarchy

5. for each Mi S, the set of modules (clients)

{Mj | Mj r Mi} which USES Mi is large

“high _______” – number of incoming edges of a module

6. ______ cohesion– internal connections in a module

______ coupling– external connections among modules




Interface, Implementation, and Information Hiding

In the USES relation, the set of services that each module provides to its clients is called ________________– The services are exported by the used modules and

imported by the clients

The interface is an _____________ of the module as viewed by its clients

A designer of module M only needs to know the interfaces of other modules used by M, and may ignore their ________________.


Interface, Implementation, and Information Hiding

Interface – _________________________– _________________________– _________________________

In summary, the clients of a module know about its services only through its interface, the implementation is hidden from them Information hiding, an important concept for software engineering principles


How to Design Interfaces Facilitating Information Hiding?

The interfaces should be as simple as possible, but not simpler

identify changeable design decisions and unchangeable module informationi. unchangeable information

________________ (stable)

ii. changeable design decisions “secret” (hidden in the ________________)

We say such information is ________________ within the module implementation.


Typical Secrets

1. The algorithm for carrying out some operation, e.g. algorithms for sorting routine

2. The representation of some data structure, e.g. abstract data type

– Clients know how to operate it, but do not know how it is implemented

3. The details of an interface to the abstract machine underlying the s/w

4. The policy for allocating some resource or ordering certain operations (e.g., PRINT a sorted list)

5. Abstract data type


Abstract Data Type

Abstract data type is an information hiding module where the representations of data structures are encapsulated.

– e.g. A “stack” could be defined in only four operations in its interface: _____,____,____, init


A Note About Architectural Design

A precise definition of the interface is necessary for module (re)usability– High _________; High __________

The interface must contain all the information that is needed to characterize the module’s behavior, and nothing more– Low __________


Procedures for Architectural Design

1. Apply USES and IS_COMPONENT_OF Notations

2. Build hierarchy relations (avoid recursion)3. Identify modules with high cohesion and low

coupling4. Design interface5. Hide information6. Reduce design complexity => exercise


(2) Detailed Design

s/w design notations– formal in syntax

– informal in semantics

1. TDN (Textual Design Notation)

2. GDN (Graphical Design Notation)


TDN: Textual Design Notation

key sections (_________)– module

– uses

– exports » var, type, procedure (________)

– implementation » list internal components

– end

____________

__________ relation

__________

__________ relation

Examples (Figure 5.3, Figure 5.4, Figure 5.5)


Figure 5.3 A Sample Module Description

module Xuses Y, Zexport

var A: integer;type B: array (1..10) of real;procedure C(D: in out B; E in integer; F: in real)

______________________________

Implementation

______________________________is composed of R, T

end X


module Xuses Y, Zexport

var A: integer;type B: array (1..10) of real;procedure C(D: in out B; E in integer; F: in real)

Here is an optional natural language description of what A, B and C actually are, along with possible constraints or properties that clients need to know; for example we might specify that objects of type B sent to procedure C should be initialized by the client, and should never contain all zeros.

Implementation If needed, here are general comments about the rationale of the

modularization, hints on the implementation, etc.

is composed of R, Tend X

Figure 5.3 A Sample Module Description


Figure 5.4 Sample Components of Module X

module Ruses Yexport

var K: record … end;type B: array (1..10) of real;procedure C(D: in out B; E in integer; F: in real)

Implementation

…

end R

module T

uses Y, Z, R

exports var A: integer;

implementation

…

end T


Figure 5.5 An Example of a Module with Selective Import

module Wuses X imports(B,C),

XXexports …implementation

.

.

.end W

X exports _____________;only ________ are imported here; referred as ___________.

XX resources ____________.


TDN

A TDN design takes some time to comprehend

TDN can provide various levels of details – e.g., ______________ in great detail

The designer needs to check for consistency and completeness

The tedious checking procedure should be automated if possible

A more complicated example follows.


Example: A “MINI” Compiler

module COMPILERexports procedure MINI ( PROG: in file of char;

CODE: out file of char);MINI is called to compile the program stored in PROG and produce the object code in file CODE

implementationA conventional compiler implementation ANALYZER performs both lexical and syntactic analysis and

produces an abstract tree as well as entries in the symbol table:CODE_GENERATOR generates code starting from the abstract

tree and information stored in the symbol table. Module MAIN acts as a job coordinator.is composed of ANALYZER, SYMBOL_TABLE,

ABSTRACT_TREE_HANDLER,CODE_GENERATOR, MAIN

end COMPILER



module MAINuses ANALYZER, CODE_GENERATORexports procedure MINI(PROG: in file of char;

CODE: out file of char); .

