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diff --git a/js/games/nluqo.github.io/~bh/v3ch0/preface.html b/js/games/nluqo.github.io/~bh/v3ch0/preface.html new file mode 100644 index 0000000..6c6aace --- /dev/null +++ b/js/games/nluqo.github.io/~bh/v3ch0/preface.html @@ -0,0 +1,390 @@ +<HTML> +<HEAD> +<TITLE>Computer Science Logo Style vol 3:Preface</TITLE> +</HEAD> +<BODY> +<CITE>Computer Science Logo Style</CITE> volume 3: +<CITE>Beyond Programming</CITE> 2/e Copyright (C) 1997 MIT +<H1>Preface</H1> + +<TABLE width="100%"><TR><TD> +<IMG SRC="../csls3.jpg" ALT="cover photo"> +<TD><TABLE> +<TR><TD align="right"><CITE><A HREF="http://www.cs.berkeley.edu/~bh/">Brian +Harvey</A><BR>University of California, Berkeley</CITE> +<TR><TD align="right"><BR> +<TR><TD align="right"><A HREF="../pdf/v3ch00.pdf">Download PDF version</A> +<TR><TD align="right"><A HREF="../v3-toc2.html">Back to Table of Contents</A> +<TR><TD align="right">[no back] +chapter thread <A HREF="ack.html"><STRONG>NEXT</STRONG></A> +<TR><TD align="right"><A HREF="https://mitpress.mit.edu/books/computer-science-logo-style-second-edition-volume-3">MIT +Press web page for <CITE>Computer Science Logo Style</CITE></A> +</TABLE></TABLE> + +<HR> + +<P>The phrase "computer science" is still, in some circles, battling for +acceptance. Some people, not necessarily antagonistic to computers, consider +it an illegitimate merger of two disconnected ideas (much as I feel myself +about the phrase "computer literacy"). They don't see where the <EM> +science</EM> comes in; what is taught in computer science departments is mostly +how-to tricks of the trade, comparable to medical or legal training. Such +training is valuable to the individual and to society, but the trainees are +not learning to be scientists. + +<P> + +My own feeling is that there is some truth on both sides. There <EM>is</EM> +some science in computer science. Abelson and Sussman, in <EM>Structure +and Interpretation of Computer Programs,</EM> use the words "complexity" and +"process" to explain what it is that computer scientists study. A process +need not take place inside a computer, but it happens that computer processes +are particularly amenable to formal study and they shed light on the idea of +process in general. On the other hand, Abelson and Sussman are exceptional. +A great deal of what is called computer science <EM>is</EM> much more a +matter of programming techniques; many computer science students are first +offered courses in several different programming languages and then taught +specific techniques for particular problem domains, like graphics or data +base systems or compiler construction. And many students who find +themselves in computer science departments because they love programming +computers are impatient with theory and weak in mathematical +sophistication. Such students are perfectly satisfied with the how-to +approach. (I don't mean this as an insult. I have in mind some excellent +students I've taught who are brilliant programmers, very intelligent people, +but happen not to have a theoretical bent.) + +<P>My goal in this book is to provide a bridge over which a lover of practical +programming can cross into the world of theory. I envision someone who got +bored or confused early in the high school math curriculum and was left with +a distaste for formal thinking, but who is nevertheless a closet formalist +when programming, getting the same joy from representing an intellectual +problem in executable form that a traditional mathematician gets from +representing a similar problem in an axiom system. I've tried to discuss +the concerns of more abstract computer science using the language of concrete +Logo programs that embody those concerns. This is an ambitious goal and I'm +not sure how well I've succeeded. + +<P> + +For example, in automata theory there is an elementary result called +Kleene's Theorem that establishes the equivalence of two different +representations for a certain class of problems. One representation, the +finite-state machine, is a <EM>procedural</EM> one, a sequence of steps, like +a Pascal program. The other, the regular expression, is <EM>declarative,</EM> +describing the desired result rather than the sequence of steps needed to +get there, like a Prolog program. The representations are equivalent in the +sense that any problem that can be described as a regular expression can be +solved by a finite-state machine, and vice versa. (Not all problems are in +this category.) Automata theory texts offer a formal proof of Kleene's +Theorem using mathematical induction. What I offer is a Logo program that +takes a regular expression as input and actually works out an equivalent +finite-state machine for that particular expression. The program and the +formal proof are similar in structure, embodying many of the same ideas. +But the program is concrete and manipulable.<SUP>*</SUP> + +<P><SMALL><BLOCKQUOTE><SMALL><SUP>*</SUP>Of course, computer +programs are not concrete for everyone. Despite what I said above about +students who like programming but don't like abstraction, anyone who has +learned to see programs as concrete objects is well on the way to mastering +mathematical abstraction too; that's what gives me hope about this +enterprise. The fact that the Piagetian +boundary between concrete objects and +abstract ideas is not the same for everyone, and that what was formerly +abstract can become concrete in a suitable learning environment (such as +the one made possible by computers), was the insight that led +Seymour Papert +to espouse computer programming as an activity for children.