W3C home > Mailing lists > Public > www-tag@w3.org > December 2005

Re: Initial Draft Finding on Principle of Least Power

From: Tim Berners-Lee <timbl@w3.org>
Date: Tue, 20 Dec 2005 13:22:32 -0500
Message-Id: <DE1DD872-BC2F-41A2-9662-0112ABE6786B@w3.org>
Cc: www-tag@w3.org
To: noah_mendelsohn@us.ibm.com

Noah,

Looks good, in general -- Thank you for doing it.

I had thought Roy had said a Principle was a reasonable epithet here  
- but I may remember wrongly.

The PLP bit was added to the Principles DesignIssues note at revision  
1.10, in January 2002.
I'm not sure whether it was taken from a previous location.

I'd like to change the wording of the bit about RDF to not talk about  
RDF in the HTML file
but compare and HTML file with an RDF file.  The business of mixing  
them is a distraction.

As regards SQL and truing completeness, I had assumed that it wasn't  
but then I seem to remember
being told it was.

Tim


Annotations for Principles.html
***************
1.10         (timbl    12-Jan-02): <!DOCTYPE html PUBLIC "-//W3C//DTD  
HTML 4.01 Transitional//EN"
1.10         (timbl    12-Jan-02):     "http://www.w3.org/TR/html4/ 
loose.dtd">
1.1          (timbl    09-Sep-99): <html>
1.1          (timbl    09-Sep-99): <head>
1.10         (timbl    12-Jan-02):   <meta http-equiv="Content-Type"  
content="text/html">
1.1          (timbl    09-Sep-99):   <title>-- Axioms of Web  
architecture</title>
1.9          (timbl    08-Jan-01):   <link rel="Stylesheet"  
href="di.css">
1.1          (timbl    09-Sep-99): </head>
1.1          (timbl    09-Sep-99):
1.10         (timbl    12-Jan-02): <body bgcolor="#ddffdd"  
text="#000000" lang="en">
1.1          (timbl    09-Sep-99): <address>
1.1          (timbl    09-Sep-99):   Tim Berners-Lee <br>
1.10         (timbl    12-Jan-02):   Date: 1998, last change: $Date:  
2001/01/08 19:23:50 $ <br>
1.10         (timbl    12-Jan-02):   Status: personal view only.  
Editing status: first draft.
1.1          (timbl    09-Sep-99): </address>
1.1          (timbl    09-Sep-99):
1.1          (timbl    09-Sep-99): <p><a href="./">Up to Design  
Issues</a></p>
1.1          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p></p>
1.2          (timbl    09-Sep-99): <hr>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <h1>Principles of Design</h1>
1.2          (timbl    09-Sep-99):
1.8          (timbl    09-Sep-99): <p>Again and again we fall back on  
the folklore of the principles of good
1.2          (timbl    09-Sep-99): design. Sometimes I need a URI for  
them so this is started as collection of
1.8          (timbl    09-Sep-99): them. I have written about some in  
many places.  Principles such as
1.10         (timbl    12-Jan-02): <b>simplicity</b> and  
<b>modularity</b> are the stuff of software
1.10         (timbl    12-Jan-02): engineering; <b>decentralization</ 
b> and <b>tolerance</b> are the life and
1.10         (timbl    12-Jan-02): breath of Internet.  Brian  
Carpenter has enumerated some principles of design
1.10         (timbl    12-Jan-02): of the Net [<a  
href="Architecture.html#carpenter">carpenter</a>]. The third
1.10         (timbl    12-Jan-02): pair of ideas I have found  
commonly useful for the Web. I mentioned them in a
1.10         (timbl    12-Jan-02): keynote at WWW7 and the note on <a  
href="Evolution.html">Evolvability</a>.</p>
1.5          (timbl    09-Sep-99):
1.10         (timbl    12-Jan-02): <p>This is largely "motherhood and  
apple pie" but it still needs a home.</p>
1.2          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <h2><a name="KISS">Simplicity</a></ 
h2>
1.2          (timbl    09-Sep-99):
1.7          (timbl    09-Sep-99): <blockquote>
1.7          (timbl    09-Sep-99):   <p>"Keep it simple, stupid!"</p>
1.7          (timbl    09-Sep-99): </blockquote>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p>Simplicity is easily to quote  
but often ignored in strange ways. Perhaps
1.2          (timbl    09-Sep-99): this is because it is the eye of  
the beholder.</p>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p>A language which uses fewer  
