软件开发概念和设计方法大学毕业论文外文文献翻译及原文

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翻译日期： 2017.02.14

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Software Development Concepts and Design

Methodologies

During the 1960s, ma inframes and higher level programming languages were applied to man y problems including human resource s yste ms,reservation s yste ms, and manufacturing s yste ms. Computers and software were seen as the cure all for man y bu siness issues were some times applied blindly. S yste ms sometimes failed to solve the problem for which the y were designed for man y reasons including:

?Inability to sufficiently understand complex problems

?Not sufficiently taking into account end-u ser needs, the organizational environ ment, and performance tradeoffs

?Inability to accurately estimate development time and operational costs ?Lack of framework for consistent and regular customer communications At this time, the concept of structured programming, top-down design, stepwise refinement，and modularity e merged. Structured programming is still the most dominant approach to software engineering and is still evo lving. These failures led to the concept of "software engineering" based upon the idea that an engineering-like discipl ine could be applied to software design and develop ment.

Software design is a process where the software designer applies techniques and principles to produce a conceptual model that de scribes and defines a solution to a problem. In the beginning, this des ign process has not been well structured and the model does not alwa ys accurately represent the problem of software development. However,design methodologies have been evolving to accommo date changes in technolog y coupled with our increased understanding of development processes.

Whereas early desig n methods addressed specific aspects of the

develop ment process, current methods atte mpt to address the entire scope of software development. Software design methods are often classified in reference to the peri od in which the y were introduced and the problems at that time. Driven b y coding and testing problems, tools and methods were developed. Early methods focused on modularity a nd top-down development, and information hiding through abstraction. This led to t he development of structured languages, structured analysis, and data flow analysis.

In the last decade or so, the expense involved in automation has shifted from hardware to people. Therefore, the software engineering community has been focused on object oriented (O-O) design and the concept of re-usable code in order to reduce the human cost component. Inefficient designs and develop ment methodologies have been addressed with Computer Aided Software Engineering (CASE) tools, and fourth generation design l anguages. This has been done in an attempt replace the traditional waterf all life c ycle process model under which most existing software has been developed.

一、Software Design Fundamentals

Software design meth ods all aim to provide the software designer wi th a s yste m blueprint. This blueprint usually has three aspects: data, architectural, and procedural.

?Data design refers to the data's organization, relationships, access and processing methods.

?Architectural design defines the components of the sys tem a nd their relationships.

?Procedural design builds on the data and architectural design phases to describe the processing details of the s yste m.

Even though there are numerous design methodologies, their basic concepts are ver y similar-All software design methods partition the problem and software into smaller pieces in order to reduce complexity. They all strive to identif y data structures and functions, and provide measur ements for software quality. Some of the common principles in software design include: stepwise refinement, s oftware architecture, program structure, data structure,

software procedures, mo d u la r i t y,a b s tr a c t io n,a n d in f o r ma t io n h i d i n g.

二、M o d e r n D e s i g n M e t h o d o l o g i e s

C o n ve n t io n a l s o f t wa r e d e ve l o p me n t p r a c t ic e s c a n g e n e r a l l y b e

ma p p e d o n to t h e tr a d i t io n a l l i f e-c y c l e p h a s e s o f a n a l ys i s,f u n c t i o n a l

s p e c i f i c a t i o n,d e s i g n,i mp l e me n t a t i o n,t e s t i n g,a n d m a i n t e n a n c e.T h i s

t h o u g h t p r o c e s s i s i n a d e q u a t e f o r t o d a y's c o m p l e x i n f o r m a t i o n s y s t e m s.As the demand for software is growing much faster than the number of developers, adhering to conventional techniques such as the waterfall method requires too much time, too many people, and is difficult to ma nage. Hence, many new software development technologies have arisen. N e wl y d e ve lo p e d p r a c tic e s a n d mo d e ls d o n o t a tte mp t to s e p a r a te p h a s e s o f s o f twa r e development, such as specification and implementation, but instead focus on the concept of program transformation through stepwise refinement and iteration.

1、O b j e c t-O r i e n t e d Te c h n o l o g y

Object-Oriented (O-O) software design technology is fundamentally different from the traditional methods described above. With traditional methods, each module is recognized a major step in the overall process and the process goes from one step to the next. On the other hand, O-O design is structured around a model of objects and the functions they perform.

O-O programming can be traced to the simulation language SIMULA, a hig h level language developed in the late 60's that introduced object classes as a method to encapsulate data. Later, in the 1970s, Smalltalk was introduced as a complete grapgh design and coding as detail is added to the design. This provides a common language throughout each stage in development. O-O is best applied with specifically designed O-O development tools, but it is important to remember that as a methodology is it not specific to any programming language. Many different programming languages can be used to implement 0-0 technology and design methodologies.

Instead of procedures and functions passing data back and forth, in object oriented design, the system is viewed as a collection of objects with messages passed from object to object. Each object has its own set of associated operations.

Object-oriented design is based on the idea of information hiding and modularization of both data and processing. It is best used when neither data structure nor processing operations are well defined ahead of time. This is quite useful in today's business environment where requirements are always changing and not very well defined. Thus, it has become quite popular! The concept of objects performing services is a natural way of thinking for both developers and customers. This facilitates understanding the problem domain and a more natural design. In addition, there are many benefits of object-oriented development. These include:

?I n h e r i t a n c e c a p i t a l i z e s o n t h e c o m m o n a l t y o f a t t r i b u t e s a n d s e r v i c e s a l l o w i n g c o d e a n d objects to be re-used.