</SMALL></BLOCKQUOTE></SMALL><P>Don't get the impression that the book contains nothing but formal +mathematics, even in executable guise. The first two chapters (on automata +theory and discrete mathematics) concern relatively abstract topics, although +each has practical applications; the later chapters are more directly about +the process of computer programming. + +<P><H2>About This Series</H2> + +<P>The book you are reading is the final volume in a three-volume series, +<EM>Computer Science Logo Style.</EM> +In the introductions to the earlier volumes I have distinguished two +approaches to computer science: the software engineering approach and the +artificial intelligence approach. The former makes the idea of <EM> +algorithm</EM> the central one. It thrives in a context of well-defined +problems; a computer program proposed as a solution to such a problem can +be clearly judged correct or incorrect, and it can be more or less efficient +than some other proposed solution. The artificial intelligence approach is +harder to describe in one sentence. It embraces vaguely defined problems; +it emphasizes an interactive process in which the programmer and the +computer are participants. + +<P>Of course the terms in which I describe the two approaches are not +value-free. A software engineer would use different language. Nor would +all experts necessarily accept my dichotomy in the first place. Alan Perlis + +says, in his foreword to <EM>Structure and Interpretation,</EM> "After all, +the critical programming concerns of software engineering and artificial +intelligence tend to coalesce as the systems under investigation become +larger. This explains why there is such growing interest in Lisp outside of +artificial intelligence." + +<P>I have also described the sequence of stages through which I think an +apprentice programmer travels. Volume 1 of this series, <EM>Symbolic +Computing,</EM> teaches the rules of the game. It is addressed to a reader +who has probably done some computer programming before, but is just starting +to get serious about it. It differs from most introductory Logo programming +books in that the latter focus attention on a particular programming goal, +usually turtle graphics, and try to make the language itself as transparent +as possible. I prefer to make the rules of the language an explicit object +of study, since the design of any language embodies the designer's ideas +about the structure of computer science. + +<P>Volume 2, <EM>Advanced Techniques,</EM> combines additional tutorial chapters +about advanced Logo features with a collection of more or less practical +programming projects. As in any field, apprentices learn by doing more than +they learn by reading books; yet they require the attention of a master to +see that they are learning a good style of work and not practicing bad +habits. To speak of apprenticeship in this century sounds quaint, and +in fact most of our master programmers do not take on apprentices. That's a +pity, I think; too many would-be apprentices don't find suitable guidance. +(They sometimes try to fill the gap by learning how to break into some +company's computer, and then they get in trouble.) No book can be as good +as living contact with a master programmer, but Volume 2 is my attempt. + +<P>This volume, <EM>Beyond Programming,</EM> is for the reader with a few substantial +programming projects, or more than a few, behind him or her, who is starting +to feel bored with programming for its own sake but isn't sure what to do +instead. Some people never do experience that sense of constriction, and +that's okay, as I said earlier. But I love mathematics myself, and I confess +that I'm always a little disappointed if one of my best students doesn't +come to share that love. In this volume my goal is to tempt them. + +<P> +<H2>How to Read This Book</H2> + +<P>Slowly. + +<P>Each chapter introduces some rather sophisticated ideas. You may find that +reading the chapter once leaves you with only a vague understanding. There +are two things you can do about that: Read it again and experiment with the +programs in the chapter. Test the limits of the programs; see what problems +you can solve that are similar to the ones I solve, and what problems don't +yield to the techniques I use. Think about how you could extend the +techniques. You should understand how each program works, but don't fall +into the trap of thinking that the program is the most important thing in +the chapter. You should also understand how the program fits into a broader +theoretical framework--how it embodies the <EM>ideas</EM> of the chapter. + +<P>The programs in each chapter are available over the +Internet along with Berkeley Logo, a free Logo interpreter that runs on PC, +Macintosh, and Unix systems. Please note, though, that in a few places I +show alternate versions of a program in the text. In those situations the +online file contains the final version, but it's worth your while to work +through the development of the program by typing in the earlier versions +yourself. (I don't do this with enormous programs.) + +<P>Most of the chapters concentrate on a single idea selected from a broad +topic. Earlier I mentioned Kleene's Theorem as an example; that theorem is +a very small piece of automata theory, but it takes up the bulk of the +chapter. Only in the final pages do I hint at some of the other topics +within automata theory. I think it's better to teach you one idea in depth +than to give a handwavy picture of an entire area of study. You should +expect to have to explore each area further by reading books about that +topic; this book ends with a bibliography to help