Author ID box for 2 column layout

This article examines the linguistic structure of folk-
sonomy tags collected over a thirty-day period from the 
daily tag logs of Del.icio.us, Furl, and Technorati. The 
tags were evaluated against the National Information 
Standards Organization (NISO) guidelines for the con-
struction of controlled vocabularies. The results indicate 
that the tags correspond closely to the NISO guidelines 
pertaining to types of concepts expressed, the predomi-
nance of single terms and nouns, and the use of recog-
nized spelling. Problem areas pertain to the inconsistent 
use of count nouns and the incidence of ambiguous tags 
in the form of homographs, abbreviations, and acro-
nyms. With the addition of guidelines to the construc-
tion of unambiguous tags and links to useful external 
reference sources, folksonomies could serve as a power-
ful, flexible tool for increasing the user-friendliness and 
interactivity of public library catalogs, and also may be 
useful for encouraging other activities, such as informal 
online communities of readers and user-driven readers’ 
advisory services.

O
ne of the most daunting challenges of information 
management in the digital world is the ability 
to keep, or refind, relevant information; book­

marking is one of the most popular methods for storing 
relevant Web information for reaccess and reuse (Bruce, 
Jones, and Dumais 2004). The rising popularity of social 
bookmark managers, such as Del.icio.us, addresses these 
concerns by allowing users to organize their bookmarks 
by assigning tags that reflect directly their own vocabu­
lary and needs. The collection of user­assigned tags is 
referred to commonly as a folksonomy. In recent years, 
significant developments have occurred in the creation 
of customizable user features in public library catalogs. 
These features offer clients the opportunity to customize 
their own library Web pages and to store items of interest 
to them, such as book lists. Client participation in these 
interfaces, however, is largely reactive; clients can select 
items from the catalog, but they have little ability to orga­
nize and categorize these items in a way that reflects their 
own needs and language.

Digital document repositories, such as library cata­
logs, normally index the subject of their contents via key­
words or subject headings. Traditionally, such indexing is 
performed either by an authority, such as a librarian or a 
professional indexer, or is derived from the authors of the 
documents; in contrast, collaborative tagging, or folkson­
omy, allows anyone to freely attach keywords or tags to 
content. Demspey (2003) and Ketchell (2000) recommend 

that clients be allowed to annotate resources of interest 
and to share these annotations with other clients with 
similar interests. Folksonomies can thus make significant 
contributions to public library catalogs by enabling cli­
ents to organize personal information spaces; namely, to 
create and organize their own personal information space 
in the catalog. Clients find items of interest (items in the 
library catalog, citations from external databases, external 
Web pages, and so on) and store, maintain, and organize 
them in the catalog using their own tags.

In order to more fully understand these applications, 
it is important to examine how folksonomies are struc­
tured and used, and the extent to which they reflect user 
needs not found in existing lists of subject headings. The 
purpose of this proposed research is thus to examine the 
structure and scope of folksonomies. How are the tags 
that constitute the folksonomies structured? To what 
extent does this structure reflect and differ from the 
norms used in the construction of controlled vocabular­
ies ,such as Library of Congress Subject Headings? What 
are the strengths and weaknesses of folksonomies (for 
example, reflect user need, ambiguous headings, redun­
dant headings, and so forth)?

This article will examine a selection of tags obtained 
from three folksonomy sites, Del.icio.us (referred to 
henceforth as Delicious), Furl, and Technorati, over a 
thirty­day period. The structure of these tags will be 
examined and evaluated against section 6 of the NISO 
guidelines for the construction of controlled vocabularies 
(NISO 2005), which looks specifically at the choice and 
form of terms.

■ Definitions of folksonomies
Folksonomies have been described as “user­created meta­
data . . . grassroots community classification of digital 
assets” (Mathes 2004). Wikipedia (2006) describes a 
folksonomy as “an Internet­based information retrieval 
methodology consisting of collaboratively generated, 
open­ended labels that categorize content such as Web 
pages, online photographs, and Web links.” The concept 
of collaboration is attributed commonly to folksonomies 
(Bateman, Brooks, and McCalla 2006; Cattuto, Loreto, 
and Pietronero 2006; Fichter 2006; Golder and Huberman 

The Structure and Form of 
Folksonomy Tags: The Road 
to the Public Library Catalog Louise F. Spiteri

Louise F. Spiteri (Louise.Spiteri@dal.ca) is Associate Professor 
at the School of Information Management, Dalhousie University, 
Halifax, Nova Scotia, Canada.

This research was funded by the OCLC/ALISE Library and 
Information Science Research Grant Program.

THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   13



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2006; Mathes 2004; Quintarelli 2005; Udell 2004). Thomas 
Vander Wal, who coined the term folksonomy, argues, 
however, that:

the definition of Folksonomy has become completely 
unglued from anything I recognize. . . . It is not col­
laborative . . . it is the result of personal free tagging 
of information and objects (anything with a URL) for 
one’s own retrieval. The tagging is done in a social 
environment (shared and open to others). The act of 
tagging is done by the person consuming the informa­
tion” (Vanderwal.net 2005).

It may be more accurate, therefore, to say that folk­
sonomies are created in an environment where, although 
people may not actively collaborate in their creation and 
assignation of tags, they may certainly access and use 
tags assigned by others. Folksonomies thus enable the 
use of shared tags. 

Folksonomies are used primarily in social bookmark­
ing sites, such as Delicious (http://del.icio.us/) and Furl 
(http://www.furl.net/), which allow users to add sites they 
like to their personal collections of links, to organize and 
categorize these sites by adding their own terms, or tags, 
and to share this collection with other people with the same 
interests. The tags are used to collocate bookmarks within a 
user’s collection and bookmarks across the entire system, so, 
for example, the page http://del.icio.us/tag/blogging will 
show all bookmarks that are tagged with blogging by any 
member of the Delicious site.

■ Benefits of folksonomies
Quintarelli (2005) and Fichter (2006) suggest that folk­
sonomies reflect the movement of people away from 
authoritative, hierarchical taxonomic schemes that reflect 
an external viewpoint and order that may not necessarily 
reflect users’ ways of thinking. “In a social distributed 
environment, sharing one’s own tags makes for innova­
tive ways to map meaning and let relationships naturally 
emerge” (Quintarelli 2005). Vander Wal (2006) adds that 
“the value in this external tagging is derived from people 
using their own vocabulary and adding explicit mean­
ing, which may come from inferred understanding of the 
information/object.” 

