Faceted Classification
Complex subjects from
simpler components
Outline
• Prequel: Arrangement of concepts within
hierarchies.
• Goals of faceted classification.
• Basic design of faceted classifications.
• Facet analysis of complex subjects (factoring).
• Determination of facet structure.
• Faceted browsing on the Web.
Arrangement within hierarchies
Two forms:
• Showing multiple principles of division that
relate children to their parent node (subfacets).
• Ordering via appropriate principles at each
array (Ranganathan’s canons and such).
Showing principles of division
(subfacets)
shoes
high heels
hiking boots
mary-janes
pumps
running shoes
sandals
slingbacks
stilettos
wedges
winter boots
shoes
(by season)
winter
spring
(by function)
hiking
running
(by style)
boots
pumps
sandals
(by feature)
slingbacks
mary-janes
(by heel type)
stilettos
wedges
(by heel height)
high heels
Ordering concepts at each level
An “array” is a group of siblings (descriptors at the
same level of hierarchy). These should be ordered, even
if you don’t need subfacets. Possible orders:
• General to specific.
• Chronological.
• Close to far away.
• Order of a process.
Example: music tempos
Allegro
Andante
Largo
Moderato
Presto
Vivace
Largo
Andante
Moderato
Allegro
Vivace
Presto
(alphabetical)
(slowest to fastest)
Motivations for faceted classification
• The sheer number of documents keeps growing.
• The subjects of the documents are both more specific and more
complex.
• Knowledge itself is rapidly expanding—new subjects are
constantly being created.
It’s not helpful to put huge numbers of documents in general
subject categories (British History, Nuclear Physics). And yet we
can’t possibly enumerate all the possible subjects that either
currently exist or may soon exist. What to do?
Goals of faceted classification
If we can create a classification scheme that lists
subject components, then we can build complex
subjects out of the components as necessary.
We facilitate the construction of complex
subjects by organizing the component concepts
that make up our classification into facets, or
potential aspects of the subject.
From compound to components
Example of complex subject:
The history of Japanese tea-drinking etiquette
Components (or isolates, or factors): History + Japan + Tea +
Drinking + Etiquette
Potential fundamental categories (facets) for the components:
Disciplines (history); Locations (Japan); Beverages (Tea);
Activities (Drinking); Values (Etiquette)
Building subjects from components
A traditional faceted classification for libraries includes both the
facet structure of components and syntax rules for combining the
components into complex subjects.
These rules are necessary to ensure that documents are filed
consistently on shelves. (In an online environment, these rules
become superfluous.)
To “mechanize” the subject-building process and simplify filing,
components are given a notation (such as “soil acidity – sag” that
clarifies the component’s position within a facet.
Structure of faceted classifications
While a facet may be a simple list, components within a facet are
typically arranged hierarchically (using a stricter or looser sense
of hierarchy as appropriate).
Organic farming classification
Crops
Fruits
(by origin)
Vines
Grapes
Bushes
Trees
Vegetables
Herbs
Processes
Materials
Planting
Natural soil amendments
Controlling pests
Fertilizing
Compost
Mulch
Natural pesticides
Designing faceted classifications
1. Decompose complex concepts (which you have
gathered via your research into the subject literature)
into component parts, via syntactic or semantic
factoring.
2. Group the simple components into fundamental
categories.
3. Organize the components in each facet (with
hierarchical relationships, subfacets that indicate
multiple principles of division, order within arrays,
and so on).
Understanding complex concepts
There are two kinds of compounds:
• A multi-word unit (which may be a simple
concept, such as stained glass, or a complex
concept, such as glass cutting).
• A multi-concept unit (which may be a single
word, such as sourdough).
Syntactic and semantic factoring
Syntactic factoring: A term with multiple words is
divided into smaller components.
Example: rye bread into rye + bread; Irish emigration
into emigration + Irish
Semantic factoring: A term is divided into multiple
elementary concepts.
Example: apartment into dwelling + rental + shared
building.
Semantic factoring
Most standards/authorities don’t recommend semantic factoring,
and there aren’t rules you can use to help with it.
But semantic factoring can sometimes help you discover missing
concepts in your subject language.
