ed or ignored. Tricks with mixed
s having “bridge” (or “doorway” or
“portal”) pages, designed as lus-
cious flies to webcrawlers, but
which quickly propel human
surfers to the real page;
s setting up a special portal page for
a specific search engine and sub-
mitting that page just to that
s entering into “mutual referent”
DESPERATELY agreements with other sites, so
your page appears to have many
links to it.
SEEKING If you’ve a particular search en-
gine in mind, check http://www.
Robert Filman • NASA Ames Research Center, Caelum Corp. searchenginewatch.com/webmasters/
• email@example.com features.html for a description of the
rating scheme and crawling behavior
of all the major search engines.
It is far more impressive when others to be listed first. Sullivan asserts the The site also presents “EKG” met-
discover your good qualities without three keys to being highly ranked are rics on search engines, graphing how
your help. deeply the major engines crawl over a
—Miss Manners (Judith Martin) s having the searched-for keywords site and how frequently they return to
in the page title, revalidate their links. Search Engine
SOME ARE s having the searched-for keywords Watch gives good marks to AltaVista
DISCOVERED, OTHERS appear early on the page, and and Northern Light (comprehensive
FOUND OUT. s having the searched-for keywords search and monthly refreshing).
In earlier columns, we’ve looked at appear frequently on the page. Inktomi was comprehensive, though
using search engines. Today, we start not as fresh; Excite was not as deep,
by grabbing the bull by the other Other factors include “link populari- though revisited frequently. Infoseek
horn, asking “How do I get search ty” (lots of other pages point to this had a middling comprehensiveness
engines to notice my site?” one), sites related to reviewed sites, and refresh rating. Lycos scores poorly
and information in metatags, though on depth, and Search Engine Watch
Search Engine Watch • use of these varies by engine. (Bribes didn’t find a pattern in its refresh rate
http://www. also work in some cases.) Sullivan (though that might mean, for exam-
searchenginewatch.com urges picking a two- or three-word ple, that Lycos refreshes the pages its
Danny Sullivan “strategic key phrase” and including it users find useful, rather than being
At Search Engine Watch, I found out in the title and early text. And, oh dumbly methodical).
more than I ever wanted to know yes, make sure the page has relevant Sullivan produces a free newsletter.
about search engines. Pages include content. I subscribed. For money, he promises
how to search, the histories of search Pitfalls include image maps (make even greater detail about search
engine companies, the economics of sure you have real html links to your engine behavior.
the search business, pointers to other subpages), frames (some search
pages discussing search engine issues, engines can’t handle them), and Ask Jeeves •
search engine trivia, performance dynamically generated pages (for http://www.ask.com
reports, and, most germane to our example, CGI). Sullivan advises sub- Of course, all these search engines
question, discussions on how to get mitting key pages to the major search require you to properly phrase a query
search engines to focus on a site. engines and periodically checking and sort the resulting wheat from chaff.
You can explicitly submit your that the pages remain referenced by How much better it would be if your
page to a search engine. However, the those engines. questions were directly answered. At
search engine may present your page Sites perceived guilty of spamming least that’s the sales pitch of Ask Jeeves:
as the 93rd best choice for its topic— (for example, by repeating a word too Type in a natural language question,
even though we all know that your frequently, putting text in the same and it takes you directly to the relevant
page contains all the greatest wisdom color as the background, or using an page—pages a human has picked out.
in the world on that topic and ought infinitesimal font) may be downgrad- The Spider paid a visit to try it out.
