(This is originally a chapter from the book Efficient information searching on the web.)
About directory services
The directory could be called the human search service as it’s the only one of the three search service types that is created and maintained by humans.
Three types of directories can be distinguished:
- General directories
- Subject directories
- Link collections
Principally it’s the size and direction that set them apart. The general directories are large, attempting to cover all subjects. The major general directories on the Net contain about 5 million links. The subject directories are, as the name suggests, concentrated on different subjects. The subject directories often have an academic focus, and their size can vary a lot. The link collections can be constituted by small collections of links that private persons have put together. But link collections are also often produced by different institutions or interest groups.
The character of directory services
Common for the directories is that they are organized and selective.
Organized because people have collected and structured the links, in contrast to the search engines which do everything automatically. Sometimes the links are also commented and labelled with subject words. Major directories have a hierarchical structure in which each subject has a given place. At times the subject hierarchy follows one of the library systems, e.g. the Swedish SAB system by which many libraries are arranged. Really high-class directories also have a standardized vocabulary, i.e. in the description of the links specific expressions and phrases are used to make them easier to find.
Selective because the links are chosen among many other links. Professional directory services publish their selection criteria so that everyone may know about them. You find more about the contents below.
To create and maintain a directory is demanding work. The maintenance work is often underrated which is why it’s neglected which, in turn, leads to the directory becoming obsolete. To minimize the maintenance work links which meet the criteria listed below are often chosen:
- Possess quality
- Created by authoritative originators
- Stable (not likely to move or change contents)
The link to the Swedish Government (www.regeringen.se) is very stable. The URL (the Web address) will probably be the same as long as the Web looks like it does today. For that reason directory editors often choose links to top-level pages (such as www.omis.se) and not links to pages far down in the structure, (for example www.omis.se/uppladdat/kurser/lub/lub-lankar.html). It’s much likelier that the later one will be changed or disappears, while the link to the top-level page normally is the last one to disappear.
When should you choose a directory?
- When you need to do a search for a broad subject or a broad idea.
- When you want to get a list with Web sites that are recommended or commented by experts.
- When you don’t want to look through a lot of documents that are not relevant.
Examples of general directories:
- Open Directory (http://dmoz.org)
- Yahoo! (http://dir.yahoo.com)
- Ipl2 (www.ipl.org) Librarians’ Internet Index (http://lii.org)
Universal subject structure
The large directories are general in regard to their contents and their structure builds on a “universal” subject structure. The subject structure in the general directories covers all conceivable subjects. Generally they have between 10 and 25 top categories and then follow large quantities of sub-categories.
The SAB system as an example of a universal subject structure
The SAB system is the most common classification system in Swedish libraries. The system was created in the beginning of the 20th century, just like many of the other library classification systems, and it reflects the time of its creation. One example of this is that the military system has been given a letter of its own, S, while economics and trade on Q covers everything from national economics to cookery books and cooking.
|A||Books and libraries|
|D||Philosophy and Psychology|
|E||Children and Education|
|H||Poetry and Fiction|
|L||Biography and Genealogy|
|M||Ethnography, Social Anthropology, Ethnology|
|N||Geography and Local History|
|O||Social Sciences and Law|
|P||Technology, Manufacturing and Transport|
|Q||Economics, Trade and Industry|
|R||Sports and Games|
|S||Military and Naval Systems|
Fig. The SAB system which is used in many Swedish libraries
All categories are divided into sub-categories. Category E, Children and Education, is divided into four blocks:
|Ex||Choice of Education|
Fig. Division of Children and Education (E) in the SAB system.
A letter or letter combination is called a signum. In the SAB system, one or several subject words are linked to each signum.
On the Web site of the National Library of Sweden you can do searches using different subject words and thus obtain the SAB codes. Or you can do a search using the SAB codes and get the subject words (www.kb.se/bibliotek/amnesord/sok-index/).
The Librarians’ Internet Index (LII), http://lii.org, has a different subject structure (see below).
Fig. The universal subject structure in LII.
The entries in the LII are ambitiously set up with descriptive texts and information about when the entry was created, by whom and when it was last modified. Each entry also has subject words according to the Library of Congress Subject Headings (LCSH), a US system run by the Library of Congress in Washington. To get more information about the entry you click on the magnifying glass after the heading.
Fig. Entries in lii.org on ”vikings” in the category of History
The placing of a subject in the hierarchy of subjects is not a given, but differs between the various directory services, see the example below.
The example of opera in different directories
|Yahoo! directory||Entertainment > Music > Genres > Classical > Opera|
|Open directory||Arts > Music > Styles > O > Opera|
|Internet Public Library||Arts & Humanities > Fine Arts > Performing Arts > Music > Opera|
The construction of directories
Directory services are created and maintained in different ways. You find one division between open and closed directories. The open directories are constructed by voluntaries, while the closed ones are run by a smaller group of salaried editors. The Open Directory (http://dmoz.org) is an open directory to which anyone can sign up for participation.
