the oo design process1.mht

VC书籍介绍C++的应用的TheOODesignProcess.zip 电子书好用的

            the more heinous crimes perpetrated by Microsoft is the =
introduction=20
            of the verb "to architect" into English. Architects =
<I>design</I>=20
            buildings; they do not "architect" them. The reason I bring =
up this=20
            malapropism is that this specific abuse of the language =
artificially=20
            implies that a building's architect and a computer program's =

            architect are engaged in fundamentally different activities. =
I=20
            strongly believe that architecture is architecture, whether =
you're=20
            designing a building or whether you're designing software. =
For=20
            example, Christopher Alexander -- an architect of buildings =
--=20
            conceived the notion of a design pattern (see <I>A Pattern =
Language:=20
            Towns, Buildings, Construction</I> in <A=20
            =
href=3D"http://www-106.ibm.com/developerworks/library/oo-design1/index.ht=
ml#resources">Resources</A>)=20
            and design patterns are fundamental to contemporary software =

            architecture.</P>
            <P>If you were to walk up to a contractor and say, "I want =
you to=20
            build a house for me; how much will it cost, and when will =
you have=20
            it finished?" he'd look at you as if you were crazy. =
Programmers=20
            definitively answer equally vague questions all the time, =
however,=20
            and people wonder why software is rarely delivered on time =
and=20
            within budget. Moreover, no contractor would even consider =
starting=20
            construction on something as complex as a building without =
some sort=20
            of plan. Plans developed by contractors themselves will =
typically=20
            not yield as nice a building as those developed by =
architects,=20
            however. Contractors will naturally design for ease of =
construction=20
            and low cost, which are not necessarily the best choices for =
a=20
            building that you plan to live in. Programmers, similarly, =
are=20
            typically not the best equipped people for designing =
programs, since=20
            they have different priorities than the end user. This is =
not to say=20
            that a good architect won't know how to construct what he's=20
            designing -- I'm convinced that the best software architects =
are=20
            also the best programmers -- but that design and =
construction are=20
            different activities and need not be performed by the same=20
            people.</P>
            <P>The first step in designing a building is meeting with =
the client=20
            and figuring out how the building is going to be used. =
Architects=20
            are interested in the client's aesthetics, of course, but =
they ask=20
            many other questions. What are your hobbies? (Do you need=20
            specialized space for them?) Are there pets? (Do you want a=20
            cat-feeding station in the kitchen?) Do you have children? =
(Do they=20
            need a playroom?) How many? (How big should the playroom =
be?) All of=20
            these things influence the design of a building. If an =
activity=20
            that's going to be performed in the building is unfamiliar =
to the=20
            architect, then he or she will have to learn something about =
that=20
            activity to arrive at a satisfactory design. If the client =
is a koi=20
            keeper, for example, the architect is going to have to learn =
about=20
            pond technology -- not at the level of a koi keeper (a =
"domain=20
            expert" in design parlance), but at least at the level of a =
well=20
            informed layperson. Note that the emphasis is on how the =
building=20
            will be used. Construction considerations, though they're =
always in=20
            the back of the architect's mind and do influence the =
design, are=20
            not primary.</P>
            <P>The next step is to sketch potential buildings, rooms, =
grounds,=20
            and so forth. Lots of things change at this point -- rooms =
move=20
            around and change shape, fixtures and walls are added and =
removed.=20
            Only when the client's needs are correctly reflected by the =
sketches=20
            will a set of "final" plans be created, but even these plans =
aren't=20
            really final. They're submitted to contractors and =
engineers, all of=20
            whom request changes, all of which (if they're visible, at =
least, or=20
            affect cost or schedule) are run by the client. Only then =
does=20
            construction begin.</P>
            <P>The level of detail in the plans is also relevant. Much =
of the=20
            design work is done as the building is being constructed. =
The=20
            architect shows where the walls go, but the contractor =
figures out=20
            the details -- stud placement, framing for the windows and =
doors,=20
            and so on. The architect shows where the electrical outlets =
go, but=20
            the electrician figures out how to route the wires and where =
the=20
            electrical entrance goes. The plans show the drains and =
plumbing=20
            fixtures, but the plumber figures out how to route the pipes =
and=20
            hook up to the water main and sewer. That's not to say that =
these=20
            parts of the building aren't designed, but rather that this =
part of=20
            the design is done by the specialist who's doing the =
construction.=20
            This design work is often done informally -- on the site as =
work=20
            progresses. Moreover, most of the design artifacts, like =
scraps of=20
            paper with drawings on them or sketches made on studs inside =
the=20
            wall, are discarded because they aren't relevant after the =
object is=20
            built. When the specialist needs to do something that =
affects other=20
            specialists or the overall design of the building, then the =
