a systematic approach to incorporate non-functional requirements into functional requirement...

8/4/2019 A Systematic Approach to Incorporate Non-functional Requirements Into Functional Requirement Modeling

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A systematic approach to incorporate

non-functional requirements into

functional requirement modeling


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Overview

Introduction

Motivation

Background

FR, NFR Integration Classpects

Use Cases and Their Sequence Digrams

Q-SIG

Conclusion


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Background

NFR-Framework Chung et.al, 1989-99

Treat NFRs as softgoals that need to besatisficied

Softgoal can not be absolutely fulfilled

Satsficing satisfying a requirement in avariety of degree without necessarily optimizing. e.g.. Somewhat, negatively, positively, very

positively

Consists of SIG (Softgoal Interdependency Graph)

Catalogues for each NFR


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Background

Classpects Leverage the advantage of both class

and aspects Improve the compositionality of aspect

modules

From 2-layered structure in AOP tohierarchical structure of n-layers

Aspects (now classpects) can advise otherclasspects


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public class SafetyRoomMalOI{SafetyRoomMal srm;public SafeRoomMalOI(SafeRoomMal srm){

this.srm = srm;}

public void safteyfun (){/* body of the method */

}before execution{public *

safeRoomMal.*(*))&& returns (ret) && args():call safetyFun();

}

Background

Classpects Example (in Eos-U, classpect implementation language)

Attribute: the classpectadvises SafetyRoomMal

ConstructorAdvise: now inside anamed method so that itcould be advised later if

necessary

Pointcut: now calls theadvise method


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FrameworkCreating SIG

Creating SIGynthesizing claspects (skeleton)

Discovering classes for claspects

Integrating NFR with FR

A SIG describing the NFR of the system

Classpects that implements the NFRs

Correspondence between the classpects thatdescribe NFR and classes that describe FR

Design document that captures both NFR and FR


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Creating Classpects from SIGA(B)

A1(B) A2(B)

Performance (Account)

Space (Account) Response Time (Account)

Space

Performance

Account

Response time

A classpect A is applied to the classpect B

Two classpects A1 and A2 are applied to classpect A1.


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Creating Classpects from SIG

A(B)

A(B1) A(B2)

Case 1: When B1 and B2 are subclasses of B

A classpect A is applied to the classpect B

The advice of A applies automatically to B1 and B2 sincethey are subclasses of B

2.

Case 2: When B1 and B2 applies to different attributesof B (decomposition via attributes) A classpect A is applied to the classpect B

A classpect A1 advises A about B1 and A2 advises A

about B2Case 3: When B doesnt exist in the functional

decomposition

A classpect A applies to B1 and B2


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Example

public class SafeRoomMal{

1 Room rm;2 public SafeRoomMal(Room rm){3 this.rm = rm;4 }5 public void safteyfun(){6 inform facility manager7 }8 before execution{(public *Room.*(*))9 && returns (ret) && args():10 call safetyFun();

}

Safety(Room.

Malfunction)

Safety(Room.

Malfunction.Motion Detector)

Safety(Room.

Malfunction.OI) inform facility manager

All ceiling lights on inform user set room as occupied


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ExampleSafety(Room.


Safety(Room.

Malfunction.OI)

All ceiling lights on

inform user

public class SafeRoomMalOI{

SafeRoomMal srm;/*CONSTRUCTOR*/public void safteyfun (){

all ceiling lights onand inform user

}/* POINTCUT*/}

Safety(Room.


inform user

set room as occupied

public class SafeRoomMalMD{SafeRoomMal srm;

/*CONSTRUCTOR*/public void safteyfun (){

inform userand set room as occupied

}

/* POINTCUT*/}


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ExampleObservation

The code is skeletalText information from the SIG

Need to incorporate info from functional analysis

Preserves the hierarchy in the SIG

SafeRoomMal advises Room

SafeRoomMalOI and SafeRoomMalMD adviseSafeRoomMal


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Discovering Classes To match the claspects with classes

