Title: --- Freely faceted classification for
Author: Claudio Gnoli
Company: Università di Pavia. Dipartimento di Matematica

Freely faceted classification for Web-based information retrieval

CLAUDIO GNOLI* and HONG MEI**

*University of Pavia. Department of Mathematics
via Ferrata 1, I-27100 Pavia, Italy, <gnoli@aib.it>

 **Tohoku University. Graduate school of Information science. Department of Human-social information sciences
Aramaki aza Aoba 09, Aoba-ku Sendai City Miyagi-pref. 980-8579, Japan, <mei@media.is.tohoku.ac.jp> 

This is a preprint of an article submitted for consideration in the 
NEW REVIEW OF HYPERMEDIA & MULTIMEDIA ©2006 Taylor and Francis;
NEW REVIEW OF HYPERMEDIA & MULTIMEDIA is available online at:
http://journalsonline.tandf.co.uk/

In free classification, each concept is expressed by a constant notation, and classmarks are formed by free combinations of them, allowing to retrieve records from a database through searching by any of the component concepts. A refinement of free classification is freely faceted classification, where notation can include facets, expressing the kind of relations holding between the concepts. The Integrative Level Classification project aims at testing free and freely faceted classification by applying them to small bibliographical samples in various domains. A sample called the Dandelion Bibliography of Facet Analysis is especially described here. Experience was gained by classifying with this system 300 specialized papers dealing with facet analysis itself recorded in a MySQL database, and building a Web interface exploiting freely faceted notation. The interface is written in PHP, and uses string functions to process the queries and to yield relevant results selected and ordered according to the principles of integrative levels.

Keywords: Free classification; Freely faceted classification; Integrative levels;  Multidisciplinarity; PHP language; Web search interfaces

Free classification and its roots

Bibliographic classifications, such as the Dewey Decimal Classification (DDC), the Universal Decimal Classification (UDC), or the Library of Congress Classification (LCC), are traditionally based on a top-down model: they divide the universe of knowledge into a few disciplines, such as philosophy, chemistry, or economics; then further divide each of them into more and more subclasses, which are expressed by an increasingly long notation. This is true also of faceted classifications such as the Bliss Bibliographic Classification 2nd edition (BC2).
This top-down model allows for some exploitment with digital information retrieval: e.g., a truncated classmark can be entered in a query, so to extract from the database all the records including that string as the beginning of the value in their notation field. Although this does yield meaningful sets of related documents, other documents are not retrieved, which deal with a same phenomenon under a different discipline – e.g., steel in technology instead that in chemistry. This happens because steel has a different notation in chemistry and in technology, due to the top-down disciplinary structure of the classification scheme. Indeed, Weinberg (1996) thinks that disciplinary schemes such as DDC are unsuitable to Web information retrieval, while an organization by specific subjects would be more effective. Williamson (1998) also questions the effectiveness of the traditional disciplinary approach, and wishes that research be done about the organization of multidisciplinary knowledge. Contemporary knowledge seems to become more and more interdisciplinary. For example, an astronomer charged with the inaugural speech for the last academic year at the University of Pavia described some recent major achievements of science by these words:
'NASA landed and controlled with ability and luck two rovers, which explored the surface of Mars [...]. It was a real miracle of engineering and robotics, beside astronautics, to get there. [...] In order to understand more about Mars, of course, we should send there a team of physicists, geologists, and biologists.' (Bignami 2005)
How could a disciplinary classification deal with such a subject as the complex of scientific and technical aspects of Mars exploration?
The work of the Classification Research Group (CRG) has pointed out that a different approach to classification is both possible (Foskett 1970) and more suitable in a digital environment (Austin 1974). That is a bottom-up approach, where first each phenomenon treated in documents gets a constant notation, and then classes are formed by combination of notation for component phenomena. In this way, steel has a fixed notation irrespective of being treated in chemistry or in technology, so that a query using the notation for steel can retrieve all documents dealing with it. A.C. Foskett (1973 pp. 106-107) called the two alternative approaches by fission and by fusion, using a metaphor sounding familiar in the time of the nuclear Cold War.
The earliest described version of bottom-up classification appears to be that experimented since 1926 by information consultant Edward G. Brisch, as reported by Kyle (1956). In the Brisch Building Classification, 'thermal properties of steel in making doors for refrigerators' is expressed as 13 35 538, where 13 = thermal properties, 35 = steel, 538 = refrigerators. In the system described by Kyle, these codes were actually punched on the edge of catalog cards, and information retrieval consisted of needling all the cards sharing holes in the requested positions. However, it can be easily seen that this is functionally equivalent to extracting from a database records having the requested strings in their notation field: in both cases, the set of relevant documents is selected by intersection of conditions (e.g. all records including both 35 and 538 must deal with the use of steel in refrigerators); conditions must be added or removed, until the set of results amounts to a satisfying manageable number between 1 and some tens (the typical futility point being about 30, according to Blair's (1980) tests). 
This kind of technique was also identified as free classification by Gardin (1965a), in a lucid paper where he opposes it to faceted classification. Indeed, in free classification every concept can be combined with any other and keep its notation, while in faceted classification notation for each subclass depends on its syntactical role within the context of the present discipline: steel can fill the facet of products in chemistry, but the facet of material in technology, or even the facet of objects in science of materials, etc.: this will produce in each case a different notation, not suitable for interdisciplinary information retrieval.
In its basic form, free classification is quite simple, as it just requires to analyse the subject of a document into its relevant semantic components, and to list their notations in order to get the classmark. At this stage, it is equivalent to assign the document a set of keywords taken from a thesaurus, with the only difference that concepts are expressed by codes instead of words. Such an approach is actually common in contemporary bibliographic databases, like MathSciNet for mathematics, Inspec for physics and information technology, and MedLine for medicine. As an example, the following are Inspec Classification codes taken from two Inspec records:
Title: An interactive visual interface for online product catalogs
Classification codes: 
C7250N		Search engines 
C7180 		Retailing and distribution computing 
C6130M 	Multimedia 
C7210N 		Information networks 
D2080 		Information services and database systems in IT 
D2140 		Marketing, retailing and distribution applications of IT 