.end MAIN

module ANALYZERuses SYMBOL_TABLE, ABSTRACT_TREE_HANDLERexports procedure ANALYZE(source :in file of char);

SOURCE is analyzed; an abstract tree is produced by using the services provided by the handler, and recognizedentities, with their attributes are stored in the symbol table.

end ANALYZER



module CODE_GENERATOR

uses SYMBOL_TABLE, ABSTRACT_TREE_HANDLER

exports procedure CODE(OBJECT: out file of char);

The abstract tree is traversed using the operations exported by the ABSTRACT_TREE_HANDLER and accessing the information stored in the symbol table in order to generate code in the output file.

.

.

.

end CODE_GENERATOR


GDN (Graphical Design Notation)

a box represents a ___________ incoming arrows represent a module’s

__________, i.e., exported ___________ not to be confused with DFD can also show “IS_COMPOSED_OF” and

“IS_COMPONENT_OF” relations


Figure 5.6 Graphical description of module X of Figure 5.3

Figure 5.6 GDN of Module X

X

Y

Z A B

R T Module Module

Module

Module

Module

C


Figure 5.7 X’s Decomposition

Figure 5.7 Module X is composed of modules R and T

X

Y

Z B C

R T Module Module

Module

Module

Module

A

K


Module M

Module L Module N

Module M

Module R

Module M

Module S

Module H Module G

Figure 5.8 Module M is a member of both L and N

A

B

K

Module M

IS_COMPONENT_OF what?

_________________

IS_COMPOSED_OF what?

_________________

Exports what?

_________________

USES what?

_______ (which exports _______ )Module F


GDN (Graphical Design Notation)

It provides “s/w design visualization” It is useful in comprehending complicated s/w

(e.g., concurrent s/w) It may take too much space It is useful for high-level view of the s/w design Detailed levels need to be automated (CASE)

– E.g. Statemate, Teamwork, Rational, UML


Categories of Modules

1) Procedural abstractions– purpose: to encapsulate an ____________

– e.g.: sorting module, fast Fourier transform module

2) Libraries– purpose: to group together related

___________________________

– e.g.: » mathematical routines

» graphical routines



3) Common pool of data– purpose: to share _______ among several

modules

– e.g.: system configuration constants group

– note:



4) Abstract objects– purpose: to hide the details of data __________

(change of data structures is _________ of cost for total software maintenance)

– e.g.: a symbol-table

– note: exhibit a state



5) Abstract data type– purpose: to hide the ___________ of a data type

and the algorithms used in ________ the objects of that type

– e.g.:» Stack» Ada - private type» Module-2 - opaque type

– note:i) no stateii) can generate many instances (___________)


Stack as an Abstract Data Type

Module STACK_HANDLERexports

type STACK : ?; This is an abstract data type module; the data structureIs a secret hidden in the implementation part.procedure PUSH(S: in out STACK; VAL: in element);procedure POP(S: in out STACK; VAL: out element);function EMPTY(S: in STACK): BOOLEAN;function TOP(S: in STACK): element;procedure INIT(S: out STACK);

end STACK_HANDLER

A new symbol to export a _______________, leaving implementation detail hidden.


Stack Implemented as an Array

stack: record sp: integer; arr: array[1..Max] of element end; procedure Push(e:element) is begin stack.sp := stack.sp + 1; stack.arr[stack.sp] := e; end; procedure Pop is begin

stack.sp := stack.sp -1; end; function Top return element is begin return stack.arr[stack.sp]; end; procedure Init is begin stack.sp := 0; end;


Stack Implemented as a List type stackptr;type stackelement is record elem: element; next: stackptr; end record;type stackptr is access stackelement;stack: stackptr;procedure Push(e:element) is item: stackptr; begin item := new stackelement;item := e;item.next := stack;stack := item; end;procedure Pop is begin

stack := stack.next; end;function Top return element is begin return stack.item; end;procedure Init is begin stack := null; end;