basic elements  to achieve the same power is
1.2          (timbl    09-Sep-99): simpler.</p>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p>Sometimes simplicity is  
confused with 'easy to understand". For example, a
1.2          (timbl    09-Sep-99): two-line solution which uses  
recursion is a pretty simple, even though some
1.2          (timbl    09-Sep-99): people might find it easier to  
work though a 10-line solution which avoids
1.2          (timbl    09-Sep-99): recursion.</p>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p>In XML, "Processing  
Instructions", those things which start with "&lt;?"
1.2          (timbl    09-Sep-99): are <strong>not</strong> simple.   
They look simple, just an extra sort of
1.2          (timbl    09-Sep-99): thing in the language, but the  
complicate what was a very clean design of
1.2          (timbl    09-Sep-99): elements and attributes, and a  
complication in the underlying syntax is has
1.2          (timbl    09-Sep-99): great effect. All specifications  
which refer to XML processing will have to
1.2          (timbl    09-Sep-99): figure out what to do about  
processing instructions as well as elements.</p>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <h2><a name="Modular">Modular  
Design</a></h2>
1.2          (timbl    09-Sep-99):
1.10         (timbl    12-Jan-02): <p>When you design a system, or a  
language, then if the features can be
1.10         (timbl    12-Jan-02): broken into relatively loosely  
bound groups of relatively closely bound
1.10         (timbl    12-Jan-02): features, then that division is a  
good thing to be made a part of the design.
1.10         (timbl    12-Jan-02): This is just good engineering.  It  
means that when you want to change the
1.10         (timbl    12-Jan-02): system, you can with luck in the  
future change only one part, which will only
1.10         (timbl    12-Jan-02): require you to understand (and  
test) that part. This will allow other people
1.10         (timbl    12-Jan-02): to independently change other  
parts at the same time. This is just classic
1.10         (timbl    12-Jan-02): good software design and books  
have been written about it.  The corollary,
1.10         (timbl    12-Jan-02): the TOII is less frequently met.</p>
1.3          (timbl    09-Sep-99):
1.3          (timbl    09-Sep-99): <p>Modular design hinges on the  
simplicity and abstract nature of the
1.3          (timbl    09-Sep-99): interface definition between the  
modules. A design in which the insides of
1.3          (timbl    09-Sep-99): each module need to know all about  
each other is not a modular design but an
1.3          (timbl    09-Sep-99): arbitrary partitioning of the  
bits.</p>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <h2 id="Tolerance">Tolerance</h2>
1.2          (timbl    09-Sep-99):
1.7          (timbl    09-Sep-99): <blockquote>
1.7          (timbl    09-Sep-99):   <p>"Be liberal in what you  
require but conservative in what you do"</p>
1.7          (timbl    09-Sep-99): </blockquote>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p>This is the expression of a  
principle which applies pretty well in life,
1.2          (timbl    09-Sep-99): (it is a typical UU tenet), and is  
commonly employed in design across the
1.2          (timbl    09-Sep-99): Internet.</p>
1.2          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <p>Write HTML 4.0-strict.  Accept  
HTML-4.0-Transitional (a superset of
1.4          (timbl    09-Sep-99): strict).</p>
1.3          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <p>This principle can be  
contentious.  When browsers are lax about what they
1.4          (timbl    09-Sep-99): expect, the system works better  
but also it encourages laxness on the part of
1.4          (timbl    09-Sep-99): web page writers.  The principle  
of tolerance does not blunt the need for a
1.4          (timbl    09-Sep-99): perfectly clear protocol  
specification which draws a precise distinction
1.4          (timbl    09-Sep-99): between a conformance and non- 