Title: Overcoming information overload (taxonomy development)
Classification codes: 
D2080		Information services and database systems in IT 
D3045 		Records management systems for business automation 
D2010 		Business and professional IT applications 

Refining free classification

Although the system described is suitable to digital information retrieval from a technical point of view, it can turn out to be too rough in many cases where specialized indexing is required. Two features can then be useful to improve it. The most immediate one is to establish some standard rule for ordering the component concepts. Keywords are usually listed in alphabetical order, which is obviously empty of any semantic value, and free classification codes in the example above are listed in no apparent order. However, if codes are listed in a systematic order related to the schedules of the classification scheme, some helpful sequence in the compound classmarks will be produced, as in a browsable display the compound codes are filed under their first element. 
The CRG found that a consistent principle to order a general schedule of phenomena is that of integrative levels (Foskett 1961, Gnoli & Poli 2004), and that usually in classmarks the component concepts should be best listed in the reversed order of levels (Austin 1969). To keep our example, steel belongs to the low level of chemical substances, while refrigerators belong to the higher level of human artifacts, so that the compound notation should follow the inverted sequence refrigerators : steel.
A second possible improvement is to express the kind of relations between the component concepts. As Austin remarks, 
'keywords have achieved their most obvious success in the indexing of specialised collections of documents in fields such as engineering and metallurgy. These are disciplines which clearly fall within the "hard" sciences, which I would define as those fields of study in which (a) terminology is reasonably precise [...], and (b) in which the name of a thing also frequently suggests the grammatical role it is most likely to adopt in the majority of subjects being indexed. [...] However, we should not be able to deduce a subject with such confidence from a set of unrelated terms such as behaviour, modification, students, and teachers; each of these human beings is equally capable of assuming the active or the passive role' (Austin 1974). 