82 JULY • AUGUST 1999 http://computer.org/internet/ IEEE INTERNET COMPUTING
A R A C H N O I D T O U R I S T
Asking Jeeves “Why is the sky
blue?” produced the Blue Sky Exhibit The Spider’s rating system:
at National Center for Atmospheric
5 Flies = Scrumptious
Research. I guess that’s a direct hit,
but I never did see mention of lamb-
da to the fourth. Asking Jeeves “What 4 Flies = Tasty
is the meaning of life?” produced
3 Flies = Filling
Asked Questions about the Meaning
of Life, which assured me that 2 Flies = Edible
“Nobody who tried to ‘find the
meaning of life’ found it—what were 1 Fly = Yuck!
you originally looking for?” and
which stated its target audience was
“people experiencing emotional dis-
tress because they don’t know why
they’re getting up in the morning.” your site.) Good luck on finding your the LDAP server for that information.
Asking Jeeves “What are the 20 way back to something interesting. LDAP directories can be white pages,
largest islands in the world?” got me Jeeves seems to use the Parry algo- storing information about people, or
straight to a list of the world’s 25 rithm: Remember what people have yellow pages, storing information
largest islands, but asking “What are asked you. Have good answers for about resources. After all, supplying
the 20 largest islands in the United those questions. (Get a human to find Joe’s phone number isn’t radically dif-
States?” brought me to the same page. specific answers.) After a while, almost ferent from supplying the location of a
(The largest island in the United all the questions will repeat something virus protection program.
States, Hawaii, at 10,433 sq. km., you’ve already been asked. (Apparently The best introductory discussion
doesn’t begin to approach the size of more people care about sky color and of the uses and limitations of LDAP I
global number 25, Sri Lanka, at life meaning than the area of Long found was by Tim Howes, one of the
65,610 sq. km.) Jeeves also includes Island or HTTP-NG.) Of course, you authors of the original LDAP imple-
suggestions for similar questions. and I would never care about anything mentation at the University of
My U.S. islands question prompt- as unoriginal as something that had Michigan.
ed, “What are the islands of the already interested someone else. So we While LDAP directories can do any
world?” “Where can I find a concise don’t find Ask Jeeves all that useful. pairwise association, Howe points out
encyclopedia article on islands?” On the other hand, you can click a that you wouldn’t want to replace your
“Where is/are the United States of button on the Ask Jeeves page to see relational database system, file system,
America?” and “Where can I find a what everybody else is asking—a form or domain name server (DNS) with
financial calculator to help me deter- of amusement sure to provide that rea- LDAP—it’s not engineered to do any
mine which is better: 15- or 30-year son for getting out of bed. of those tasks well. Rather, LDAP’s
term mortgage?” I puzzled over that strength lies in ease of secure access.
last one, until I realized that Jeeves WHO ARE YOU LDAP arose as a simplified way to
was offering advice on how to finance Everyone keeps talking about LDAP, access X.500 services. ISO X.500 is a
the purchase of Sri Lanka. so I figured I’d have to find out what long-standing standard for a directory
Asking Jeeves “Where can I find it is. access system. Besides specifying a
the HTTP-NG proposed standard?” data model, X.500 has complex
reduced Jeeves to consulting its con- LDAP: Use as Directed • mechanisms for sharing data among
ventional search engine friends: http://www.data.com/ directory servers and forwarding
WebCrawler, Infoseek, Excite, and issue/990207/ldap.html requests that can’t be handled locally.
AltaVista. AltaVista returned nine rel- Tim Howes, Netscape LDAP started out as a “lightweight”
evant matches, WebCrawler and LDAP stands for “Lightweight access to X.500 servers, one that
Excite, three each, while Infoseek Directory Access Protocol,” with direc- could be run on a PC and didn’t
remained hung up on the “Where can tory being used in the same sense as in require the full implementation of the
I find” part. “phone directory.” That is, a company ISO network protocol. LDAP has
On the down side, Jeeves presents can keep, say, the names and phone evolved to its own standalone sys-
found pages within its own frame. numbers (or names and public keys) tem—LDAP servers are happy to run
This has the unfortunate side effect of of its employees in an LDAP directo- without an X.500 server in sight.