An attractive feature of folksonomies is their inclusive­
ness; they reflect the vocabulary of the users, regardless of 
viewpoint, background, bias, and so forth. Folksonomies 
may thus be perceived to be a democratic system where 
everyone has the opportunity to contribute and share tags 
(Kroski 2006). The development of folksonomies may 
reflect also the difficulty and expense of applying con­
trolled taxonomies to the Web: building, maintaining, and 
enforcing a sound, controlled vocabulary is often simply 

too expensive in terms of development time and of the 
steep learning curve needed by the user of the system 
to learn the classification scheme (Fichter 2006; Kroski 
2006; Quintarelli 2005; Shirky 2004). A further limitation 
of taxonomies is that they may become outdated easily. 
New concepts or products may emerge that are not yet 
included in the taxonomy; in comparison, folksonomies 
easily accommodate such new concepts (Fichter 2006; 
Mitchell 2005; Wu, Zubair, and Maly, 2006). Shirky (2004) 
points out that the advantage of folksonomies is not that 
they are better than controlled vocabularies, but that they 
are better than nothing.

Folksonomies follow desire lines, which are expres­
sions of the direct information needs of the user (Kroski 
2006; Mathes 2004; Merholz 2004). These desire lines also 
may reflect the needs of communities of interest: tag­
gers who use same set of tags have formed a group and 
can seek each other out using simple search techniques. 
“Tagging provides users an easy, yet powerful method to 
express themselves within a community” (Szekely and 
Torres 2005). 

■ Weaknesses of folksonomies
Folksonomies share the problems inherent to all uncon­
trolled vocabularies, such as ambiguity, polysemy, syn­
onymy, and basic level variation (Fichter 2006; Golder 
and Huberman 2006; Guy and Tomkin 2006; Mathes 
2004). The terms in a folksonomy may have inherent 
ambiguity as different users apply terms to documents 
in different ways. The polysemous tag port could refer 
to a sweet fortified wine, a porthole, a place for loading 
and unloading ships, the left­hand side of a ship or air­
craft, or a channel endpoint in a communications system. 
Folksonomies do not include guidelines for use or scope 
notes. Folksonomies provide for no synonym control; the 
terms mac, macintosh, and apple, for example, are all used 
to describe Apple Macintosh computers. Similarly, both 
singular and plural forms of terms appear (for example, 
flower and flowers), thus creating a number of redun­
dant headings. The problem with basic level variation 
is that related terms that describe an item vary along a 
continuum of specificity ranging from very general to 
very specific, so, for example, documents tagged perl 
and javascript may be too specific for some users, while 
a document tagged programming may be too general 
for others. Folksonomies provide no formal guidelines 
for the choice and form of tags, such as the use of com­
pound headings, punctuation, word order, and so forth; 
for example, should one use the tag vegan cooking or 
cooking, vegan? Guy and Tomkin (2006) provide some 
general suggestions for tag selection best practices, such 
as the use of plural rather than singular forms, the use 



ARTICLE TITLE  |  AUTHOR   15THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   15

of underscore to join terms in a multiterm concept (for 
example, open_source), following conventions estab­
lished by others, and adding synonyms. These sugges­
tions are rather too vague to be of much use, however; 
for example, under what circumstances should singular 
forms be used (such as noncount nouns), and how 
should synonyms be linked? 

■ Applications of folksonomies
Other than social bookmarking sites, folksonomies are 
used in commercial shopping sites, such as Amazon 
(http://www.amazon.com/), where clients tag items 
of interest; these tags can be accessed by people with 
similar interests. Platial (http://www.platial.com/
splash) is used to tag personal collections of maps. 
Examples of the use of folksonomies for intranets 
include IBM’s social bookmarking application Dogear, 
which allows people to bookmark pages within their 
Intranet (http://domino.watson.ibm.com/cambridge/
research.nsf/99751d8eb5a20c1f852568db004efc90/
1c181ee5fbcf59fb852570fc0052ad75?OpenDocument), 
and Scuttle (http://sourceforge.net/projects/scuttle/), 
an open­source bookmarking project that can be hosted 
on Web servers for free. PennTags (http://tags.library.
upenn.edu/) is a social bookmarking service offered by 
the University of Pennsylvania Library to its community 
members. Steve Museum is a project that is investigating 
the incorporation of folksonomies into museum catalogs 
(Trant and Wyman 2006). Another potential application 
of folksonomies is to public library catalogs, where users 
can organize and tag items of interest in user­specific 
folders; users could then decide whether or not to post 
the tags publicly (Spiteri 2006). 

■ Analyses of folksonomies
Analysis of the structure, or composition, of tags has thus 
far been limited; there has been more emphasis placed 
upon the co­occurrence of tags and their frequency of use. 
Cattuto, Loreto, and Pietronero (2006) applied a stochas­
tic model of user behavior to investigate the statistical 
properties of tag co­occurrence; their results suggest that 
users of collaborative tagging systems share universal 
behaviors. Michlmayr (2005) compared tags assigned to a 
set of Delicious bookmarks to the DMOZ (http://www.
dmoz.org/) taxonomy, which is designed by a commu­
nity of volunteers. The study concluded that there were 
few instances of overlap between the two sets of terms. 

Mathes (2004) provides an interesting analysis of the 
strengths and limitations of the structure of Delicious and 

Flickr, but does not provide an explanation of the meth­
odology used to derive his observations; it is not clear, for 
example, for how long he studied these two sites, how 
many tags he examined, what elements he was looking 
for, or what evaluative criteria he applied. 

Golder and Huberman (2006) conducted an analysis 
of the structure of collaborative tagging systems, look­
ing at user activity and kinds and frequencies of tags. 
Specifically, Golder and Huberman looked at what tags 
Delicious members assigned and how many bookmarks 
they assigned to each tag. This study identified a number 
of functions tags perform for bookmarks, including iden­
tifying the:

■ subject of the item;
■ format of the item (for example, blog);
■ ownership of the item; and
■ characteristics of the item (for example, funny).