This problem calls for expressing relations between concepts by mean of some set of operators, playing a syntactical function similar to that of facets in classical faceted classifications; in this case, however, their syntactical function will be clearly separated from the semantic value of the component concepts (Gardin 1965a). Austin (1976) calls this more sophisticated kind of classification freely faceted classification, and we adopt this term. Freely faceted classification is still free, in the sense that notation for concepts does not depend on any disciplinary context and can be freely combined; at the same time, it uses facets to express relations between concepts where needed. (The phrase 'freely faceted classification' was used sometimes by Ranganathan (1967 section CY) with a slightly different meaning, that of a disciplinary classification where facets are not mandatorily expressed all in a rigid sequence; but this shade seems not to have spread in literature (Gatto pers. comm.).)
The technique of free facets has been implemented in two advanced subject indexing systems, Syntol (Gardin 1965b, Cros et al. 1968) and PRECIS (Austin 1984), both including rules to combine controlled terms by means of syntactical operators. Syntol and PRECIS work with verbal headings; however, the CRG research which led to PRECIS was originally conceived for a general classification system, and Austin (1974) saw classification as another future application of these principles.

The ILC project

'The quickest way to make clear a system of classification either to the layman or to the librarian is, after the briefest introduction, to demonstrate it by classifying and then retrieving items from a body of material.' (Kyle 1956)

After the 1970s, experimentation with these techniques has been neglected, as most attention was now focused on the rough power of computers and on keyword information retrieval. The same has happened in the first years of the Web, which have been dominated by search engines. However, the current rise of interest for knowledge organization and the Semantic Web shows that it is time to look back to advanced subject indexing, and to find ways of fruitfully integrating it with the digital tools, which in the meantime have become easily available to a much wider number of people.
A project was started in 2004 within the Italian chapter of the International Society for Knowledge Organization, called Integrative Level Classification (ILC) (ISKO Italia 2004). It takes as its starting point the research reports published by the CRG during the 1960s, concerning the possibility of a new general classification scheme based on phenomena rather than disciplines (Hong 2005). 
As CRG did not adopt a canonical sequence of disciplines anymore, some principle was needed to arrange phenomena into a standard sequence. This principle, as we mentioned before, was identified in the natural sequence of integrative levels of increasing complexity, each built on elements of the lower levels: subatomic particles, atoms, molecules, cells, organisms, societies, artifacts, institutions, etc. These are the main classes of a classification scheme of phenomena, as it was drafted by the CRG and reformulated for the ILC project:
A	 	information, structure
C		energy 
D 	time, space 
E		atoms 
F 	molecules 
G 	masses 
H 	rocks 
I 	celestial objects 
J 	weather 
K 	regions 
L 	cells 
M 	organisms 
N 	behaviour 
O 	reason 
P 	groups 
Q 	ecosystems 
R 	signals 
S 	agriculture, medicine 
T 	artifacts 
U 	economy 
V 	institutions 
W 	fiction 
X 	arts 
Y 	knowledge 
Z 	spirituality

Each main class can be divided into more specific classes, like in traditional classifications; again, subclasses are arranged when possible in order of integrative levels: to take an original example by D.J. Foskett, language is formed of a series of levels such as phonemes, morphemes, words, phrases, sentences, etc.:
R   signals, communication 
Rm   mimicry 
	Rp   displays 
Ru   language 
Ruf   phonemes 
Rum   morphemes 
Ruo   words 
Rus   phrases 
Rut   sentences 
Ruu   discourses

In a first stage, this notation can be used for free classification, by simply combining notations for concepts and listing them in reversed order of integrative levels: 
R Qr Mqvo	communication : forests : birds
Here the blank space expresses a generic relation between the component phenomena, which is called a phase relationship in Ranganathan's terms. However, as discussed above, in many cases such free classification can yield ambiguous classmarks. Therefore, a subsequent development in ILC was the introduction of facets, expressing typical relations of the lead concept with other concepts:
R2 [Q]		communication in environment... 
R4 [Mq]	communication by sender... 
R4vo2r 		communication by birds in forests

As it can be seen, ILC facets can imply a default broader class (written in square brackets in the schedules): communication (in the present sense) is always performed by some animal or human, hence Mq is implied by definition, and the resulting notation R4vo is shorter than the free combination of its component R Mqvo; it is also more precise, as the kind of relation is specified. 
The meaning of facets in a phenomenon-based classification, and the kinds of their definitions (involving what are called extra-defined foci and uniquely defined foci) are discussed in a separate paper (Gnoli 2006). Here we just mention that ILC facets are expressed by digits, which correpond to ten standard categories, analogous to those used by Ranganathan and by the CRG, and to some extent to Austin's operators:
0 	of size, measure 
1 	at time 
2 	in location 
3 	on patient 
4 	by agent 
5 	through process, tool 
6 	made of 
7 	related to, about 
8 	towards goal 
9 	in form