conformance. The principle of tolerance is no
1.5          (timbl    09-Sep-99): excuse for a product which  
contravenes a standard.</p>
1.4          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <p></p>
1.2          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <h2  
id="Decentrali">Decentralization</h2>
1.2          (timbl    09-Sep-99):
1.3          (timbl    09-Sep-99): <p>This is a principle of the  
design of distributed systems, including
1.10         (timbl    12-Jan-02): societies. It points out that any  
single common point which is involved in
1.10         (timbl    12-Jan-02): any operation trends to limit the  
way the system scales, and produce a single
1.3          (timbl    09-Sep-99): point of complete failure.</p>
1.3          (timbl    09-Sep-99):
1.3          (timbl    09-Sep-99): <p>Centralization in social  
systems can apply to concepts, too. For example,
1.3          (timbl    09-Sep-99): if we make a knowledge  
representation system which requires anyone who uses
1.5          (timbl    09-Sep-99): the concept of "automobile" to use  
the term
1.3          (timbl    09-Sep-99): "http://www.kr.org/stds/industry/ 
automobile" then we restrict the set of uses
1.3          (timbl    09-Sep-99): of the system to those for whom  
this particular formulation of what an
1.3          (timbl    09-Sep-99): automobile is works.  The Semantic  
Web must avoid such conceptual bottlenecks
1.10         (timbl    12-Jan-02): just as the Internet avoids such  
network bottlenecks.</p>
1.2          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <h2><a name="TOII">Test of  
Independent Invention</a></h2>
1.8          (timbl    09-Sep-99):
1.8          (timbl    09-Sep-99): <blockquote>
1.8          (timbl    09-Sep-99):   <p>If someone else had already  
invented your system, would theirs work with
1.8          (timbl    09-Sep-99):   yours?</p>
1.8          (timbl    09-Sep-99): </blockquote>
1.3          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <p>Does this system have to be the  
only one of its kind?  This simple thought
1.4          (timbl    09-Sep-99): test is described in more detail  
in "<a
1.4          (timbl    09-Sep-99):  
href="Evolution.html#TOII">Evolution</a>" in these Design Issues.  It is
1.4          (timbl    09-Sep-99): modularity inside-out: designing a  
system not to be modular in itself, but to
1.4          (timbl    09-Sep-99): be a part of an as-yet unspecified  
larger system. A critical property here is
1.10         (timbl    12-Jan-02): that the system tries to do one  
thing well, and leaves other things to other
1.4          (timbl    09-Sep-99): modules. It also has to avoid  
conceptual or other centralization, as no two
1.5          (timbl    09-Sep-99): modules can claim the need to be  
the unique center of a larger system.</p>
1.4          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <h2><a name="PLP">Principle of   
Least Power</a></h2>
1.4          (timbl    09-Sep-99):
1.10         (timbl    12-Jan-02): <p>In choosing computer languages,  
there are classes of program which range
1.10         (timbl    12-Jan-02): from the plainly descriptive (such  
as Dublin Core metadata, or the content of
1.4          (timbl    09-Sep-99): most databases, or HTML) though  
logical languages of limited power (such as
1.10         (timbl    12-Jan-02): access control lists, or  
<em>conneg</em> content negotiation) which include
1.10         (timbl    12-Jan-02): limited propositional logic,  
though declarative languages which verge on the
1.10         (timbl    12-Jan-02): Turing Complete (PDF) through  
those which are in fact Turing Complete though
1.10         (timbl    12-Jan-02): one is led not to use them that  
way (XSLT, SQL) to those which are
1.10         (timbl    12-Jan-02): unashamedly procedural (Java, C).</p>
1.10         (timbl    12-Jan-02):
1.10         (timbl    12-Jan-02): <p>The choice of language is a  
common design choice.  The low power end of
1.10         (timbl    12-Jan-02): the scale is typically simpler to  