While the Golder and Huberman study provides an 
important look at tag use, their study is limited in that 
they examined only one site for a period of four days; 
their results are an excellent first step in the analysis of 
tag use, but the narrow focus of their population and 
sample size means that their observations are not easily 
generalized. Furthermore, this study focuses more on 
how bookmarks are associated with tags (for example, 
how many bookmarks are assigned per tag and by 
whom) rather than at the structural composition of the 
tags themselves.

Guy and Tonkin (2006) collected a random sampling 
of tags from Delicious and Flickr to see whether “popular 
objections to folksonomic tagging are based on fact.” The 
authors do not explain, however, over what period the 
tags were acquired (for example, over a one­day period, 
over a month), nor to they provide any evaluative criteria. 
The tags were entered into Aspell, an open source spell 
checker, from which the authors concluded that 40 percent 
of Flickr and 28 percent of Delicious tags were either mis­
spelled, encoded in a manner not understood by Aspell, or 
consisted of compound words of two or more words. Tags 
did not follow convention in such areas as the use of case 
or singular versus plural forms. While this study certainly 
focuses upon the structure of the tags, the bases for the 
authors’ conclusions are problematic. It is not clear that 
the use of a spell checker is a sufficient measure of quality. 
Does the spell checker allow for cultural variations in spell­
ing (for example, labor or labour)? How well­recognized 
and comprehensive is the source vocabulary for this spell 
checker? Furthermore, if a tag does not exist in the spell 
checker, does this necessarily mean that the tag is incor­
rect? Tags may include several neologisms, such as podcast-
ing, that may not yet exist in conventional dictionaries but 
are well­recognized in a particular domain. The authors 
do not mention whether they took into account the cor­



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rect use of the singular form of such tags as noncountable 
nouns (for example, air) or tags that describe disciplines or 
emotions (for example, history and love). If a named entity 
(person or organization) was not recognized by Aspell, 
does this mean that the tag was classified as incorrect? 
Lastly, the authors seem to imply that compound words 
of two or more words are necessarily incorrect, which may 
not be the case (for example, open source software).

The pitfalls of folksonomies have been well­docu­
mented; what is missing is an in­depth analysis of the 
linguistic structure of tags against an established bench­
mark. While popular opinion suggests that folksonomies 
suffer from ambiguous and inconsistent structure, the 
actual extent of these problems is not yet clear; further­
more, analyses conducted so far have not established clear 
benchmarks of quality pertaining to good tag structure. 
Although there are no guidelines for the construction of 
tags, recognized guidelines do exist for the construction 
of terms that are used in taxonomies. Although these 
guidelines discuss the elucidation of inter­term relation­
ships (hierarchical, associative, and equivalent), which 
does not apply to the flat space of folksonomies, they 
contain sections pertaining to the choice and formation 
of concept terms that may, in fact, have relevance for the 
construction of tags.

■ Methodology
Selection of folksonomy sites

Tags were chosen from three popular folksonomy sites: 
Delicious, Furl, and Technorati (http://www.technorati.
com/). Delicious and Furl function as bookmarking 
sites, while Technorati enables people to search for and 
organize blogs. These sites were chosen because they 
provide daily logs of the most popular tags that have 
been assigned by their members on a given day. The 
daily tag logs from each of the sites were acquired over a 
thirty­day period (February 1–March 2, 2006). The daily 
tags for each site were entered into an Excel spreadsheet. 
A list of unique tags for each site was compiled after the 
thirty­day period; unique refers to the single instance of 
a tag. Some of the tags were used only once during the 
thirty­day period, while others, such as travel, occurred 
several times, so travel appears only once in the list of 
unique tags. Variations of the same tag—for example, 
car or cars, Cheney or Dick Cheney—were considered to 
constitute two unique tags. Only English­language tags 
were accumulated. 

The analysis of the tag structure in the three lists was 
conducted by applying the NISO guidelines for thesaurus 
construction, which are the most current set of recognized 
guidelines for the:

contents, display, construction . . . of controlled vocabu­
laries. This Standard focuses on controlled vocabularies 
that are used for the representation of content objects in 
knowledge organization systems including lists, syn­
onym rings, taxonomies, and thesauri (NISO 2005, 1). 

While folksonomies are not controlled vocabularies, 
they are lists of terms used to describe content, which 
means that the NISO guidelines could work well as a 
benchmark against which to examine how folksonomy tags 
are structured as well as the extent to which this structure 
reflects the widely accepted norm for controlled vocabu­
laries. Section 6 of the guidelines (term choice, scope, and 
form) was applied to the tags, specifically the following 
elements (see appendix A for the expanded list):

6.3 Term choice
6.4 Grammatical form of terms
6.5 Nouns
6.6  Selecting the preferred form

Only those elements in section 6 that were found to 
apply to the lists of unique tags are included in appendix 
A. For each site, the section 6 elements were applied to 
each unique tag; for example, it was noted whether a tag 
consists of one or more terms, whether the tag is a noun, 
adjective, or adverb, and so on. The frequency of occur­
rence of the section 6 elements was noted for each site and 
then compared across the three sites in order to determine 
the existence of any patterns in tag structure and the 
extent to which these patterns reflect current practice in 
the design of controlled vocabularies. 

Definition and disambiguation of tags

The meanings of the tags were determined based upon 
(1) the context of their use; and (2) their definition in three 
external sources, namely Merriam Webster online dic­
tionary (http://www.m­w.com/); Google (http://www.
google.com/); and Wikipedia (http://www.wikipedia.
org/). Merriam­Webster was used specifically to define all 
tags other than those that constitute unique entities (for 
example, named people, places, organizations, or products) 
and to determine the various meanings of tags that are 
homographs (for example, art or web). The actual concept 
represented by homographs was determined by examin­
ing the sites or blogs to which the tag was assigned. 