Of course, building a whole general classification scheme, which consistently keep an acceptable quality and the application of some logical principles is quite a titanic job, and is not among the present aims of the project. Classificationists achieving it, like Jack Mills and the Bliss Classification Association are now doing, deserve high consideration. However, to test the technique of freely faceted classification, it is enough to work with a draft of general scheme implementing the principles described by the CRG, and to develop detailed schedules only in some special domains, allowing to index limited samples of documents.
Another purpose of the project is to show the mechanisms of freely faceted classification by providing demos that can be tried by anyone. Therefore, Web interfaces are developed allowing to search and retrieve the sample records through queries that exploit the notational system.
The first stage of the tests was performed with a bibliography on a mountainous territory in Northern Italy, including its natural environment, its traditional culture, spoken dialects, etc., as part of a website devoted to it (Merli et al. 2005). The indexed documents, though being specialized in that they refer to a limited region, spread over many different knowledge domains. Therefore the rough general scheme was used, with the addition of a shortcut symbol @ standing for the locally preferred class, allowing to express the concept of the studied region with a shortened notation and to have it sorted first in systematic displays (Gnoli 2005). Symbols were combined mainly by listing them with blank spaces between, so to produce a free classification. The resulting classmarks are found to be quite effective and manageable. Only in some cases, such as 'The dialect of Portalbera and the wine terminology in Oltrepò pavese', subjects were complex enough to make the free combination of their elements ambiguous, just in the way reported by Austin. The bibliography currently amounts to about 450 records; its search and navigation interface is described in a separate paper (Gnoli & Merli 2005).
The second stage of the tests, currently under development, includes the use and exploitation of a faceted notation to index some collections of bibliographic references, each consisting of some hundreds records. At present, two faceted indexes have been only drafted, for references of scientific papers on animal communication, and for books on industrial innovation owned by an economics university library. As a third sample domain, facet analysis itself was chosen, and a faceted bibliography of it has been compiled by Hong, which is described in the next section. Incidentally, collaboration between a Chinese and a European classificationist can be taken itself as a test for the independence of the technique on any particular culture.

The Dandelion Bibliography of Facet Analysis

The sample for the second demo interface was given by titles dealing with facet analysis in both printed and digital documents. The first step was to select a representative sample of research papers on the subject, taken mainly from two sources. One of them was the Library and Information Science Abstracts (LISA) database at Toronto University, covering printed journals, many of which are actually owned in Toronto. LISA was searched in three days of the last week of June 2004, by the keywords 'facet' and 'faceted', and the results were around 100 items focusing on the years between 1960s to 2000. The Google Web search engine was also searched, by keywords like 'faceted classification', 'facet theory' etc., and the several thousands resulting Web pages were examined. Relevant references were dug out from LISA and Google results, and bibliography in them led to further references concerning faceted classification and its applications. A set of about 300 references was formed in this way.
This sample was christened the Dandelion Bibliography of Facet Analysis (DBFA), from a metaphor emerged during e-mail discussion between the authors: like the dandelion seeds fly in the air, information flies freely in the intellectual space, and freely faceted classification expresses its content; unlike appearance, it has a common background, like the seeds originally belong to one same flower. This unity of knowledge is expressed by the general scheme of the Integrative Level Classification, based on the ontological assumption of the unity and interconnection of reality.
On the other hand, the sample has a focus subject, which can be expressed by the context-depending symbol @, as it was seen in the previous example. In the DBFA, @ is equivalent to Yis 'knowledge organization systems, subject indexing systems', belonging to the following hierarchy in the ILC general scheme:
Y   knowledge
Yi   indexes
Yis   knowledge organization systems (KOSs)

In its debut, the focus class had five main subclasses, and only subclass @m were further developed:
@   knowledge organization systems (KOSs)
@e   keywords, vocabularies, glossaries
	@h   term indexes, thesauri
	@j   subject headings
	@m   systematic indexes, classifications
		@mc  Library of Congress Classification
			@md  Dewey Decimal Classification
			@me  Universal Decimal Classification
			@mf  Subject Classification
		@mg  Bliss Bibliographic Classification 1st edition
			@ml  Colon Classification
			@mr  Broad System of Ordering
		@ms  Bliss Bibliographic Classification 2nd edition
			@mt  Information Coding Classification
	@r   semantic networks, knowledge representation systems
	