not disclosing the URL of the found ry, governed by a running server and LDAP borrows the X.500 data
page. (Another justification for the accessible over a network. Then any- model, which specifies a tree of
good design advice: include a link to one that needs, say, an employee domains (for example, organizations
your home page on all the pages of phone number, can remotely query and their suborganizations, like DNS)
IEEE INTERNET COMPUTING http://computer.org/internet/ JULY • AUGUST 1999 83
C O L U M N
with the leaves representing particular individuals. Names
are thus hierarchical. Leaves store a set of attribute value
sequences—that is, Joe’s phone numbers, address, fax num-
ber, favorite colors, and so forth. (See the diagram, “Getting
to the Root of LDAP,” at http://www.data.com/issue/
ADVERTISER / PRODUCT INDEX 990207/ldap_figure1.html.)
Advertiser / Products Page Number
Howe identifies eight basic components of LDAP.
Copper Mountain 15
s The information model (attributes and values and the
Cygnus Solutions 13 types of data). For example, the information model
might posit an attribute “Address” of type “String.”
Eprise Corp. 15
s The LDAP schema, the collections of attributes mak-
FlowPoint 15 ing up the records to be stored on a server.
s The naming model, describing the hierarchy of names
Hewlett Packard 13 (for example, gov.nasa.arc.rfilman).
IBM Corp. 13, 15 s The security model, including the ability to have both
client and server mutually prove their identities.
Informix 14 s The functional model, the behaviors of an LDAP sys-
Infoseek Cover 4 tem, including adding, modifying, and deleting records;
establishing connections; and searching.
Larscom 15 s The LDAP protocol, defining the mapping of the
Live Software 13 functionality to TCP/IP.
s The application program interface, providing a stan-
Lucent Technologies 15 dard set of calls for languages like C/C++, Java, and
Perl to access a directory.
s The data interchange format, a simple text format for
Netopia 15 representing data entries.
Network Appliance 13
Howe continues with a discussion of the limitations of the
Oracle 15 current LDAP standard and the directions for the next revi-
sion, version 3. Chief issues include improved replication
ParaSoft Corp. 1 and security. He closes with some examples of the benefits of
Perforce Software Cover 2 using LDAP, such as maintaining a centralized repository of
user passwords and phone information.
Red Hat Software 13 LDAP: the Next-Generation Directory •
Software Development Conf. ‘99 19, Cover 3 swol-10-ldap.html
Sun Microsystems 13,14 Dave Kosiur
Having gotten the LDAP overview from Howe, the Spider
Boldface denotes advertisers in this issue. crawled over to SunWorld for some implementation detail.
In this article, Dave Kosiur discusses some of the problems
Advertising Sales Offices of directory systems and goes into some detail about X.500
data structures, LDAP replication strategies, and the differ-
Sandy Aijala ences between the protocols. He notes that X.500 is not a
10662 Los Vaqueros Circle, Los Alamitos, CA 90720- tabula rasa. Rather, it comes with 17 predefined classes and
1314; Phone: (714) 821-8380; Fax: (714) 821-4010; 40 basic attribute types particularly oriented towards “phone
firstname.lastname@example.org book” applications. Kosiur also gives examples of LDAP
searches, including URLs that can be used to represent
Kim Newman,Gene Selven LDAP requests. Unfortunately, the article skips between
7291 Coronado Drive, Suite 8, San Jose, CA 95129; factoids without presenting a unified thesis.
Phone: (408) 996-7401; Fax: (408) 996-7871;
knewman@computer. org LDAP World •
For production information, conference, and classified advertising, Innosoft
contact Marian Anderson, IEEE Internet Computing, 10662 Los Want to find an LDAP product, a pointer to the LDAP
Vaqueros Circle, Los Alamitos, CA 90720-1314; Phone:(714) 821- FAQ, or track the changes in the LDAP standard? LDAP
8380; Fax:(714) 821-4010; email@example.com. World is devoted to keeping you up-to-date. A good
source of news and pointers.
84 JULY • AUGUST 1999 http://computer.org/internet/ IEEE INTERNET COMPUTING