Merriam­Webster also was used to determine the 
grammatical form of a tag; for example, noun, verbal 
noun, adjective, or adverb. Determining verbal nouns 
proved to be complicated, especially given that NISO 
relies only on examples to illustrate such nouns. Some 
tags could serve as both verbal and simple nouns; for 
example, the tag clipping could describe the activity to clip 
or an item that has been clipped, such as a newspaper 



ARTICLE TITLE  |  AUTHOR   17THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   17

clipping. Similarly, does skiing refer to an activity, or the 
sport? If the dictionary defined a tag as an activity, the tag 
was classified as a verbal noun. In the case of tags that 
were defined as both verbal nouns and simple nouns, the 
context in which the tag was used determined the final 
classification. 

The dictionary also was used to determine the type 
of concept represented by a tag. The NISO guidelines do 
not define any of these seven types of concepts outlined 
in section 6.3.2; they provide only a short list of examples 
for each type. If the term represented by the tag was 
defined as an activity, property, material, event, discipline 
or field of study, or unit of measurement, it was classified 
as such unless the context of the tag suggested otherwise. 
If none of these six types was defined in the dictionary, 
the default value of thing was assigned to the tag. These 
definitions were then compared to the context in which 
the tag was used. In the case of the tag art, for example, an 
examination of the sites associated with this tag indicated 
that it refers to art objects, rather than the discipline, so it 
was classified as a thing. 

Merriam­Webster was used to determine whether a tag 
constitutes a recognized term in standard English (both 
United States and United Kingdom variants); for example, 
the tag blogs is a recognized term in the dictionary, while 
podcasting is not. NISO does not provide a clear definition 
of slang, neologism, or jargon, other than to say that they 
are nonstandard terms not generally found in dictionaries. 
Is the term podcasting, for example, an instance of slang, 
jargon, or neologism? At what point does jargon become 
a neologism? Because of the difficulty of distinguishing 
among these three categories, it was decided to use the 
broader category nonstandard terms to cover tags that (1) 
could not be found in the dictionary; or (2) are designated 
as vulgar or slang in the dictionary. 

Google and Wikipedia were used to define the mean­
ings of tags that constitute unique entities. Wikipedia also  
was used to distinguish the various meanings of tags that 
constitute abbreviations or acronyms via its disambigua­
tion pages; for example, the tag NFL is given eight pos­
sible meanings. In this case, the tag NFL is used to refer 
specifically to the National Football League, so the tag is a 
homograph, noun, and unique entry.

■ Tagging conventions and  guidelines of the folksonomy sites
Delicious

Delicious defines tags as:

one­word descriptors that you can assign to your 
bookmarks. . . . They’re a little bit like keywords but 
non­hierarchical. You can assign as many tags to a 

bookmark as you like and easily rename or delete them 
later. Tagging can be a lot easier and more flexible than 
fitting your information into preconceived categories or 
folders” (Del.icio.us 2006a). 

The Delicious help page for tags encourages people 
to “enter as many tags as you would like, each separated 
by a space” in the tag field. This paragraph explains 
briefly that two lists of tags may appear under the entry 
form used to enter a bookmark. The first list consists of 
popular tags assigned by other people to the bookmark 
in question, while the second consists of recommended 
tags, which contains a combination of tags that have been 
assigned by the client in question as well as other users 
(Del.icio.us 2006b). It is not clear how the two lists differ 
in that they both contain tags assigned by other people to 
the bookmark at hand.

The only tangible guideline provided about how tags 
should be structured is the sentence “your only limitation 
on tags is that they must not include spaces.” Delicious 
thus addresses only indirectly the fact that it does not 
allow multiterm tags; the examples provided suggest 
ways in which compound terms can be expressed; for 
example, San­francisco, SanFranciso, San.franciso (Del.
ico.us 2006b). Punctuation thus appears to be allowed in 
the construction of tags, which is confirmed by the sug­
gestion that asterisks may be used to rate bookmarks: “a 
tag of * might mean an OK link, *** is pretty good, and a 
bookmark tagged ***** is awesome” (Del.icio.us 2006b). It 
is thus possible that tags may not consist of recognizable 
terms, even though asterisks are neither searchable nor 
indicative of content. 

Furl

The Furl Web site uses the term topics rather than tags, 
but provides no guidelines or instructions for how to con­
struct these topics. Furl mentions only that when entering 
a bookmark, “a small window will pop up. It should have 
the title and URL of the page you are looking at. Enter any 
additional details (i.e., topic, rating, comments) and click 
Save” (Furl 2006). Furl provides all users with a list of 
default topics to which one can add at will. Furl provides 
no guidelines as to whether single or multiword topics 
may be used; it is only by trial and error that the user 
discovers that the latter are, in fact, allowed.

Technorati

In its tags help page, Technorati encourages users to “think 
of a tag as a simple category name. People can categorize 
their posts, photos, and links with any tag that makes 
sense” (Technorati 2006). A tag may be “anything, but it 
should be descriptive. Please only use tags that are rel­
evant to the post” (Technorati 2006). Technorati tags are  



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embedded into individual blogs via the link rel=”tag”; 
for example: <a href=”http://technorati.com/tag/
global+warming” rel=”tag”>global warming</a>. The tag 
will appear as simply global warming. No other guidelines 
are provided about how tags should be constructed.

As can be seen, the three folksonomy sites provide 
very few guidelines or conventions for how tags should 
be constructed. Users are not pointed to the common 
problems that exist in uncontrolled vocabulary, such as 
ambiguous headings, homographs, synonyms, spelling 
variations, and so forth, nor are suggestions made as to 
the preferred form of tags, such as nouns, plural forms, 
or the distinction between count nouns (for example, 
dogs) and mass nouns (for example, air). Given this lack 
of guidance, it is not unreasonable to assume that the tags 
acquired from these sites will vary considerably in form 
and structure.

■ Findings
Unless stated otherwise, the number of tags per folk­
sonomy site is 76 for Delicious, 208 for Furl, and 229 for 
Technorati. 

Homographs 

The NISO guidelines recommend that homographs—
terms with identical spellings but different meanings—
should be avoided as far as possible in the selection of 
terms. Homographs constitute 22 percent of Delicious 
tags, 12 percent of Furl tags, and 20 percent of Technorati 
tags. Unique entities constitute a significant proportion 
of the homographs in all three sites, with 71 percent in 
Delicious, 43 percent in Furl, and 55 percent in Technorati. 
The most frequently occurring homographs across the 
three sites consist predominantly of computer­related 
terms, such as Ajax and CSS. 