Yet Another Example of Abstract Data Type

module FIFO_CARSuses CARSexports

type QUEUE :?;procedure ENQUEUE(Q: in out QUEUE; C: in CARS);procedure DEQUEUE(Q: in out QUEUE; C: out CARS);function IS_EMPTY(Q: in QUEUE) :BOOLEAN;function LENGTH(Q: in QUEUE): NATURAL;procedure MERGE(Q1, Q2: in QUEUE; Q: out QUEUE);

end FIFO_CARS Declaration of the type QUEUE: gasoline_1, gasoline_2, gasoline_3 : QUEUE;car_wash :QUEUE; Operations on the type QUEUE: ENQUEUE(car_wash, that_car);MERGE(gasoline_1, gasoline_2, gasoline_3);


More Techniques for Design for Change

Configuration constants – Constants which might be changed due to

different configuration

– E.g., a :array(1..N) of integer;

N = 100;

– these configuration constants could be grouped into a module that provides

____________________


More Techniques for Design for Change Conditional compilation

– All versions of a program family are represented by one single source copy, and the differences between various versions are determined by condition compilation

– … {portion common to all versions}#ifdef h/w-1 {compiled portion if h/w–1 is true}#endif#ifdef h/w-2 {compiled portion if h/w–2 is true}#endif

Software Generator– yacc - compiler generator– user interface generator– executable specification language


Stepwise Refinement

a popular method for describing the logical structure of a given algorithm, implemented by a single module

stepwise refinement is an effective way of describing a solution after it has been partially obtained (software engineering principle: _______________)


Example: Derivation of Selection Sort

Step 1let n be the length of the array a to be sorted;i := 1 ;while i < n loop

find the smallest of ai .. .an, and exchange it with the element at position i;i := i + 1;

end loop;


Step 2let n be the length of the array a to be sorted;i := 1 ;while i < n loop

j := n;while j > i loop

if a(i) > a(j) theninterchange the elements at

positions j and i ;end if;j := j - 1;

end loop;i := i + 1;

end loop;


Step 3let n be the length of the array a to be

sorted;i := 1 ;while i < n loop

j := n;while j > i loop

if a(i) > a(j) thenx := a(i); a(i) := a(j); a(j) := x;

end if;j := j - 1;

end loop;i := i + 1;

end loop;


Stepwise Refinement

P 2

P

P 1 P 3

P 2,1

P 2,1,1 P 2,1,2

C

C 1 not C 1

Figure 4.13 Graphical representation of stepwise refinement.

[While C loop P2,1]]

[ If C1 then P2,1,1

Else P2,1,2]

Step 0

Step 1

Step 2

Step N


Stepwise Refinement

It is a method that works in the small, but fails in the large. Here are the reasons:

1. sub-problems tend to be analyzed in isolation, reducing ______________

2. No attention is paid to _______________

3. No attention is paid to _______________

4. The ________ function may not exist

5. A premature commitment to the ____________ structures


A Short Summary About Design

stepwise refinement– top-down design

information hiding– bottom-up design

combining both– yo-yo design

1. design should use both schemes

2. description of the resulting design should be ______________


Handling Anomalies

To achieve reliable solutions– Systematic design approach

– Rigorous and disciplined implementation

One solution: employ __________ design – Purpose: build robust systems

– The program should continue to behave reasonably even in the case of unexpected and unforeseen circumstances


Handling Anomalies

Anomalous – if a module fails to provide a service as expected and specified in its interface– _________ – to be associated with a service,

denoting the anomalies that may occur while that service is being performed


Handling Anomalies

Defensive design requires that upon entering an anomalous state, the module should signal the anomaly by raising an exception to the client

The server module terminates the service after _________ an exception; the client responds by suitably ________ the exception


Why an Exception is Raised by a Module, say M?

1. M’s client does not satisfy the required protocol for invoking one of M’s service

2. When providing a service to its client, M does not invoke a service exported by another module properly

3. M fails to provide its service because of an unforeseen condition


M’s server

M

M’s client

__

__

__

M’s server

C;

M’s clientA

B

C

B;

______ an exception

______ an exception

_____ the exception

M:


Module M

module Mexports . . .

procedure P (X: INTEGER; . . .) raises X_NON_NEGATIVE_EXPECTED,

INTEGER_OVERFLOW;X is to be positive; if not, exceptionX_NON_NEGATIVE_EXPECTED is raised;INTEGER_OVERFLOW is raised if internalcomputation of P generates an overflow

.

.

.

end M


Module L

module L

uses M imports P (X: INTEGER; . .) .) exports . . .;

procedure R ( . . .) raises INTEGER_OVERFLOW;

.