Besides, facets were identified, both a-priori and on the basis of the literary warrant of the indexed documents. Facets of @, expressed by numerals, represent typical relations within the domain of KOSs: 
@1 [C^]	KOSs in period...
@2 [Vn^]  	KOSs made in area...
@3 [N^]  	KOSs for users...
@45 [N^]  	KOSs used by indexer...
@4 [N^:]  	KOSs developed by author...
		@4d  		KOSs developed by Dewey
		@4l   		KOSs developed by Ranganathan [etc.]
	@55 [Ru]   	KOSs in language...
	@5 [:]   	KOSs using models, approaches...
		@5b  		KOSs using enumeration
		@5f   		KOS using facet analysis
		@6 [:]   	KOSs with elements...
		@6c  		KOSs with concepts
		@6n   		KOSs with controlled terms, descriptors
		@6p   		KOSs with semantic relationships
			@6t   		KOSs with notation
	@79 [:]  	KOSs in kind of systems...
		@79g  		KOSs in general systems
			@79s  		KOSs in special systems
	@7 [Y7]  	KOSs of discipline, field
		@8 [:]   	KOSs for application...
		@8e  		KOSs for shelving
		@8i  		KOSs for information retrieval
		@8p  		KOSs for knowledge management
		@8r  		KOSs for information architecture
		@8t  		KOSs for teaching, education
	@9 [Yd]   	KOSs applied to documents...

In the schedule above, the codes in square brackets tell where the values of facets (the foci) should be taken from: [:] means that foci are uniquely defined in this very class, while other codes means that foci should be borrowed from other existing classes in the ILC scheme. For example, facet 9 borrows its foci from the subclasses of Yd 'documents': from
Ydc	images
Ydg 	maps
we get
@9c   	KOSs applied to images
@9g   	KOSs applied to maps

Like in disciplinary faceted schemes, facets can be combined with basic classes, starting from facets with higher numerals (inversion principle):
@m7u5f   faceted classification of economics
Facet 7 is for indexed fields of knowledge, and borrows its foci directly from the main classes (7u is from Y7u 'economics', which in turn comes from U 'economy'). While  doing the work, we realized that we also needed a facet for general vs. special schemes, and that it should have been a separate one from 7: indeed, we had papers about 'how social sciences are treated in general schemes' and others about 'special schemes for social sciences', which are different meanings. The concept of general vs. special schemes belongs to category 7 too, but as 7 was already used for disciplines, we introduced a separate facet with two-digit notation, 79, expressing both the similarity and the difference:
@m7u79g   general classification schemes dealing [also] with economics
@m7u79s   special classification schemes dealing with economics
Indeed, more than ten facets can be defined, if needed, by using two-digit notations (another example in the scheme above is 55).
Although it only covers a special domain, we cannot give here all the details of the scheme. Rather, we will show the possibilities of freely faceted classification in flexibility and depth by a complex example that we actually faced: a paper by Solomon, Bishop & Bresser entitled 'Organization moderators of gender differences in career development: a facet classification'. To begin with, from
	U   economy
		Ue   labour

we can get @m7ue5f 'faceted classification of labour', which seems a reasonable approximation of the subject on hand. However, it leaves out the factor of 'gender', which should be related to the concept of 'labour' (career development) rather than the lead concept of 'classification'. Therefore we consider 
	M^  	humans, people
		M^9   	people of gender...
			M^9f	women
			M^9m	men

Ue4 [M^]  	labour by workers...
	Ue4(9)   	labour by workers of gender...
		Ue4(9f)	labour by women