ball is=20
            passed back to the architect, who modifies the master plans =
(after=20
            consulting the client).</P>
            <P>Given simple and complex ways to solve the same problem, =
the=20
            simple way is always used provided that it doesn't impact =
the=20
            integrity or aesthetics of the structure. Nonetheless, =
sometimes the=20
            only way to do something is complicated. It's also important =
to note=20
            that the level of detail required before construction begins =
is a=20
            function of the complexity of the structure. You can design =
a dog=20
            house on a napkin. A house requires more detail. In a =
skyscraper,=20
            virtually every pipe and electrical conduit is designed =
(though the=20
            positions of the walls sometimes aren't!).</P><A name=3D6>
            <P><STRONG class=3Dsubhead>Summing up</STRONG> <BR>The =
process I just=20
            described is essentially the same process that I use to =
create=20
            software, and it's that process that this column will =
demonstrate=20
            piece by piece. Starting next month, I'll go into lots of =
detail so=20
            that the detail can be put into context. Many of these =
operations=20
            actually occur in parallel, and we'll see that in upcoming =
months:=20
            <OL>
              <LI>Learn about the problem domain.=20
              <LI>Interview the users and determine their needs and =
goals.=20
              <LI>Develop the problem statement.=20
              <LI>Design the user interface.=20
              <LI>Develop the use cases.=20
              <LI>Rough out a draft static model.=20
              <LI>Develop the dynamic model while refining the static =
model.=20
              <LI>Implement. </LI></OL>
            <P></P>
            <P>As I go through these steps, I intend to capture the =
entire=20
            process as it occurs, including the mistakes I make and how =
I fix=20
            them. By the time we're finished, you'll have a complete =
(and=20
            realistic) picture of the design process.</P><A =
name=3Dresources>
            <P><STRONG class=3Dsubhead>Resources</STRONG>=20
            <UL>
              <LI>Check out <I><A=20
              =
href=3D"http://www.amazon.com/exec/obidos/ASIN/0201628783/alleiholuasso">=
Succeeding=20
              with Objects: Decision Frameworks for Project =
Management</A></I>=20
              by Adele Goldberg and Kenneth Rubin, a stunningly good =
book for=20
              managers who want to move their shops into an OO =
environment.=20
              <LI>RUP (the Rational Unified Process) is described by =
Ivar=20
              Jacobson, Grady Booch, and James Rumbaugh in <I><A=20
              =
href=3D"http://www.amazon.com/exec/obidos/ASIN/0201571692/alleiholuasso">=
The=20
              Unified Software Development Process</A></I>.=20
              <LI>XP (Extreme Programming) is described by Kent Beck in =
<I><A=20
              =
href=3D"http://www.amazon.com/exec/obidos/ASIN/0201616416/alleiholuasso">=
Extreme=20
              Programming Explained: Embrace Change</A></I>. XP is=20
              controversial, but I expect that a lot of the controversy =
comes=20
              from people making assumptions as to what Beck is talking =
about=20
              without having first read his book. XP and RUP actually =
integrate=20
              quite nicely, as described by Grady Booch in a draft =
chapter of=20
              his new OO-Design book, found at <A=20
              =
href=3D"http://www.objectmentor.com/publications/RUPvsXP.pdf">http://www.=
objectmentor.com/publications/RUPvsXP.pdf</A>=20
              (PDF). The <A=20
              =
href=3D"http://www.objectmentor.com/base.asp?id=3D40">ObjectMentor Web=20
              site</A> also has a wealth of useful material on this =
topic.=20
              <LI>You can get a copy of my UML templates for Visio from =
the=20
              Goodies section of <A href=3D"http://www.holub.com/">my =
Web=20
              site</A>.=20
              <LI>Read more about design and architecture in <I><A=20
              =
href=3D"http://www.amazon.com/exec/obidos/ASIN/0195019199/alleiholuasso">=
A=20
              Pattern Language: Towns, Buildings, Construction</A></I> =
by=20
              Christopher Alexander, Sara Ishikawa, and Murray=20
            Silverstein.</LI></UL><A name=3Dauthor>
            <P><STRONG class=3Dsubhead>About the author</STRONG> =
<BR><!-- <img SRC=3D"author.jpg" BORDER=3D0 width=3D64 height=3D71 =
align=3DLEFT> -->Allen=20
            Holub has been working in the computer industry since 1979. =
He is=20
            widely published in magazines (<I>Dr. Dobb's Journal</I>,=20
            <I>Programmers Journal</I>, <I>Byte</I>, <I>MSJ</I>, among =
others)=20
            and is a Contributing Editor to the online magazine <A=20
            href=3D"http://www.javaworld.com/">JavaWorld</A>. He has =
eight books=20
            to his credit, the latest of which (<A=20
            =
href=3D"http://www.amazon.com/exec/obidos/ASIN/1893115100/alleiholuasso">=
<I>Taming=20
            Java Threads</I></A>) covers the traps and pitfalls of Java=20
            threading. He's been designing and building object-oriented =
software=20
            for longer than he cares to remember. After eight years as a =
C++=20
            programmer, Allen abandoned C++ for Java programming in =
early 1996.=20
            He's been teaching programming (first C, then C++ and MFC, =
now=20
            OO-Design and Java programming) both on his own and for the=20
            University of California Berkeley Extension since 1982. =
Allen offers=20
            both public classes and in-house training in Java technology =
and=20
            object-oriented design topics. He also does object-oriented =
design=20
            consulting and contract Java programming. Visit Allen's Web =
site at=20
            <A =
href=3D"http://www.holub.com/">http://www.holub.com/</A>.</P><!-- End =
paper --><BR></TD>
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