面向对象设计的度量体系：提升软件开发管理效率

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面向对象设计(A Metrics Suite for Object-Oriented Design)是软件工程领域的一项重要研究，它在IEEE Transactions on Software Engineering, Vol.20, No.6, June 1994期刊上发表。Shyam R. Chidamber和Chris F. Kemerer两位作者提出了这一套度量标准，以满足当时日益增长的软件开发过程中过程改进的需求。随着信息技术的广泛应用，特别是随着面向对象（Object-Oriented, OOD）技术的兴起，管理者对于软件开发过程的管理和评估变得更加迫切。传统的软件开发方法论面临着挑战，因为新的技术引入往往缺乏成熟的实践标准。因此，这套新的度量体系旨在解决这个问题，通过开发一套针对OO设计的量化指标，帮助组织更好地理解和管理基于OO的设计过程。在此之前的研究虽然在理解软件开发流程方面有所贡献，但受到了批评，例如指标的有效性、实用性以及是否能准确反映设计质量等问题。 Chidamber和Kemerer的《面向对象设计度量》套装包括了一系列关键的度量指标，如类的复杂性（如类的大小、扇入/扇出、深度等）、模块化度、耦合性和内聚性等，这些度量有助于评估设计的可读性、可维护性和可扩展性。它们不仅提供了量化分析的角度，还试图减少主观评价的不确定性，以便决策者能够基于数据驱动的方式来优化设计和项目管理。然而，值得注意的是，这套度量并非一蹴而就的解决方案，其有效性在实践中需要不断验证和完善。实施过程中可能遇到的挑战包括如何选择合适的度量、如何收集和解释数据、以及如何将这些度量融入到日常开发流程中，使之成为持续改进的工具。此外，度量结果的解读和应用也需要结合具体项目的特点和团队的实际经验。《A Metrics Suite for Object-Oriented Design》为软件开发过程中的面向对象设计提供了重要的量化框架，但同时也提示我们，任何度量都需要与实际开发环境相结合，并持续优化，以确保其在指导实践中的有效性和价值。

CHIDAMBER AND KEMERER:

METRICS

SUITE

FOR

OBJECT

ORIENTED DESIGN

419

inherently. An observer can assign features to an individual,

but these are attributes and not properties. All substantial

individuals possess a finite set of properties; as Bunge notes,

“there are no bare individuals except in our imagination” [5].

Some of the attributes of an individual will reflect its

properties. Indeed, properties are recognized only through

attributes. A known property must have at least one attribute

representing it. Properties do not exist on their own, but are

“attached” to individuals.

the other hand, individuals are

not simply bundles of properties. A substantial individual

and its properties collectively constitute an

object

[42], [43].

Therefore, an object is not simply a bundle of methods,

but a representation of the application domain that includes

the methods and instance variables that a designer assigns

to that object. Another benefit of this stream of research is

that it provides a formal mathematical approach to dealing

specifically with the key ideas of object orientation.

An object can be represented in the following manner:

(~,p(z))

where

is the substantial iniividual and

p(z)

is the finite collection of its properties.

:I:

can be considered to be the token

name by which

the object is represented in a system.

object oriented

terminology, the instance variables’ together with its methods4

are the properties of the object

[l].

Using these representations of objects, previous research has

defined concepts like scope and similarity that are relevant to

object oriented systems [5], [42]. Following this tradition, this

paper defines in the paragraphs below two important software

design concepts for object classes, coupling and cohesion.

Intuitively, coupling refers to the degree of interdependence

between parts of a design, while cohesion refers to the internal

consistency within parts of the design. All other things being

equal, good software design practice calls for minimizing

coupling and maximizing cohesiveness. It should be noted that

these definitions are derived from the ontology of objects as

opposed to other sources that have been graph-theory (e.g.,

McCabe [29]), information content (e.g., Halstead

[

171) or

structural attributes (e.g., Card and Agresti [7]).

For

further

details on the appropriateness of the ontological approach the

reader is referred to the comprehensive treatment of the subject

in [42], [321 and [391.

Coupling

ontological terms, “two objects are coupled if

and only if at least one of them acts upon the other,

is said

to act upon

if the history of

is affected by

where

history is defined as the chronologically ordered states that a

thing traverses in time” [41, p. 5471.

Let

(z,p(z))

and

E’

(y,p(y))

be two objects.

‘An instance variable stores a unique value in each instance

class

method is an operation on an object that

defined as part

the

declaration

the class.

where

{M,}

is the set of methods and

{It}

is the set of instance

variables of object

Using the above definition of coupling, any action by

{M-y}

{My}

{ly}

constitutes coupling, as does any action by

{My}

{M*y}

{I-y}.

When

A4-y

calls

My,

Mdy

alters

the history of the usage of

My;

similarly when

May

uses

I,,

it alters the access and usage history of

11,.

Therefore, any

evidence of a method of one object using methods or instance

variables of another object constitutes coupling. Since objects

of the same class have the same properties, two classes are

coupled when methods declared in one class use methods

instance variables of the other class.5

Cohesion

Bunge defines

similarity

IT()

of two things to be the

intersection of the sets of properties of the two things [5, p 871:

Following this general principle of defining similarity in terms

of sets, the degree of similarity of the methods within the

object can be defined

be the intersection of the sets of

instance variables that are used by the methods. This is an

extension of Bunge’s definition of similarity to similarity of

methods. It should be clearly understood that instance variables

are not properties of methods, but it is consistent with the

notion that methods of an object are intimately connected to

its instance variables.

where

u(M1.

M2)

degree of similarity of methods

and

{Ii}

set of instance variables used by method

M,.

Example:

Let

{II}

{a,b,c,d,e}

and

(12)

{n,b,e}.

(11)

{I2}

is nonempty, and

CT(MI,M~)

{a,b,e}.

The degree of similarity of methods relates both to the

conventional notion of cohesion in software engineering, (i.e.,

keeping related things together) as well as encapsulation, that

is, the bundling of methods and instance variables in an object

class. The

degree

similarity

of methods can be viewed as

a major aspect of object class cohesiveness. If an object class

has different methods performing different operations on the

same set of instance variables, the class is cohesive. This view

of cohesion is centered

data that is encapsulated within an

object and

how methods interact with data. It is proposed

for object orientation as an alternative to other previous

approaches, such as generalization-specialization cohesion or

service cohesion as defined by Coad and Yourdon

[

111.

Complexity

an Object:

Bunge defines complexity of an

individual to be the “numerosity of its composition”, implying

that a complex individual has a large number

properties

(51. Using this definition as a base, the complexity of an object

class can be defined to be the cardinality of its set of properties.

Complexity of

(z,p(z))

lp(z)I,

where

lp(z)I

is the cardi-

nality

p(z).

Scope

Properties:

simple terms, a class

a set of

objects that have common properties (i.e., methods and in-

stance variables). A designer develops an abstraction of the

’

Note that this will include coupling due to inheritance.

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