9f is in brackets because it is not directly a facet of Ue 'labour', but of its facet Ue4 'by workers': in other words, it is a subfacet. Subfacets are enclosed in round brackets to avoid ambiguous meanings and to produce a consistent sorting in systematic displays. Therefore, a more accurate (and complex) code for the document under examination is @m7ue(4(9))5f 'faceted classification of labor by gender'. We could go on and express 'faceted classification of women labour' as @m7ue(4(9f))5f.
Two final examples will illustrate the combination of free classification (phase relationships across different domains) with facets. A paper by Beghtol entitled 'Facets as interdisciplinary undiscovered public knowledge: S.R. Ranganathan in India and L. Guttman in Israel' can be classified as Pn @5f4l 'communities : faceted KOSs developed by Ranganathan', as it deals with a comparison between the domains of sociology (studying the phenomenon of communities) and of KOSs, the latter being specified with two facets. Similarly, Dahlberg's 'The basis of a new universal classification system seen from a philosophy of science point of view' can be classified as Yp7yr @m79g  'philosophy of science : general classifications'.
At the present stage, notation for complex subjects is only a first approximation, and can be further discussed and improved. Through this process of discussing real cases, we are getting a more and more proper structure for the test scheme. The whole bibliographic sample in its current status, including the developed special scheme (Dandelion Subject Indexing Classification, DSIC), can be seen and searched online at <http://www.iskoi.org/ilc/dsic/demo.php>.

Structure of the database

In order to make the bibliographies available through the Web, data were stored into a MySQL database, hosted in an Apache server at the Mathematics department of the University of Pavia, and the PHP script language was used to generate the interface between the database and the website of the ILC project. Indeed, the combined use of Linux operative system, Apache Web server, MySQL database and PHP interface (sometimes shortened as LAMP) is known as an effective way to manage such applications. 
The database consists of two tables, one (DBFA) for the documents and the other (DSIC) for the classification scheme. The table for documents has one field for the classmark, and other fields for bibliographic information such as authors, title, publication details, etc. The classmark field is set to binary, which implies that small letters are considered as different from capital letters when matched against queries. 
The DSIC table is where most information suitable for machine exploitation is recorded. Besides this special application, its structure can be considered as a more general model for structuring the kind of information useful for the schedules of a freely faceted classification. The table consists of seven fields, described in the following. The first three of them are for notation of the present class and of other classes semantically related to it. The four remaining fields are for the verbal caption of the class and other related terms which can be useful in information retrieval, like it happens in thesauri (the combination of a classification schedule with a thesaurus has been called a classaurus by Bhattacharyya). An example of a record is:
Notation: 		@55
Definition: 		Ru
Dependent: 		[null]
Caption: 		KOSs in language
Synonyms: 		idiom
Related: 		dialect
Morphological: 	languages, idioms, dialects

Notation
This field contains the notation of the class. In case the class is a facet, notation ends by a numeral.

Definition 
This field is used only in facets, to tell where their foci should be borrowed from. In the schedule-format scheme of the examples above, its value is reported in square brackets. As we saw, it can be the notation of another class (including another facet), or the symbol : to mean that foci are uniquely defined here; a further possibility is symbol * meaning that foci can be borrowed from any main class.

Dependent 
This field may contain notation of a class from a different integrative level, being a semantic factor implicit in the definition of the present class but not expressed in its notation. Its value can be reported after symbol « in the schedule-format scheme. A simple example from the Apennine bibliography is class Xgou 'alpinism, climbing', whose Dependent field has value Km, which is the notation for 'mountains'. Indeed, the concept of alpinism implies that of mountain; but if all semantic factors were expressed in notation, classmarks would become awkwardly long. Therefore, factors not expressed in notation, but expected to be useful in searching, are recorded in this field: a user searching for 'mountains' will receive, among other results, a hint that he can shift to class 'alpinism' to retrieve more documents not recorded under 'mountains'. This function was imaginated by Foskett (1961) as a consequence of an integrative level classification scheme: 'A new feature has to be consciously incorporated in the alphabetical index, namely, a system of references from certain combinations of terms to at least the level above [...] I surmise that only the upward references would be necessary'.

Caption 
It contains the preferred term used to express the meaning of the class in English. Preferably it should be quite short, as it will be used in combination with other terms in browsable displays. Alternative versions in other languages can obviously be stored in a parallel field, as is done with Italian in the Apennine bibliography.

Synonyms 
It contains other terms that are considered as synonyms or quasi-synonyms of the caption in the appropriate context.

Related
It contains more terms which, though not being stricly synonym of the caption, are usually related to its meaning. According to Bates (1998), to increase the recall of searches, thesauri for information retrieval should include a large number of such terms: in chosing them, possible associations in the mind of users (which tend to form clusters of even 20-40 terms, none prevailing on the others) should be cared for more than formal rules. 