Single-word versus multiword terms

The NISO guidelines recommend that terms should 
represent a single concept expressed by a single or mul­
tiword term, as needed. Single­term tags constitute 93 
percent of Delicious tags, 76 percent of Furl tags, and 80 
percent of Technorati tags. The preponderance of single 
tags in Delicious may reflect the fact that it does not allow 
for the use of spaces between the different elements of the 
same tag; for example, open source. 

Types of concepts

NISO provides a list of seven types of concepts that may 
be represented by terms; while this list is not exhaustive, 

it represents the most frequently occurring types of con­
cept. Table 1 shows the percentage of tags that correspond 
to each of the seven types of concepts.

Tags that represent things are clearly predominant in 
the three sites, with activities and properties forming a 
distant second and third in importance. None of the tags 
represent events or measures, and only a fraction of the 
Technorati tags represent materials. The NISO guidelines 
provide no indication of the expected distribution of the 
types of concepts, so it is difficult to determine to what 
extent the three folksonomy sites are consistent with 
other lists of descriptors. None of the tags fell outside the 
scope of the seven types of concepts. 

Unique Entities

Unique entities may represent the names of people, places, 
organizations, products, and specific events (NISO 2005). 
Unique entities constitute 22 percent of Delicious tags, 
14 percent of Furl tags, and 49 percent of Technorati tags. 
There is no consistency in the percentage of unique enti­
ties: Technorati has nearly twice the percentage of tags 
than Delicious has, and nearly triple the percentage of tags 
than Furl has. Computer­related products constitute 100 
percent of the unique entities in Delicious, 63 percent in 
Furl, and 38 percent in Technorati. The remainder of the 
unique entities in Furl and Technorati represent places, 
people, and corporate bodies. The unique entities in 
Technorati are closely related to developments in current 
news events, an occurrence that is likely due to the site’s 
focus on blogs rather than Web sites. As will be discussed 
in a subsequent section, the unique entries constitute a 
significant proportion of the tags that represent ambiguous 
acronyms or abbreviated terms, such as Ajax or PSP. 

Table 1. Concepts represented by the tags

Delicious 
(%)

Furl  
(%)

Technorati 
(%)

Things 76 82 90.0

Materials 0 0 0.4

Activities 12 10 4.0

Events 0 0 0.0

Properties 8 6 4.0

Disciplines 4 3 1.0

Measures 0 0 0.0



ARTICLE TITLE  |  AUTHOR   19THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   19

Grammatical forms of terms

The NISO standards recommend the use of the following 
grammatical forms of terms:

■ Nouns and noun phrases 
■ verbal nouns
■ noun phrases 
■ premodified noun phrases 
■ postmodified noun phrases 

■ Adjectives
■ Adverbs

Table 2 shows the distribution of the grammatical 
forms of tags.

If all the types of nouns are combined, then 95 percent 
of Delicious tags, 94 percent of Furl tags, and 97 percent 
of Technorati tags constitute types of nouns. The gram­
matical structure of the tags in the three folksonomy sites 
thus reflects very closely the NISO recommendations that 
tags consist of mainly nouns, with the added proviso that 
adjectives and adverbs be kept to a minimum. None of 
the folksonomy sites used adverbs as tags, and the num­
ber of adjectives was very small, forming an average total 
of 5 percent of the tags. 

Nouns (plural and singular forms)

NISO divides nouns into two categories: Count nouns 
(how many?), and noncount, or mass nouns (how 

much?). NISO recommends that count nouns appear in 
the plural form and mass nouns in the singular form. 
NISO specifies other types of nouns that appear typi­
cally in the singular form:

■ Abstract concepts
■ beliefs; for example, Judaism, Taoism
■ activities; for example, digestion, distribution
■ emotions; for example, anger, envy, love, pity
■ properties; for example, conductivity, silence
■ disciplines; for example, chemistry, astronomy

■ Unique entities

Table 3 shows the distribution of the singular and plu­
ral forms of noun tags. The term singular nouns was used 
to collocate all the types of non­plural nouns. 

Table 3 represents the number of tags that constitute 
count nouns; this does not mean, however, that the tags 
appeared correctly in the plural form. Of the count nouns, 
36 percent of Delicious tags, 62 percent of Furl tags, and 
34 percent of Technorati tags appeared correctly in the 
plural form. It should be noted that although table 3 
indicates that properties constitute 8 percent of Delicious, 
6 percent of Furl, and 4 percent of Technorati tags, most 
of these tags are adjectives, and thus are not counted in 
the table. The NISO guidelines do not suggest the typical 
distribution of count versus singular nouns, but table 3 
indicates that at least among the three folksonomy sites, 
singular nouns form the bulk of the tags. 

Table 2. Grammatical form of tags

Delicious 
(%)

Furl  
(%)

Technorati 
(%)

Nouns 88 71 86

Verbal Nouns 5 6 4

Noun 
Phrases—
Premodified

1 15 4

Noun 
Phrases—
Postmodified

0 2 3

Adjectives 6 6 3

Adverbs 0 0 0

Table 3. Count and noncount noun tags

Delicious 
(%)

Furl  
(%)

Technorati 
(%)

Count nouns 18 35 23

Noncount 
nouns

77 59 74

Mass nouns 36 32 19

Activities 12 10 4

Properties 3 0 1

Disciplines 4 3 1

Unique 22 14 49

Total 95 94 97 



20   INFORMATION TECHNOLOGY AND LIBRARIES  |  SEpTEMBER 200720   INFORMATION TECHNOLOGY AND LIBRARIES  |  SEpTEMBER 2007

Spelling 

The NISO guidelines divide the spelling of terms into two 
sections: warrant and authority. With respect to warrant, 
NISO recommends that “the most widely accepted spell­
ing of words, based on warrant, should be adopted,” with 
cross­references made between variant spellings of terms. 
As far as authority is concerned, spelling should follow 
the practice of well­established dictionaries or glossaries. 