you. + +<P>The specific ideas I present are generally not at the cutting edge of +current research in computer science; instead, they are older, more +fundamental ideas. In part this is inherent in the introductory nature of +the book. In part it reflects the limitations of my own knowledge. And in +part it reflects the limitations of the home computers I expect my readers +to have available to them. Then, sometimes the older ideas are easier to +present in a complete, coherent, concrete form. For example, in the chapter +on artificial intelligence I present an implementation of a program from +1964. In that program, the method used in the understanding of English +sentences is closely connected to the particular problem (solving algebra +word problems) that that program handles. A more modern English sentence +parsing program is not only slower and more complicated but also is hard to +demonstrate unless it's attached to an equally slow and complicated expert +system or other purposeful program. I hint about the newer techniques, but +I don't demonstrate them. + +<P>Chapters make occasional references to earlier chapters, so it's best if you +read the book in order, although the references are rarely so substantial +that you can't survive skipping a chapter. (But definitely read Chapter 4 +before Chapter 5.) + +<P><H2>What Isn't Included</H2> + +<P>When I first conceived of this series I described the third volume as "the +first chapter of every graduate computer science course." As it turned out, +the actual book does not pretend to cover anything like the entire field of +computer science. It contains a selection of topics that I know about and +find most worthwhile. + +<P>Some topics are omitted because I just don't care about them personally. +For example, I don't have anything to say about numerical analysis. I'm +glad there are people in the world who are concerned to ensure that when I +use the square root primitive in Logo I get the right answer, but I am not +such a person myself. That doesn't mean you have to share my taste, but if +you want to know about numerical analysis you'll have to read someone else's +book. + +<P>Other topics are omitted because I couldn't find any way to illustrate the +topic through Logo programming on a microcomputer, which was one of the +constraints I set for myself in planning this series. For example, one of +the areas of computer science I find <EM>most</EM> interesting is +operating systems. My +high school students in Sudbury had access to a Unix timesharing +system on a minicomputer and they did significant software development in +that environment. But I don't know how to make that particular experience +available on a single-user microcomputer in which the operating system is +someone's trade secret. + +<P>Finally, some topics just didn't fit. I originally planned to have a +chapter on graphics programming, but I decided that there are many books on +the subject at both a popular and a professional level of expertise, and I +had less to say about it than about some other areas. + +<P>The bibliography in Appendix A includes some pointers to information about +some of the missing topics. In any case, the purpose of this book isn't to +teach you everything there is to know about computers. It's to nurture in +you a sense of what computer science is like, or at least one +approach to computer science, in the hope that you'll be inspired to pursue +the study in the "regular" college-level texts. + +<P><H2>Computers and People</H2> + +<BLOCKQUOTE> +<P><A NAME="turkle">Steve</A> is a college +sophomore, an engineering student who had never thought +much about psychology. In the first month of an introductory +computer-science course he saw how seemingly intelligent and autonomous +systems could be programmed. This led him to the idea that there might be +something illusory in his own subjective sense of autonomy and +self-determination. + +<P> +Steve's classmate Paul had a very different reaction. He too came to ask +whether free will was illusory. The programming course was his first brush +with an idea that many other people encounter through philosophy, theology, +or psychoanalysis: the idea that the conscious ego might not be a free agent. +Having seen this possibility, he rejected it, with arguments about free will +and the irreducibility of people's conscious sense of themselves. In his +reaction to the computer, Paul made explicit a commitment to a concept of +his own nature to which he had never before felt the need to pay any +deliberate attention. For Paul, the programmed computer became the very +antithesis of what it is to be human. The programmed computer became part +of Paul's identity as not-computer. + +<P>Paul and Steve disagree. But their disagreement is really not about +computers. It is about determinism and free will. At different points in +history this same debate has played on different stages. Traditionally a +theological issue, in the first quarter of this century it was played out in +debate about psychoanalysis. In the last quarter of this century it looks +as though it is going to be played out in debate about machines. + +<P>--<EM>The Second Self: Computers and the Human Spirit,</EM> +Sherry Turkle, p. 23. +</BLOCKQUOTE> + +<P>The psychology of computer programming, the sociology of the +computer-intensive society, the economics of automation, the +philosophy of +mind, the ethics of computer use: these are the topics I find most +interesting and most important in thinking about computers. That's why I'm a +teacher instead of a computer programmer in industry. + +<P>In the original plan for this book there was