design, implement and use, but the high
1.10         (timbl    12-Jan-02): power end of the scale has all the  
attraction of being an open-ended hook
1.10         (timbl    12-Jan-02): into which anything can be placed:  
a door to uses bounded only by the
1.10         (timbl    12-Jan-02): imagination of the programmer.</p>
1.10         (timbl    12-Jan-02):
1.10         (timbl    12-Jan-02): <p>Computer Science in the 1960s  
to 80s spent a lot of effort making
1.10         (timbl    12-Jan-02): languages which were as powerful  
as possible. Nowadays we have to appreciate
1.10         (timbl    12-Jan-02): the reasons for picking not the  
most powerful solution but the least
1.10         (timbl    12-Jan-02): powerful.  The reason for this is  
that the less powerful the language, the
1.10         (timbl    12-Jan-02): more you can do with the data  
stored in that language. If you write it in a
1.10         (timbl    12-Jan-02): simple declarative from, anyone  
can write a program to analyze it in many
1.10         (timbl    12-Jan-02): ways. The Semantic Web is an  
attempt, largely, to map large quantities of
1.10         (timbl    12-Jan-02): existing data onto a common  
language so that the data can be analyzed in ways
1.10         (timbl    12-Jan-02): never dreamed of by its creators.  
If, for example, a web page with weather
1.10         (timbl    12-Jan-02): data has RDF describing that data,  
a user can retrieve it as a table, perhaps
1.10         (timbl    12-Jan-02): average it, plot it, deduce things  
from it in combination with other
1.10         (timbl    12-Jan-02): information.  At the other end of  
the scale is the weather information
1.10         (timbl    12-Jan-02): portrayed by the cunning Java  
applet. While this might allow a very cool user
1.10         (timbl    12-Jan-02): interface, it cannot be analyzed  
at all. The  search engine finding the page
1.10         (timbl    12-Jan-02): will have no idea of what the data  
is or what it is about. This the only way
1.10         (timbl    12-Jan-02): to find out what a Java applet  
means is to set it running in front of a
1.10         (timbl    12-Jan-02): person.</p>
1.4          (timbl    09-Sep-99):
1.4          (timbl    09-Sep-99): <p>I hope that is a good enough  
explanation of this principle.  There are
1.4          (timbl    09-Sep-99): millions of examples of the  
choice.  I chose HTML not to be a programming
1.4          (timbl    09-Sep-99): language because I wanted  
different programs to do different things with it:
1.4          (timbl    09-Sep-99): present it differently, extract  
tables of contents, index it, and so on.</p>
1.1          (timbl    09-Sep-99):
1.1          (timbl    09-Sep-99): <p></p>
1.1          (timbl    09-Sep-99):
1.5          (timbl    09-Sep-99): <p></p>
1.5          (timbl    09-Sep-99): <hr>
1.5          (timbl    09-Sep-99):
1.5          (timbl    09-Sep-99): <h2><a  
name="References">References</a></h2>
1.5          (timbl    09-Sep-99):
1.5          (timbl    09-Sep-99): <p><a href="ftp://ftp.isi.edu/in- 
notes/rfc1958.txt" name="carpenter">B.
1.5          (timbl    09-Sep-99): Carpenter, Editor: "Architectural  
Principles of the Internet"</a> Internet
1.5          (timbl    09-Sep-99): Architecture Board, June 1996,  
RFC1958</p>
1.5          (timbl    09-Sep-99):
1.5          (timbl    09-Sep-99): <p></p>
1.1          (timbl    09-Sep-99):
1.2          (timbl    09-Sep-99): <p></p>
1.1          (timbl    09-Sep-99):
1.1          (timbl    09-Sep-99): <p></p>
1.1          (timbl    09-Sep-99): <hr>
1.1          (timbl    09-Sep-99):
1.1          (timbl    09-Sep-99): <p><a href="Overview.html">Up to  
Design Issues</a></p>
1.1          (timbl    09-Sep-99):
1.1          (timbl    09-Sep-99): <p><a href="../People/Berners- 
Lee">Tim BL</a></p>
1.1          (timbl    09-Sep-99): </body>
1.1          (timbl    09-Sep-99): </html>
Received on Tuesday, 20 December 2005 18:23:43 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 26 April 2012 12:47:37 GMT