While spelling refers normally to whole words, I 
included in this analysis acronyms and abbreviations 
used to denote unique entities, such as countries or 
product names, as there are recognized spellings of such 
acronyms and abbreviations. Table 4 shows the tags from 
the three sites that do not conform to recognized spelling; 
the terms in italics show the accepted spelling.

The number of tags that do not conform to spelling 
warrant is clearly very few, constituting a total of 4 per­
cent of the Delicious tags, 3 percent of the Furl tags, and 2 
percent of the Technorati tags. Two of the nonrecognized 
spellings in Delicious are likely due to the difficulty of 
creating compound tags in this site, as was discussed 
earlier. The remainder of the tags conformed to recog­
nized spellings as found in the three reference sources 
consulted. The findings suggest that tags are spelled con­
sistently and in keeping with recognized warrant across 
the three folksonomy sites. Because of the international 
nature of the three folksonomy sites, no default English 
spelling was assumed. Table 5 shows those tags whose 
spellings reflect regional variations.

None of the three folksonomy sites featured lexical 
variants of any one tag. As the three sites are United 
States–based, the preponderance of American spelling 
is not surprising. What is surprising, however, is that 
Technorati features only the British variants in the total of 
tags examined in this study. It should be pointed out that 

the two lexical variants of these terms do appear in the 
three folksonomy sites; the two variants simply did not 
appear in the daily logs examined. No system to enable 
cross­referencing (for example, Humour USE or SEE 
Humor) exists in any of the three folksonomy sites, nor is 
cross­referencing discussed in the help logs of the sites.

Abbreviations, initialisms, and acronyms

NISO recommends that the full form of terms should be 
used. Abbreviations or acronyms should be used only 
when they are so well­established that the full form of 
the term is rarely used. Cross­references should be made 
between the full and abbreviated forms of the terms. 
Abbreviations and acronyms constitute 22 percent of 
Delicious tags, 16 percent of Furl tags, and 19 percent 
of Technorati tags. The majority of these abbreviations 
and acronyms pertain to unique entities, such as product 
names (for example, Flash, Mac, and NFL). In the case 
of Delicious and Furl, none of the abbreviated tags is 
referred to also by its full form. Four of the abbreviated 
Technorati tags have full­form equivalents:

■ Cheney/Dick Cheney
■ IE/Internet Explorer
■ Sheehan/Cindy Sheehan
■ UAE/United Arab Emirates

Abbreviations and acronyms play a significant role 
in the ambiguity of the tags from the three sites; they 
represent 71 percent of the abbreviated Delicious tags, 45 
percent of the abbreviated Furl tags, and 73 percent of the 
abbreviated Technorati tags. Furl and Technorati are very 
similar in the proportion of abbreviated tags used, but 
Delicious is significantly higher. The Delicious tags are 
focused more heavily upon computer­related products, 
which may explain why there are so many more abbrevi­
ated tags, as many of these products are often referred to 
by these shorter terms; for example, CSS, Flash, Apple, 
and so on.

Table 4. Tags that do not conform to spelling warrant

Delicious  
(N=76)

Furl  
(N=208)

Technorati  
(N=229)

Howto  
(How to)

Hollywood b-
day (Hollywood 
birthday)

Met-art pics 
(Metropolitan  
art pictures)

Opensource 
(Open 
source)

Med-books 
(Medical books)

Superbowl 
(Super Bowl)

Toread  
(To read)

Oralsex  
(Oral sex)

Web-20 
(Web2.0)

Table 5. Tags that reflect regional spelling variations

Delicious 
(N=76)

Furl  
(N=208)

Technorati 
(N=229)

Humor (U.S. 
spelling)

Humor (U.S. 
spelling)

Favourite 
(British 
spelling)

Jewelry (U.S. 
spelling)

Humour (British 
spelling)



ARTICLE TITLE  |  AUTHOR   21THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   21

Neologisms, slang, and jargon

The NISO guidelines explain that neologisms, slang, and 
jargon terms are generally not included in standard dic­
tionaries and should be used only when there is no other 
widely accepted alternative. Nonstandard tags do not 
constitute a particularly relevant proportion of the total 
number of tags per site; they account for 3 percent of the 
Delicious tags, 10 percent of the Furl tags, and 6 percent 
of the Technorati tags. The nonstandard tags refer almost 
exclusively to either computer­ or sex­related concepts, 
such as Podcast, Wiki, and Camsex. 

Nonalphabetic characters

This section of the NISO guidelines deals with the use of 
capital letters and nonalphabetic characters. Capitalization 
was not examined in the three folksonomy sites, as none 
of them are case sensitive; Delicious and Furl, for exam­
ple, post tags in lower case, regardless of whether the 
user has assigned upper or lower case, while Technorati 
shows capital letters only if they are assigned by the users 
themselves. The NISO guidelines state that nonalphabetic 
characters, such as hyphens, apostrophes (unless used for 
the possessive case), symbols, and punctuation marks, 
should not be used because they cause filing and search­
ing problems. Table 6 shows the occurrence of nonalpha­
betic characters in the three folksonomy sites.

A very small proportion of the tags in the three folk­
sonomy sites contains non­alphabetic characters, namely 

1 percent of the Delicious tags, and 3 percent of the Furl 
and Technorati tags. As was discussed previously, the 
Delicious help screens may encourage people to use 
nonalphabetic characters to construct compound tags; 
in spite of this, however, such characters are not, in fact, 
used very frequently. It should be noted that the terms 
above were all searched, with punctuation intact, in their 
respective sites; in all three cases, the search engines 
retrieved the tags and their associated blogs or Web sites, 
which suggests that nonalphabetic characters may not 
negatively impact searching.

■ Discussion and Recommendations
The tags examined from the three folksonomy sites cor­
respond closely to a number of the NISO guidelines 
pertaining to the structure of terms, namely in the types 
of concepts expressed by the tags, the predominance 
of single tags, the predominance of nouns, the use of 
recognized spelling, and the use of primarily alphabetic 
characters.