.

. implementation

If INTEGER_OVERFLOW is raised when P is invoked, the

exception is propagated . . .

end L


Concurrent Software

The case of a module defining shared data E.g., abstract object BUFFER

– module QUEUE_OF_CHAR is GENERIC_FIFO_QUEUE (CHAR)

– BUFFER : QUEUE_OF_CHAR.QUEUE

with operations– PUT: inserts a character in BUFFER– GET: extracts a character from BUFFER – NOT_FULL: returns true if BUFFER not full – NOT_EMPTY: returns true if BUFFER not empty


How to Control Correct Access to Shared Data?

Not sufficient that clients check operation invocations, such as

if QUEUE_OF_CHAR.NOT_FULL (BUFFER) then QUEUE_OF_CHAR.PUT (X, BUFFER);

end if;

Consumer_1 and Consumer_2 might do this concurrently

» if only one slot is left, both may find the buffer not full, the first who writes fills it, and the other writes in a full buffer


Enforcing Synchronization

Ensure that operations on buffer are executed in mutual exclusion

Ensure that operations such asif QUEUE_OF_CHAR.NOT_FULL (BUFFER) then

QUEUE_OF_CHAR.PUT (X, BUFFER);

end if;

are executed as logically non-interruptible units


Monitors

Abstract objects used in a ____________ environment

Available in the Java programming language


Monitors: an Example

concurrent module CHAR_BUFFER This is a monitor, i.e., an abstract object module in a concurrent environment

uses . . . exports

procedure PUT (C : in CHAR) requires NOT_FULL; procedure GET (C: out CHAR) requires NOT_EMPTY; NOT_EMPTY and NOT_FULL are hidden Boolean functions yielding TRUE if the buffer is not empty and not full, respectively. They are not exported as operations, because their purpose is only to delay the calls to PUT and GET if they are issued when the buffer is in a state where it cannot accept them . . .

end CHAR_BUFFER


Comments on Monitors

Monitor operations are assumed to be executed in _________________

A requires clause may be associated with an operation– it is automatically checked when operation is

called– if the result is false, the current process is

suspended until it becomes true (at that stage it becomes eligible for resumption)


Monitor Types: an Example

generic concurrent module GENERIC_FIFO_QUEUE (EL) This is a generic monitor type, i.e., an abstract data type accessed in a concurrent environment

uses . . . exports

type QUEUE: ?; procedure PUT (Q1: in out QUEUE; E1: in EL)

requires NOT_FULL (Q1: QUEUE); procedure GET (Q2: in out QUEUE; E2: out EL)

requires NOT_EMPTY(Q2: QUEUE); . . .

end GENERIC_FIFO_QUEUE (EL)


Guardians and Rendez-vous

The Ada style of designing concurrent systems

In Ada a shared object is ___________ (whereas a monitor is ____________)– it is managed by a guardian process which can

accept rendez-vous requests from tasks willing to access the object


A Guardian Task

loopselect

when NOT_FULL accept PUT (C: in CHAR);This is the body of PUT; the client calls it as if itwere a normal procedureend ;

orwhen NOT_EMPTY

accept GET (C: out CHAR);This is the body of GET; the client calls it as if itwere a normal procedure

end ;end select ;

end loop ;

note _______________ acceptance ofrendez-vous requests


Real-Time Software

A case where processes interact with the _______________

E.g., a put operation on a shared buffer is invoked by a plant sensor sending data to a controller– plant cannot be suspended if buffer full!

» design must ensure that producer never finds the buffer full

» this constrains the speed of the consumer process in the controller


TDN Description

concurrent module REACTIVE_CHAR_BUFFER This is a monitorlike object working in a real-time environment. uses . . . exports

reactive procedure PUT (C: in CHAR); PUT is used by external processes, and two consecutive PUT requests must arrive more than 5 msec apart; otherwise, some characters may be lost procedure GET (C: out CHAR); . . .

end REACTIVE_CHAR_BUFFER


GDN Description

Module

REACTIVE_CHAR_BUFFER

PUT GET

zig-zag arrow indicates ______________ invocation


Distributed Software

Issues to consider– module-machine binding

– intermodule communication» e.g., remote procedure call or message passing

– access to shared objects» may require replication for efficiency reasons


Client-Server Architecture

The most popular distributed architecture Server modules provide services to client

modules Clients and servers may reside on different

machines


Issues

Binding modules to machines– static vs. dynamic (migration)