.I n f o r m a t i o n h i d i n g m a k e s s y s t e m s m o r e s t a b l e b y l o c a l i z i n g c h a n g e s t o o b j e c t s a n d t h e r e b y m a k i n g t h e m r e u s a b l e.

.T h e o b j e c t-o r i e n t e d d e v e l o p m e n t p r o c e s s i s c o n s i s t e n t f r o m a n a l y s i s,t h r o u g h d e s i g n, t o c o d i n g.

More information on Object Oriented Programming principles can be found in Chapter 4-Organization of Programming Languages and Programming Concepts.

2、P r o t o t y p i n g

Prototyping was invented because end users participating in the development phase found it difficult to understand requirement specifications and conceptual models. However, when it first began being used in the 1980s, most conventional life c ycle developers considered it expensive and time consuming.

S i n c e t h a t t i m e,u s e r s a n d d e v e l o p e r s h a v e u s e d p r o t o t y p e s s u c c e s s f u l l y a s a communications tool to demonstrate system requirements. After several prototype iterations, developers have a better understanding of user requirements and users have a better idea of how the system will eventually work, look, and l.

T h e n u mb e r o f t i me s th e p r o to t yp e is in c r e me n t a l l y r e f in e d d e p e n d s o n h o w we l l th e u s e r r e q u i r e me n ts a n d u n d e r s t o o d.I t a ls o d e p e n d s o n th e u s e r s n e e d to a d d r e q u ir e me n ts o r c h a n g e p r e v i o u s l y s t a t e d r e q u i r e m e n t s.A f t e r

e s t a b l i s h i n g a n o v e r a l l a r c h i t e c t u r e a n d

f r a me w o r k, t h e s ys t e m i s d e v e l o p e d a n d d e l i v e r e d in in c r e me n ts.U s e r s ma y e x p e r i me n t w i t h a n d u s e d e l i v e r e d i n c r e me n t s w h i l e o t h e r s a r e b e i n

g d e v e l o p e d.Fo r i n s t a n c e,t

h e f

i r s t p r o t o t yp e ma y b e d e l i v e r e d t h a t i m p l e m e n t s a c e r t a i n s c r e e n w i t h o n l y s o m e a c t i v e m e n u i t e m s.W h i l e u s e r s a r e e x p e r i me n t i n g w i t h t h i s s c r e e n a n d me n u i t e ms,o t h e r s c r e e n s a n d me n u i t e ms a r e c o n c u r r e n t l y b e in g

d e v e l o p e d wh i c h la t e r w il l b e c o mb in e d w i th th e e x is t in g p r o to t yp e a s it

e vo l v e s.

O n c e t h e u s e r i s s a t i s f i e d t h a t t h e p r o t o t y p e m e e t s r e q u i r e m e n t s,t h e p r o t o t y p e i s t r a n s f o r me d i n to th e"s ys t e m".T h i s e ff o r t d e p e n d s o n s e v e r a l f a c to r s. I t ma y i n c lu d e a d d i n g f u n c t i o n a l i t y t h a t w a s n't i n i t i a l l y r e c o g n i z e d a s r e q u i r e d,r e p l a c i n g i n e f f i c i e n t p a r t s o f t h e p r o t o t yp e t o me e t p e r f o r ma n c e c r i t e r i a,o r a d a p t i n g t h e p r o t o t yp e t o f i t t h e u s e r's h a r d w a r e e n vi r o n me n t.

P r o t o t y p i n g c a n b e g i n v e r y e a r l y, a f t e r s o m e p r e l i m i n a r y r e q u i r e m e n t s a n a l y s i s h a s d e t e r m i n e d t h e b a s i c f u n c t i o n a l i t y,s c o p e,a n d e n v i r o n m e n t o f t h e p r o p o s e d s o f t w a r e.C o n t r a r y t o t h e t r a d i t i o n a l w a t e r f a l l me t h o d,i n t h e p r o t o t yp i n g,f u n c t i o n a l s p e c i f i c a t i o n s a r e n o t f i x e d.R a t h e r,u s e r s a r e e n c o u r a g e d t o m o d i f y t h e i r r e q u i r e m e n t s a s t h e y t h e m s e l v e s b e g i n t o u n d e r s t a n d t h e m b e t t e r.T h i s i s b e c a u s e u s e r s o f t e n d o n't r e a l l y k n o w w h a t t h e y w a n t u n t i l t h e y s e e i t o n t h e s c r e e n.T h e p r o t o t yp i n g p r o c e s s o f d e mo n s t r a t i o n,r e v i e w,a n d r e f i n e me n t g e t s t h e u s e r m o r e i n v o l v e d i n t h e d e v e l o p m e n t p r o c e s s,g i v i n g t h e m a s e n s e o f o w n e r s h i p d u r i n g t h e p r o c e s s a n d a t f i n a l s y s t e m d e l i v e r y.H o w e v e r,d u e t o t h e m i n d s e t o f"p r o t o t y p e", u s e r s o f t e n f in d i t d iff ic u l t to ve r if y t h a t th e p r o to t yp e s a tis f ie s th e ir r e q u ir e me n ts. T h e r e f o r e, g u id e l in e s mu s t b e e s t a b l i s h e d t o d e te r m in e wh e n t o s to p i te r a t in g a n d th e p r o to t yp e to f in a l p r o d u c t.