Potential problem areas in the structure of the tags 
pertain to the inconsistent use of the singular and plural 
form of count nouns, the difficulty with creating multi­
term tags in Delicious, and the incidence of ambiguous 
tags in the form of homographs and unqualified abbre­
viations or acronyms. As has been seen, a significant 
proportion of tags that represent count nouns appears 

incorrectly in the singular form. 
Because many search engines do 
not deploy default truncation, the 
use of the singular or plural form 
could affect retrieval; a search for 
the tag computer in Delicious, for 
example, retrieved 208,409 hits, 
while one for computers retrieved 
91,205 hits. Some of the results 
from the two searches overlapped, 
but only if both the singular and 
plural forms of the tags coexist. It 
would thus be useful for the help 
features of the folksonomy sites 
to explain the difference between 
count and noncount nouns and to 
discuss the impact of the form of 
the noun upon retrieval.

While all three sites conform 
to the NISO recommendation that 
single terms be used whenever 
possible, some concepts cannot be 
expressed in this fashion, and thus 
folksonomy sites should accom­
modate the use of multiterm tags. 

Table 6. Nonalphabetic characters

Delicious  
(N=76)

Furl  
(N=208)

Technorati 
(N=229)

Hyphens — Hollywood 
b-day; URL-
Project

Consumer-
Credit; Web-
2.0

Apostrophes — Mom’s medical 
(possessive)

Valentine’s Day 
(possessive)

Underscore Safari_export Blogger_life —

Full stop — Web 2.0 (part 
of product 
name)

Web-2.0 (part 
of product 
name)

Forward slash —  — /Africa

+ sign — JCR+ —



22   INFORMATION TECHNOLOGY AND LIBRARIES  |  SEpTEMBER 200722   INFORMATION TECHNOLOGY AND LIBRARIES  |  SEpTEMBER 2007

Furl and Technorati allow for their use, but make no 
mention of this feature in their help screens, which means 
that such tags may be constructed inconsistently—for 
example, by the insertion of punctuation—where a sim­
ple space between the tags will suffice. As has been seen, 
Delicious does not allow directly for the construction of 
multiterm tags, and in its instructions it actually promotes 
inconsistency in how various punctuation devices may be 
used to conflate two or three separate tags, once again at 
the detriment of retrieval, as is shown below:

Opensource: 103,476 hits 
Open_source: 91, 205 hits 
Open.source: 26,494 hits

Delicious should consider allowing for the insertion 
of spaces between the composite words of a compound 
tag; without this facility, users may be unaware of how 
to create compound tags. Alternatively, Delicious should 
recommend the use of only one punctuation symbol 
to conflate terms, such as the underscore. Furl and 
Technorati should explain clearly that compound tags 
may be formed by the simple convention of placing a 
space between the terms.

Ambiguous headings constitute the most problematic 
area in the construction of the tags; these headings take 
the form of homographs and abbreviations or acronyms. 
In the case of computer­related product names, it may be 
safe to assume that in the context of an online environ­
ment it is likely that the meaning of these product names 
is relatively self­evident. In the case of the tag Yahoo, for 
example, none of the sites or blogs associated with this 
tag pertained to “a member of a race of brutes in Swift’s 
Gulliver’s Travels who have the form and all the vices of 
humans, or a boorish, crass, or stupid person” (Merriam­
Webster 2007), but referred consistently to the Internet 
service provider and search engine. On the other hand, 
the tag Ajax was used to refer to Asynchronous JavaScript 
and XML technology as well as to a number of mainly 
European soccer teams. Given the international audience 
of these folksonomy sites, it may be unwise to assume 
that the meanings of these homographs are self­evident. 

Library of Congress Subject Headings often uses 
parenthetical qualifiers to clarify the meaning of terms—
for example, Python (Computer program language)—even 
though this goes against NISO recommendations. It 
is unlikely, however, that such use of parentheses will 
be effective in the folksonomy sites. A search for Opera 
(browser), for example, will likely imply an underlying 
AND Boolean operator, which detracts from the pur­
pose and value of the parenthetical qualifier; this was 
confirmed in a Furl search, where the terms Opera and 
Browser appeared either immediately adjacent to each 
other or within the same document. 

The application of the section of the NISO guidelines 
pertaining to abbreviations and acronyms is particularly 

difficult, as it is important to balance between using abbre­
viated forms of concepts that are so well­known that the 
full version is hardly used versus creating ambiguous tags. 
The fact that abbreviated forms appear so prominently in 
the daily logs of the three folksonomy sites suggests that the 
full forms of these tags are, in fact, very well­established. 
At face value, therefore, many of the abbreviated tags are 
ambiguous because they can refer to different concepts, but 
it is questionable whether such tags as CSS, Flash, Apple, 
and RSS, for example are, in fact, ambiguous to the users 
of the sites. The use of the full forms for these tags seems 
cumbersome, as these concepts are hardly ever referred to 
in their full form. It could possibly be argued, in fact, that in 
some cases, the full forms may not be familiar; I may know 
to what concept RSS refers, for example, without knowing 
the specific words represented by the letters R, S, S.

The possible ambiguity of abbreviated forms is com­
pounded by the fact that none of the three folkson­
omy sites allows for cross­references between equivalent 
terms, which is a standard feature of most controlled 
vocabularies, for example:

NFL/National Football League 
USE National Football League/Used For NFL

The help screens of the three sites do not address the 
notion of ambiguity in the construction of tags: They 
do not draw people’s attention to the inherent ambigu­
ity of abbreviated forms that may represent more than 
one concept. The sites also fail to address the fact that 
abbreviated forms (or any tag, for that matter) may be 
culturally based, so that while the meaning of NFL may 
be obvious to North American users, this may not be the 
case for people who live in other geographic areas. It may 
be useful for the folksonomy sites to add direct links to 
an online dictionary and to Wikipedia, and to encourage 
people to use these sites to determine whether their cho­
sen tags may have more than one application or meaning; 
I had not realized, for example, that RSS could represent 
twenty­three different concepts until I used Wikipedia 
and was led to a disambiguation page. Access to these 
external sources may help users decide which full version 
of the abbreviation to use in the case of ambiguity.