Inter-module communication– e.g., Remote Procedure Call (RPC)

– To define interface of remote procedures

Replication and distribution


Middleware

Layer residing between the network operating system and the application

Helps building network applications Provides useful services

– _____________ services, to find processes or resources on the network

– ______________ services, such as message passing or RPC (or RMI)


A Further Relation: Inheritance (Generalization – Specialization)

The keyword in (pure) object-oriented design: “inheritance” - to form a class of objects. – e.g., “class” in C++ (public, private, protected)

– e.g., “extends” in Java creates “subclasses”

ADTs may be organized in a hierarchy Class B may specialize class A

– B inherits from A

conversely, A generalizes B A is a superclass of B B is a subclass of A


Key Concept in O-O Design: Inheritance A new relation: INHERITS_FROM If M1 INHERITS_FROM M2, then M1 has visibility into

the internal structure (the _______) of M2 a hierarchy relation

1. _____________________

2. _____________________

3. _____________________

M1 INHERITS_FROM M2

– M2: parent module

– M1: heir module


An Inheritance Example in TDN

class EMPLOYEE exports

function FIRST_NAME(): string_of_char; function LAST_NAME(): string_of_char; function AGE(): natural; function WHERE(): SITE; function SALARY: MONEY; procedure HIRE (FIRST_N: string_of_char;

LAST_N: string_of_char; INIT_SALARY: MONEY);

Initializes a new EMPLOYEE, assigning a new identifier. procedure FIRE(); procedure ASSIGN (S: SITE); An employee cannot be assigned to a SITE if already assigned to it (i.e., WHERE must be different from S). It is the client’s responsibility to ensure this. The effect is to delete the employee from those in WHERE, add the employee to those in S, generate a new id card with security code to access the site overnight, and update WHERE.

end EMPLOYEE

Figure 5.9 An Example of Inheritance: TDN


class ADMINISTRATIVE_STAFF inherits EMPLOYEE exports

procedure DO_THIS (F: FOLDER); This is an additional operation that is specific to administrators; other operations may also be added.

end ADMINISTRATIVE_STAFF class TECHNICAL_STAFF inherits EMPLOYEE exports

function GET_SKILL(): SKILL; procedure DEF_SKILL (SK: SKILL); These are additional operations that are specific to technicians; other operations may also be added.

end TECHNICAL_STAFF

Figure 5.9 An Example of Inheritance: TDN


An Example of Inheritance: GDN

Module EMPLOYEE

Module

ADMINSTRATIVE

STAFF

Module

TECHNICAL

STAFF

GET_SKILLDEF_SKILL

DO_THIS

NAMEAGE

WHEREModule SITE

... to modules MONEY

exportsuses

_________

________

_____________________

Module

FOLDER

Module

SKILL

________


Properties of Inheritance

Inheritance allows a hierarchical classification scheme for abstract data types through generalization-specialization relations– distinguish commonalities and differences among

a (potential) set of abstract objects

– commonalities are factored out in a ________ class

– variations are singled out in the ___________ classes



Inheritance improves reusability - ________ class

Inheritance is a way of building software ______________

Disadvantage of inheritance



A subclass defines a subtype– subtype is substitutable for parent type

Polymorphism– a variable referring to type A can refer to an object

of type B if B is a subclass of A

Dynamic binding – the method invoked through a reference depends on

the type of the object associated with the reference at runtime


Several (Controversial) Extensions

Redefinition: an heir product provides a different implementation for one of its parent’s services – e.g., change of the sorting algorithm regarding its implementation

(no change to interface) – _______ and _________ allow it; ________ does not

Redefinition applied to the data structure hidden in the parent module

Multiple inheritance: define a new module by combining the feature provided by two or more parent modules – e.g., FIFO_QUEUE, EMPLOYEE– ________ allows it, but _________ and _________ do not


Using UML in Software Design

UML (Unified Modeling Language) notation is popular in software engineering.

UML is a collection of languages that provide specific notations to specify, analyze, visualize, construct, and ________ software.