Use the same vocabulary Unless NFR and FR analysis done by the same

person, not reliable

Account class may have different methods from NFRAND FR perspective

Use use-cases to find which classes may beaffected

Use the requirement document in such a way that Often the NFR is mentioned along with the class

that it applies to


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public class SafeRoomMalOI{

SafeRoomMal srm;/*CONSTRUCTOR*/public void safteyfun (){

all ceiling lights onand inform user

}/* POINTCUT*/}

Room class

Integration

public void safteyfun (){for all i in srm.rm.lights{srm.rm.turnOnLights(i);

}println (``This room"+ srm.rm.id+ ``has a malfunction");

}

+setLightIntensity()

+occupied() : boolean+setOccupied()+lightIntensity() : Byte+turnLights(in light : Single)+checkSafety() : bool

+id : Integer+lights : sequence(idl)+user : String+occupied : Boolean+fm : String+lightintensity : Byte

Roomm


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Use Cases and their Sequence

Diagrams from SIG

Class diagrams are useless without use

cases they participate in The use cases are the NFRs that we

identified in the SIG

Specifically, the interior nodes of the SIGthat havent been captured as classpects.


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Use Cases and their Sequence

Diagrams from SIG

Example (based on the previous example)

Hotel Room Notice

ALT

Reserve()

A=checkSafety()

|a=true|

|a=false| safety

PAR

S1 S2 S3

safety

FUNCTIONAL

NON-FUNCTIONAL


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Q-SIG: Quantified SIG Problems with SIG

Prioritization All NFRs are not equally important

In ATM application, confidentiality is more

important than accuracy which is more importantthan availability

Design Alternatives

As NFRs compete for resources, we need tofind the best set of design decisions to satisfyall NFRs


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Q-SIG: Quantified SIG Design alternatives in SIG are dealt with

the OR decompositionAuthenticate User Access

Use Pin Id/passwd Another ID

A B Result

D D D

D S S

S S S

D=denied

S=Satisfied

Partial OR decomposition

table


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Q-SIG: Quantified SIG

A

B

G

C

D FE

+

++

---

F and G are alternatives toimplement C.

F is better (++) than G (+) inimplementing C

F has a strong (--) conflict with Bthan G(-)

which one (F OR G) do you

choose to implement C?

NO clear guideline using NFR-Framework


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Q-SIG: Quantified SIG Solution for both priority problem and

trade-off problem in SIG QUANTIFICATION

It is the failure to represent different degrees ofsatisfibility and importance that is the root ofthe two problems.

The OR decomposition technique has to

be changed since it is useless for decidingamong alternatives.


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Q-SIG: Quantified SIG Solution (contd)

Downward arrows-

decomposition Upward arrows-design

alternatives AND decompostion-all must

add up to 1 The contribution of a child to

its parent is the value of thechild multiplied by the arrowvalue that connects them

The value of a node is thesum of the contribution fromeach child.

All leaf nodes have value 1

A

B

G

C

D FE

0.7

0.9

-0.6-0.90.5 0.5

0.3 0.7

The objective is to get thedesign alternatives that getthe highest value for the root


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Q-SIG: Quantified SIG How to decide between F and G

Ad-Hoc approach: Choose each and use itto calculate the value at A. F: 0.3*(1-0.9)+0.9*0.7=0.66

G:0.3*(1-0.6)+0.7*0.7=0.61 F is chosen

Because the left arm is not as important as theright arm

We cannot make this kind of decision based onSIG

Even then, the result is very close because ofthe trade-off


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Still F is chosen but with less calculation The gain may not be apparent because of the

simplicity of the example

Q-SIG: Quantified SIG

A

BC

F0.9

-0.9

0.3 0.7

A

B

G

C

0.7-0.6

0.3 0.7VS

F: -0.9*0.3 + 0.9* 0.7 = 0.36 G: -0.6*0.3 + 0.7* 0.7 = 0.31


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Conclusion Bridged the gap between requirement

analysis and implementation for NFRs Maintained separation of concerns

Ease of traciblity

NFRs are treated as first-class designelements Both FR and NFRs are implemented as

classpects, sequence diagrams, etc Proposed Q-SIG for addressing

Priority problem

Tradeoff problem

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