It might be extreme to describe Passover as “holiday + Jewish +
commemoration + Exodus,” but doing so might make us consider
both religion and commemoration of events as aspects common to
many holidays.
Parsing compounds
A compound term consists of a focus (the class of things
or events) and a difference, which modifies the class and
makes a subclass.
Examples:
• Car tires: Focus is tires, difference is cars.
• Opera singing: Focus is singing, difference is opera.
• Mushroom hunter: Focus is hunter, difference is
mushroom.
Action/patient factoring
If the term contains an action (focus) modified by the recipient of
the action (difference), factor.
But if the term refers to a material (focus) as modified by an
action (difference), don’t factor.
Example:
Hair dyeing: hair + dyeing
Bronze engraving: bronze + engraving
But don’t factor: dyed hair, engraved bronzes
Part/whole factoring
If the focus refers to a part or property, and the difference refers
to the whole or the possessor of the part or property, factor.
But if the focus is the whole, and the difference is the part or
property, don’t factor.
Examples:
Soil acidity: soil + acidity
Library shelves: libraries + shelves
Don’t factor: acid soils, spare tires.
Action/performer factoring
If the term contains an intransitive action (focus) modified by the
performer (difference), factor.
If the performer (focus) is modified by its performance of an
intransitive action (difference), don’t factor.
Examples:
Student meeting: students + meetings
Lemur migration: lemurs + migrations
But don’t factor: migratory birds
Determination of facet structure
Ranganathan started from the top down: describing fundamental
categories (PMEST) for all subjects and organizing components
into those universal facets.
The Classification Research Group (CRG), as described by
Vickery, advocates beginning from the bottom up: reviewing
components and assigning preliminary fundamental categories
based on the concept’s definition within the classification’s
domain, then looking for commonalities in these preliminary
choices. Facets are specific to each classification.
Principles for creating facets
Spiteri, 1998, synthesized the following facet design
principles from Ranganathan and the CRG:
• Differentiation.
• Relevance.
• Ascertainability.
• Permanence.
• Homeogeneity.
• Mutual exclusivity.
Differentiation principle
When creating facets that split a group of entities,
choose a principle of division that cleanly splits the
group into component parts.
For example, dividing people by gender creates two
generally unambiguous categories. However, dividing
socks according to color can cause problems when
considering socks with multiple colors; color does not
provide the same level of differentiation for socks as
gender does for people.
More facet design principles
 Relevance: Choose facets based on the purpose of the
classification. A classification of gardening might divide terrain
by sun exposure, but a classification of cycling might divide
terrain by elevation.
 Ascertainability: When possible, choose facets that can be
reliably measured.
 Permanence: When possible, choose facets that will not
change over time.
Final facet design principles
 Homogeneity: Each facet (or subfacet) should represent a
single principle of division. For example, if we are classifying
socks, we should not see colors and patterns in the same array.
We would need to separate patterns and colors.
 Mutual Exclusivity: The contents of any two facets (or
subfacets) should not overlap (that is, they should be mutually
exclusive). If we are dividing shoes by heel height and by form,
we should not find any mixing of values for either facet (for
example, we should not see “high-heeled pumps” in the form
facet, but merely “pumps”).
Faceted browsing on the Web
Hearst’s Flamenco is an interface to support browsing of faceted
structures on the Web.
The Hearst article that you read describes how users preferred the
faceted browsing interface to a search engine when exploring the
collection.
(Note that the facets that Hearst used in the Flamenco system are
semi-automatically generated and not, perhaps, the best that one
might create...)
Your continuing mission
• Begin compiling a list of potential concepts for your
classification.
• Define an audience and purpose for your
classification, and use this, as well as your subject
knowledge, to more clearly define the scope of your
classification, its boundaries and its central and
peripheral areas.
• Begin defining each concept’s meaning in the context
of your classification.
Assignment progress checks
• No class on April 12; no office hours on April 11.
• Extra office hours will be scheduled for April 15, 16,
and 19. Sign up for a 15-minute slot (not required but
recommended).
• In these meetings, be prepared to tell me your subject,
audience, and purpose in a few sentences, and explain
how your classified structure represents your theory
of the subject.
• Bring assignment drafts to class on April 20 for peer
feedback sessions.