UML is a widely adopted standard notation for representing OO designs

We introduce the UML class diagram– classes are described by boxes


UML Representation of Inheritance

EMPLOYEE

TECHNICAL_STAFF ADMINISTRATIVE_STAFF

Note: similar to __________


UML Associations Associations are relations that the

implementation is required to support Can have multiplicity constraints

TECHNICAL _STAFF

MANAGER

PROJECT * 1 project_member

1

1..* manages


UML Aggregation

Defines a PART_OF relationDiffers from IS_COMPOSED_OF

Here TRANGLE has its own methods

It implicitly uses POINT to define

its data attributes

TRIANGLE

POINT

1

3


More on UML

UML evolves from TDN/GDN USES relationship is refined with semantically richer relationship: inheritance,

association, and aggregation– If class B inherits from class A, B USES A => ___________ USES _________– Association between classes implicitly define USES relation => ___________ USES

____________– If B aggregates A, B USES A => __________ USES __________

Representation of IS_COMPONENT_OF via the package notation

package_name

Class 1

Class 2

Class 3


Software Architecture

Describes overall system organization and structure in terms of its major constituents and their interactions

Standard architectures can be identified– pipeline

– blackboard

– event based (publish-subscribe)


Standard Architectures

PipelineExample: _________________

event basedExample: _______________

_______________________

BlackboardExample: ____________ ,

_________________


Domain Specific Architectures

"model–view–controller" architecture for software that has a significant amount of user interaction

Model (store data e.g. text)

Controller (interact with user; perform commands)

View (display model for user)


Software Components

Goal– build systems out of pre-existing libraries of

components

– as most mature engineering areas do

Examples– STL (Standard Template Library) for C++

– JavaBeans and Swing for Java

– .NET (including COM objects and DLL libraries)


Component Integration

The CORBA (Common Object Request Broker Architecture) Middleware

Clients and servers connected via an Object Request Broker (ORB)

Interfaces provided by servers defined by an Interface Definition Language (IDL)

Existing paradigm: Web Services Current trend: Cloud Computing + Mobile Apps


Architectures for Distributed Systems

From two tiered– Client-server

to three tiered

Requests for service (database)

Web browser

(client)

Web server (server) Requests

for service (pages)

User interface

(client)

Decode

service

request (2nd tier)

Application

server (databse)


Program Implementation Techniques

1. Programming Standards and Procedures Need for standards and procedures

A uniformed good programming style helps understandability, consistency, correctness of a team project.

a) Standards for You Standards and procedures help you ____________ your thoughts and avoid mistakes; they also help in ____________ design to code

b) Standards for OthersIt is essential you organize, format, and document your code to make it easy for others to understand what it does and how it works.



Matching _______ with _______________– Direct correspondence

between the program design modules and the program code modules

– Keep up with the good design for traceability and maintainability

– Use header file to trace module design

/***************************************** MODULE TO FIND INTERSECTION OF TWO LINES * MODULE NAME: FINDPT* PROGRAMMER: HU-AIM EYE* VERSION: 1.0 (3 MARCH 15)** PROCEDURE INVOCATION:* CALL FINDPT (A1, B1, C1, A2, B2, C2, XS, YS, FLAG)** INPUT PARAMETERS:* INPUT LINES ARE OF THE FORM* A1*X + B1*Y + C1 = 0 AND* A2*X + B2*Y + C2 = 0* SO INPUT IS COEFFICIENTS A1, B1, C1 AND* A2, B2, C2* * OUTPUT PARAMETERS:* IF LINES ARE PARALLEL, FLAG SET TO 1.* ELSE FLAG = 0 AND POINT OF INTERACTION* IS (XS, YS).*****************************************/



2. Programming Guidelines– Control structures

– Algorithms

– Data structures

– General guidelines


Control Structures

Using Fundamental Constructs

Main ingredients for structured programs:

1. ______________e.g.,___________________

2. ______________e.g.,___________________

3. ______________e.g.,___________________


________ ________

Control Structures


__________

OR

Control Structures

____________ ____________


Control Structures

Top-down FlowPrograms should be readable from the top down

Use of Submodules– Follow the design to build submodules (functions,

procedures, macros) for elemental functions

– Build general submodules for ____________

– Explain _________ of submodules, but not their details


Program Without Top-Down Flow

BENEFIT = MINIMUMIF (AGE < 75) GO TO A;BENEFIT = MAXIMUM;GO TO C;IF (AGE < 65) GO TO B;IF (AGE < 55) GO TO C;A:IF (AGE < 65) GO TO B;

BENEFIT = BENEFIT * 1.5 + BONUS;GO TO C;

B:IF (AGE < 55) GO TO C;BENEFIT = BENEFIT * 1.5;