to have been a chapter called +"Computers and People" at the end of the book. I feel strongly that it's +irresponsible to train people in the skills of computer technocracy without +also encouraging their sensitivity to the human implications of their work. +I ended up not writing that chapter, for several reasons. First, it would +have to be very different in tone from the hands-on, experimental style of +the rest of the book. I was afraid that, tacked on at the end, it would +sound preachy, or worse, tokenistic and hypocritical. So instead there is +this shorter discussion in the preface, where an author is allowed to +sound preachy. + +<P>Second, I'm not sure that the relevant issues can be presented usefully to +apprentices in the form of abstract reading. There is a lot of literature +on this side of computing, some of which is listed in the bibliography. But +the books, like all theoretical psychology or philosophy, are hard reading for +people whose relevant practical experience is just beginning. Instead I +think the best way to teach about the human side of computing is through +sensitive adult attention to the actual experiences that take place in the +computer center. (In general I've tried to write these books in a way that +leaves open exactly who is reading them. I think this sort of approach to +computer science can be useful to a wide range of people, kids and adults, +in and out of formal educational settings. But I guess right now I am +talking primarily to the teachers of high school students and +undergraduates.) + +<P>At my high school computer center the kids liked to write video game +programs. For a while some of the authors of these games included in the +programs a list of which other kids were or weren't allowed to play the +games. This practice let the game authors feel powerful and important, but +of course it wasn't very helpful to the community spirit in the computer +center. I didn't want to forbid the practice, making the issue one of rules +and authority. Instead, in conversation with the students I tried to turn +their attention away from ideas of intellectual property and +entitlement--"It's my program and I have the right to decide who can use +it"--and toward a sense of their own need for a strong community. Every +time you write a program you're building on the work of last year's students +who developed some of the techniques you use, on the work of people outside +the school who designed the programming language, operating system, and so +forth, and on the generosity of the adults in your community who paid for the +equipment you use. In the end, I think the issue was settled not so much by +my eloquence as by the example set by some other students who became +important members of the community through their willingness to help others +by teaching, encouraging, and sharing their own work. The kids all learned +that it's possible to be respected, admired, and loved instead of respected +but resented. + +<P>At many schools, when teachers express concern about the social issues in +the computer center, the main focus of that concern is around the question +of software piracy. Kids show up at school with a pirated version of the +latest microcomputer game program, very proud of themselves for having it, +and the teachers try to get the kids not to be proud of their theft of +intangible property. But it seems to me that the other side of the issue, +the spirit that's held up to kids as good computer citizenship, is marked by +secrecy, distribution of programs in compiled form only, copy protection that +works against networking, paranoia, and plain greed. I don't like <EM> +either</EM> side of that dichotomy. + +<P> + +<P>By contrast, in the university computer centers built around +timesharing systems or networked +workstations I see much more of a spirit of sharing, +openness, community, programs provided with source code so that people can +build on other people's work, trust, and an ideal of service to the +community. That's another reason I chose to set up a Unix system in +Sudbury. The ethical issues that arise in such a setting revolve around +privacy of information. Kids find it a challenge to break into other +people's accounts just as they do in the real-world computer systems that +get into the newspapers, but at school the person who gets angry is another +student rather than some faceless administrator. And students also +experience the positive moral force of software sharing and collaboration. + +<P>I'm exaggerating the differences; I know that there is cooperation among +microcomputer users and greed in the large computer world. Also, recent +hardware developments are making the boundary less clear; home computers and +workstations are built using the same processor chips. But the software is +different and I think the style of human interaction is different as well. +Still, the technical details of the facility are less important than the +teacher's willingness to be a humane model and not just a fount of +expertise. One of the virtues of that quaint idea of apprenticeship was +that the apprentice was involved in the <EM>entire</EM> way of life of the +master; there was no artificial separation between professional concerns and +human concerns. What goes on among the people in a computer center is at +least as important as what goes on between person and machine. + +<P> + +<P><A HREF="../v3-toc2.html">(back to Table of Contents)</A> +<P>[no back] +chapter thread <A HREF="ack.html"><STRONG>NEXT</STRONG></A> + +<P> +<ADDRESS> +<A HREF="../index.html">Brian Harvey</A>, +<CODE>bh@cs.berkeley.edu</CODE> +</ADDRESS> +</BODY> +</HTML> |