The examination of the structure of the tags pointed 
to some deficiencies in section 6 of the NISO guidelines, 
specifically its occasional lack of sufficient definition 
or explanation of some of its recommendations. The 
guidelines list seven types of concepts that are typically 
represented by controlled vocabulary terms, but rely only 
upon a few examples to define the meaning and scope of 
these concepts. The guidelines thus provide no consistent 
mechanism by which the creators of terms can assess 
consistently the types of concepts represented. How, 
for example, is a discipline to be determined? Does the 
term business represent a discipline if it is a subject area 
that is taught formally in a post­secondary institute, for 



ARTICLE TITLE  |  AUTHOR   23THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   23

example? Is it necessary for a discipline to be recognized 
as such among a majority of educational institutions? In 
its examples for events, NISO lists holidays and revolutions. 
It is unclear, however, what level of specificity applies to 
this concept; would Christmas, for example, be considered 
an event or a unique entity/proper noun (which is listed 
separately from types of concepts)? It is only later in the 
guidelines, under the examples provided for unique enti­
ties (for example, Fourth of July), that one may assume 
that a named event should be considered a unique entity. 
Verbal nouns also are difficult to determine based only 
upon the NISO examples, and once again no guidelines 
are provided to determine whether a noun represents an 
activity or a thing, or possibly both; for example, skiing 
or clipping. 

The lack of clear definitions in NISO also appeared in 
the section pertaining to slang, neologisms, and jargon, 
which are considered to be nonstandard terms that do not 
generally appear in dictionaries. As was discussed previ­
ously, it is not clear at what point a jargon term or a slang 
term becomes a neologism. All of the slang tags found in 
the three sites (for example, babe) appeared in Merriam­
Webster, which may serve to make this NISO section even 
more ambiguous. 

■ Conclusion
The most notable suggested weaknesses of folksonomies 
are their potential for ambiguity, polysemy, synonymy, 
and basic level variation as well as the lack of consistent 
guidelines for the choice and form of tags. The examina­
tion of the tags of the three folksonomy sites in light of the 
NISO guidelines suggests that ambiguity and polysemy 
(such as homographs) are indeed problems in the struc­
ture of the folksonomy tags, although the actual propor­
tion of homographs and ambiguous tags each constitutes 
fewer than one­quarter of the tags in each of the three 
folksonony sites. In other words, although ambiguity 
and polysemy are certainly problematic areas, most of the 
tags in each of the three sites are unambiguous in their 
meaning and thus conform to NISO recommendations. 

The help sites of the three folksonomy provide few 
tangible guidelines for (1) the construction of tags, which 
affects the construction of multiterm tags; and (2) the 
clear distinction between the singular and plural forms 
of count versus noncount nouns. As has been shown, 
the use of the singular or plural forms of terms, as well 
as the use of punctuation to form multiterm tags, affects 
search results. A large proportion of the tags in all three 
sites consists of single terms, which mitigates the impact 
on retrieval, but the inconsistent use of the singular and 
plural forms of nouns is indeed significant and thus may 
have marked effect upon retrieval. Synonymy and basic 

level variation were not examined in this study, but are 
certainly worthy of further exploration.

In other areas, the tags conform closely to the NISO 
guidelines for the choice and form of controlled vocabu­
laries. The tags represent mostly nouns, with very few 
unqualified adjectives or adverbs. The tags represent the 
types of concepts recommended by NISO and conform 
well to recognized standards of spelling. Most of the tags 
conform to standard usage; there are few instances of 
nonstandard usage, such as slang or jargon. In short, the 
structure of the tags in all three sites is well within the 
standards established and recognized for the construction 
of controlled vocabularies.

Should library catalogs decide to incorporate folkson­
omies, they should consider creating clearly written rec­
ommendations for the choice and form of tags that could 
include the following areas:

■ The difference between count and noncount nouns, 
as well as an explanation of how the use of the sin­
gular and plural forms affects retrieval.

■ One standard way in which to construct multiterm 
tags; for example, the insertion of a space between 
the component terms, or the use of an underscore 
between the terms.

■ A link to a recognized online dictionary and to 
Wikipedia to enable users to determine the meanings 
of terms, to disambiguate amongst homographs, and 
to determine if the full form would be preferable to 
the abbreviated form. An explanation of the impact 
of ambiguous tags and homographs upon retrieval 
would be useful.

■ An acceptable use policy that would cover areas 
of potential concern, such as the use of potentially 
offensive tags, overly graphic tags, and so forth. 
Although such terms were not the focus of this study, 
their presence was certainly evident in some cases, 
and would need to be considered in an environment 
that includes clients of all ages.

With the use of such expanded guidelines and links 
to useful external reference sources, folksonomies could 
serve as a very powerful and flexible tool for increasing 
the user­friendliness and interactivity of public library 
catalogs, and also may be useful for encouraging other 
activities, such as informal online communities of readers 
and user­driven readers’ advisory services.

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ARTICLE TITLE  |  AUTHOR   25THE STRUCTURE AND FORM OF FOLKSONOMY TAGS  |  SpITERI   25

Appendix A: List of NISO elements

6.3  Term Form
6.3.1   Single Word vs. Multiword Terms
6.3.2   Types of Concepts
   Terms for things and their physical parts
   Terms for materials
   Terms for activities or processes
   Terms for events or occurrences
   Terms for properties or states
   Terms for disciplines or subject fields
   Terms for units of measurement
6.3.3   Unique Entities
6.4  Grammatical Forms of Terms
6.4.1  Nouns and Noun Phrases
6.4.1.1    Verbal Nouns
6.4.1.2    Noun Phrases
6.4.1.2.1    Premodified Noun Phrases
6.4.1.2.2     Postmodified Noun Phrases
6.4.2  Adjectives
6.4.3  Adverbs
6.5 Nouns
6.5.1  Count Nouns
6.5.2  Mass Nouns
6.5.3  Other Types of Singular Nouns
6.5.3.1   Abstract Concepts
6.5.3.2    Unique Entities
6.6.2  Spelling
6.6.2.1    Spelling—Warrant
6.6.2.2    Spelling—Authorities
6.6.3  Abbreviations, Initialisms, and Acronyms
6.6.3.1    Preference for Abbreviation
6.6.3.2   Preference for Full Form
6.6.3.2.1     General Use
6.6.3.2.2     Ambiguity
6.6.4  Neologisms, Slang, and Jargon
6.7.1  Capitalization and Nonalphabetic Characters