C:Next statement


Program With Top-Down Flow

IF (AGE < 55) THEN BENEFIT = MINIMUM;ELSE IF (AGE < 65) THEN BENEFIT = MINIMUM + BONUS;ELSE IF (AGE < 75) THEN BENEFIT = MINIMUM * 1.5 +

BONUS;ELSE BENEFIT = MAXIMUM;


Algorithms

Program design often specifies a class of algorithms to be used

Efficiency of code should consider 1. ____________ of code

2. time to ______ the code

3. time to ______ the code

4. time for users to ___________ the code

5. time to ______ the code, if necessary


Data Structures

Keeping the Program Simple. Restructuring data can simplify a program.– Keep It Simple and Straightforward: _________

Using the Structure of Data to Determine the Structure of the Program

Localizing Input and Output in Separate Modules


General Guidelines

Using Pseudocode Revising and Rewriting Instead of Patching


Example of Program Simplification Using Data

Computing a tax due by: 1. For the first $10,000 of income, the tax is 10%. 2. For the next $10,000 above $10,000, the tax is

12%. 3. For the next $10,000 above $20,000, the tax is

15%. 4. For the next $10,000 above $30,000, the tax is

18%. 5. For any income above $40,000, the tax is 20%.


Program 1

TAX = 0.IF TAXABLE_INCOME = 0, GO TO EXITIF TAXABLE_INCOME > 10,000, TAX = TAX + 1000.

ELSE TAX = TAX + 0.10 * TAXABLE_INCOMEGO TO EXIT

IF TAXABLE_INCOME > 20,000, TAX = TAX + 1200.ELSE TAX = TAX + 0.12*(TAXABLE_INCOME – 10000.)GO TO EXIT

IF TAXABLE_INCOME > 30,000, TAX = TAX + 1500.ELSE TAX = TAX + 0.15*(TAXABLE_INCOME – 20000.)GO TO EXIT

IF TAXABLE_INCOME < 40,000, TAX = TAX + 0.18*(TAXABLE_INCOME – 30000.)GO TO EXIT

ELSE TAX=TAX+1800.+0.20*(TAXABLE_INCOME–40000.)EXIT: END


Program 2

Build a Sample Tax Table First:Bracket Base Percent0 0 1010,000 1000 1220,000 2200 1530,000 3700 1840,000 5500 20 The Program:LEVEL = 1

FOR I = 1 TO 4 DOIF ______________________________

THEN ___________________________

TAX = ______________________________________________________



3. Documentation Internal Documentation (documentation

associated with the program code)– Header Comment Block– Other Program Comments

– Meaningful Variable Names and Statement Labels


Header Comment Block

Specify 6 W’s 1. ______ your program is

2. ______ wrote the program

3. ______ the program fits in the general system design

4. ______ the program was written and revised

5. ______ the program exists

6. ______ your program uses its data structures, algorithms, and control


Sample

PROGRAM SCAN – Program to scan a line of text for a given character

PROGRAMMER: Wan, Lai-man 2609 8481CALLING SEQUENCE: CALL SCAN(LENGTH,CHAR)Where ‘LENGTH’ is the length of the line to be scanned, ‘CHAR’ is

the character to be sought, line of text passed as array ‘NTEXT’VERSION 1: written 2-2-2010REVISION 1.1: 3-3-2010 to improve searching algorithm.PURPOSE: General-purpose scanning module to be used for each

new line of text, no matter the length. DATA STRUCTURES: Variable LENGTH – INTEGER

Variable CHAR – CHARACTERARRAY NTEXT – CHARACTER array of length ‘LENGTH’

ALGORITHM: Reads array NTEXT one character at a time; if CHAR is found, position in NTEXT returned in variable ‘LENGTH’;

else variable ‘LENGTH’ set to 0

__________________

______

______

______



– Formatting to Enhance Understanding » _________________________________

» _________________________________

– Documenting Data

» _________________________________



External Documentation – Describing _________________ (what)

– Describing _________________ (how)

– Describing _________________ (how)


Topic 5 Conclusion

TDN, GDN Modularization techniques Information hiding Hierarchical relations Abstract objects and abstract data types Handling Anomalies Concurrent, real-time, distributed systems Architecture and components Program Implementation Techniques

Documents

© Chinese University, CSE Dept. Software Engineering / 5 - 1 Software Engineering Topic 5: Software Design Your Name: _____________________ Computer Science