Software Metrics Lec011

7/29/2019 Software Metrics Lec011

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Software Metrics (SEN-630)Master of

Software Engineering

Dr. Syed Asif AliHead of Computer Science

Department Bahria University


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Quality Model

product

operation revision transition

reliability efficiency usability maintainability testability portability reusability

Metrics


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High level Design Metrics

Structural Complexity

Data Complexity

System Complexity

Card & Glass 80

Structural Complexity S(i) of a module i.

S(i) = fout2(i)

Fan out is the number of modules immediately

subordinate (directly invoked).


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Design Metrics

Data Complexity D(i)

D(i) = v(i)/[fout(i)+1]

v(i) is the number of inputs and outputs

passed to and from i

System Complexity C(i)

C(i) = S(i) + D(i)As each increases the overall complexity of

the architecture increases


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System Complexity Metric

Another metric:

length(i) * [fin(i) + fout(i)]2

Length is LOC

Fan in is the number of modules that invoke i

Graph based:

Nodes + edges Modules + lines of control

Depth of tree, arc to node ratio


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Coupling

Data and control flow di input data parameters

ci input control parameters

do output data parameters

co output control parameters

Global gd global variables for data

gc global variables for control

Environmental w fan in

r fan out


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Metrics for Coupling

Mc = k/m, k=1

m = di + aci + do + bco + gd + cgc + w + r

a, b, c, k can be adjusted based on actual

data


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Component Level Metrics

Cohesion (internal interaction) - a function of dataobjects

Coupling (external interaction) - a function of input and

output parameters, global variables, and modules called

Complexity of program flow - hundreds have beenproposed (e.g., cyclomatic complexity)

Cohesion difficult to measure Bieman 94, TSE 20(8)


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Using Metrics

The Process Select appropriate metrics for problem

Utilized metrics on problem

Assessment and feedback

Formulate

Collect

Analysis Interpretation

Feedback


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Metrics for the Object Oriented

Chidamber & Kemerer 94 TSE 20(6)

Metrics specifically designed to addressobject oriented software

Class oriented metrics

Direct measures


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Weighted Methods per Class

WMC =

ci is the complexity (e.g., volume, cyclomaticcomplexity, etc.) of each method

Viewpoints: (of Chidamber and Kemerer)

-The number of methods and complexity of methods is an indicator

ofhow much t ime and effor t is required to develop andmaintainthe object

-The larger the number of methodsin an object, the greater thepotentialimpact on the chi ldren

-Objects with large number of methodsare likely to be more

application specific, l imit ing the poss ible reuse

n

i

ic1


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Depth of Inheritance Tree

DIT is the maximum length from a node to

the root (base class)

Viewpoints: Lower level subclasses inherit a number of methods

making behavior harder to predict

Deeper trees indicate greater design complexity


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Number of Children

NOC is the number of subclasses immediatelysubordinate to a class

Viewpoints: As NOC grows, reuse increases - but the abstraction may be diluted

Depth is generally betterthan breadth in class hierarchy, since itpromotes reuse of methods through inheritance

Classes higher up in the hierarchyshould have more sub-classesthen those lower down

NOC gives an idea of the potential influence a class has on thedesign: classes with large number of children may require moretesting


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Coupling between Classes

CBO is the number of collaborations

between two classes (fan-out of a class C) the number of other classes that are referenced in the

class C (a reference to another class, A, is anreference to a method or a data member of class A)

Viewpoints: As collaboration increases reuse decreases

High fan-outs represent class coupling to other classes/objects and

thus are undesirable

High fan-ins represent good object designs and high level of reuse

Not possible to maintain high fan-in and low fan outs across the

entire system


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Response for a Class

RFC is the number of methods that could be

called in response to a message to a class (local

+ remote)

Viewpoints:

As RFC increases

testing effort increases greater the complexity of the object

harder it is to understand


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Lack of Cohesion in Methods

LCOM poorly described in Pressman

Class Ckwith n methods M1,Mn

Ij is the set of instance variables used by

Mj


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LCOM

There are n such sets I1,, In

P= {(Ii, Ij) | (IiIj) = }

Q = {(Ii, Ij) | (IiIj) }

If all n sets Iiare then P=

LCOM = |P| - |Q|, if |P| > |Q| LCOM = 0 otherwise


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Example LCOM

Take class Cwith M1, M2, M3 I1 = {a, b, c, d, e}

I2= {a, b, e}

I3 = {x, y, z}

P= {(I1, I3), (I2, I3)}

Q = {(I1, I2)}

Thus LCOM = 1


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Explanation

LCOM is the number of empty intersectionsminus the number of non-empty intersections

This is a notion of degree of similarity ofmethods

If two methods use common instance variablesthen they are similar

LCOM of zero is not maximally cohesive

|P| = |Q| or |P| < |Q|


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Class Size

CS

Total number of operations (inherited, private,

public)

Number of attributes (inherited, private,

public)

May be an indication of too muchresponsibility for a class


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Number of Operations Overridden

NOO

A large number for NOO indicatespossible problems with the design

Poor abstraction in inheritance hierarchy


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Number of Operations Added

NOA

The number of operations added by asubclass

As operations are added it is farther away

from super class As depth increases NOA should decrease


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Method Inheritance Factor

MIF = .

Mi(Ci) is the number of methods inheritedand not overridden in Ci

Ma(Ci) is the number of methods that can

be invoked with Ci Md(Ci) is the number of methods declared

in Ci

n

i

ia

n

i

ii

CM

CM

1

1

)(

)(


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MIF

Ma(Ci) = Md(Ci) + Mi(Ci)

All that can be invoked = new or

overloaded + things inherited

MIF is [0,1]

MIF near 1 means little specialization MIF near 0 means large change


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Coupling Factor

CF= .

is_client(x,y) = 1 iff a relationship exists betweenthe client class and the server class. 0otherwise

(TC2-TC) is the total number of relationshipspossible

CF is [0,1] with 1 meaning high coupling

)(

),(_2 TCTC

CCclientisi j ji


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Polymorphism Factor

PF = .

Mn() is the number of new methods

Mo() is the number of overriding methods

DC() number of descendent classes of a base class

The number of methods that redefines inherited methods, divided bymaximum number of possible distinct polymorphic situations

i iin

i io

CDCCM

CM

)()(

)(


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Operational Oriented Metrics

Average operation size (LOC, volume)

Number of messages sent by an operator

Operation complexity cyclomatic

Average number of parameters/operation Larger the number the more complex the

collaboration


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Encapsulation

Lack of cohesion

Percent public and protected

Public access to data members


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Inheritance

Number of root classes

Fan in multiple inheritance

Software Metrics Lec011

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