Examples of closed directories are commercial directories such as Yahoo! (http://dir.yahoo.com) and About (www.about.com), but also publicly funded directory services such as the Librarians’ Internet Index (http://lii.org).
Subject directories are directories that limit themselves to a subject area or to a type of resources, e.g. academic resources. Subject directories often focus on one academic area.
An example of a subject directory is Infomine (http://infomine.ucr.edu) from the US which contains large quantities of academic resources in different subjects.
Subject directories can have many names and come in many shapes. They can be called subject-based Internet gateways, subject gateways, subject portals or vortals (from vertical portal). And under the denomination “links” many things may be concealed.
The subject directories can be hard to find, particularly as they often constitute a minor part of the Web site of an interest group or a special library, perhaps hidden under the term “links”. If you only find them, navigation tools on the Web are among the most important instruments an information seeker can have.
Link collections are often quite small and often have just one editor. The contents are entirely dependent upon the editor’s subject interest and the will to keep the collection updated. Link collections seldom have any explicit quality requirements. But for information seekers link collections may be valuable, if you find a collection dealing with your subject.
Fig. Children’s Rights links from the Raoul Wallenberg Institute of Human Rights and Humanitarian Law library (http://www.rwi.lu.se/library/childrens.shtml)
Many directories are hard to classify. Some usable directories follow here below:
- Intute (www.intute.ac.uk)
- BUBL Link (http://bubl.ac.uk) (classifies according to Dewey)
Searching in the subject structure
The subject structure is often easy to find and there are often references between sub-categories further down in the structure (often designated with @). Some directories are structured according to a library system, e.g. the Swedish SAB system or the US Dewey system.
Searching with search words
The directories often offer search possibilities, generally through a search box. When it comes to searching in directories you have to consider that you only search within the directory, on the links and the comments. You don’t search on the contents of the linked pages, like you do in a search engine. Therefore you have to pick your search words with care and only do searches using one or two words.
What to consider regarding directories
How many entries or links does the directory contain?
Does the directory have a published policy about quality- and selection criteria?
What about the subject of the directory? The many resources on computers and programming may be seen as reflecting a bias on the Web.
Is the directory updated? The updating is often done slowly as it requires a manual control of each link.
Is payment required for inclusion of links in the directory? There are directories that make a living by demanding payment for inclusion of links in the directory. And then we’re not far from pure advertising services like the Yellow Pages.
Many commercial directories bring in supplementary links from a partner (a search engine). Consider the differences regarding search possibilities between a directory and a search engine (in practice the search takes place in a partner search engine).
Social bookmark services
New forms of directory service are the social bookmark services, also called social bookmark managers. A social bookmark manager is a Web site where you can save links and search among the bookmarks that other users have saved. The saved bookmarks are always accessible on the Web (unless you choose to make them private). The bookmark services generally allow you to provide the bookmarks with subject words, normally called tagging. The tags are unchecked subject words that each user picks individually, in contrast to the supervised subject words from subject word lists or thesauruses used in databases and certain directory services.
The largest social bookmark services are:
Comments are sometimes saved together with the tags. The comments can give a hint as to what other users think about the Web site to which the actual bookmark leads. Some of the bookmark services also use grading of the bookmarks which can also be helpful when you’re searching.
Popular tags are often presented in a tag cloud where more frequently used words are shown in bigger font and perhaps in a different colour. The font size depends entirely upon the usage of a tag. The result is not always correct as blog is distinguished from blogs and web2.0 from web 2.0 (with a space). But it’s a good tool to rapidly get a general view or to choose the used tag. All tags in the cloud link to all the bookmarks with the tag. In the figure below, design and blog are the most used tags.
Fig. The most popular tags as a tag cloud in Delicious.
In contrast to other search services, the social bookmark services build on popularity and up-to-dateness. Popular bookmarks are listed for each tag and popular links are bookmarked by still more people.
Fig. Popular bookmarks tagged with web2.0 on Delicious.
The figure above presents the most popular bookmarks for the tag web2.0 for the moment. The most recently bookmarked links for each tag are also often shown.
Sometimes tags closely related to the tag you have clicked on are shown. This may provide an easy way of getting closer to resources in the subject you’re looking for. The closely related tags to web2.0 in Delicious are shown below.
Fig. Related tags to web2.0 in Delicious.
The search possibilities vary as much of the usage builds on the tags. Generally you can click on a user name and get the bookmarks that this user has put up with a specific tag. For example, in Delicious active users are listed under closely related tags for each tag. Through studying that which the great taggers have bookmarked you can find both good and updated Web sites which you would probably not have found otherwise.
How social bookmark services are used for the storage of links is described in Chapter 14.