Morphological
It contains morphological variants of all the terms in the fields Caption, Synonyms and Related, such as singular/plural, American spellings, etc. Unlike the other fields, the value of this one is never displayed, but only used to automatically direct searches using a morphological variant to the appropriate classes, without requiring users to learn the morphological rules of the controlled vocabulary used.

The Web interface

The Web interface is written in PHP language embedded into the HTML code of  common Web pages. PHP acts as an intermediary between the Web page and the MySQL database where bibliographical information is stored.
Users can either search directly by author, title, and subject, or browse classes and their facets. Author and title searches work as in any database. Subject search, on the other hand, directs users to a set of classes associated with the term they have typed. Classes containing the term in any of the fields Caption, Synonyms, Related, or Morphological are presented. They can belong to different parts of the schema: e.g., if the term 'period' is searched, classes can be retrieved from integrative level D 'processes' (period of a movement), from integrative level H 'rocks' (stratigraphic periods), and from integrative level V 'institutions' (historical periods of human institutions); from these the user will select the one of interest to her.
Alternatively, one can browse classes displayed in hierarchical menus according to their notation, like in a common decimal classification. In case a class is browsed whose notation is also present in the fields Dependent or Definition of another class, the latter will be included in the displayed results; browsing class Ru will yield these classes:
@55 [Ru]  	KOSs in language
Ru 		languages
Rui 		Indoeuropean languages
Xl « Ru 	literature

where Rui is retrieved because it begins by Ru (as it is a subclass of it); facet @55 is retrieved because it contains Ru in its field Definition (as it was seen above); and Xl is retrieved because it contains Ru in its field Dependent (as the existence of literature depends on language).
Either by subject search or by browsing, the user comes to selecting a class. By clicking on the notation of the selected class, a query is launched into the database, that retrieves from the DBFA table all the records having the requested notation in their Notation field. The basic MySQL query is of the form 
SELECT * FROM dbfa WHERE notation like '%".$no."%' 
ORDER BY notation

Variable $no contains the notation of the class selected by the user. The  % wildcards mean that it can be followed by any number of other characters: this allows to retrieve all the hierarchically subordinated classes (e.g. query @m 'classifications' also retrieves @me  'Universal Decimal Classification', @ml 'Colon Classification', etc.); it also allows to retrieve classmarks including these classes combined in a phase relation with others, like in Ou @m 'cognition : classification'. Results are sorted by notation, yielding a useful order by the very nature of classification schedules.
All this is just ordinary exploitation of a classification scheme (although unfortunately rarely implemented in Web interfaces). Exploitation of phase relations as in Ou @m is allowed by what we have called free classification, and is functionally equivalent to retrieving keywords. What is more new and tested in our system, however, is exploitation of the field Definition, which is typical of a freely faceted classification based on integrative levels. To this purpose, the query above must be expanded, in order to retrieve the facets wherever they occur: notation Rui 'Indoeuropean languages' must retrieve not only classmarks including Rui, but also those including @55i 'KOSs in Indoeuropean languages', which are formed from facet @55 [Ru].
This expansion is realized by processing the selected notation $no through PHP string functions. These functions are very useful in treating notation of classification schemes in sophisticated ways. To the present purpose, the requested string is cutted in all its possible fragments (Rui, Ru + i, R + ui), and each of the head parts is searched in the field Definition through the whole scheme. As Ru is found as the value of the field Definition of @55, the tail i is appended to @55, and the resulting string @55i is included in the extended set of notations to be searched.
Still, as @55i is the focus of a facet, it could occur in a non-consecutive sequence combined with other facets, such as @m7g55i 'general classification systems in Indoeuropean languages'. To take this cases into account, in any facet notation (i.e. in any notation including numerals) a wildcard is inserted before the numerals: @%55i .
The final query has the form
SELECT * FROM dbfa WHERE 
notation like '%".$no."%' OR
notation like '%".$no1."%' OR [etc.]
notation like '%".$no2."%' OR [etc.]
ORDER BY notation
where $no1, $no2 etc. are the notations of possible facets such as @%55i. In this way, results will include all the classmarks where either the basic notation, like Rui, or facets built from it, like @55i, occur in any combination with other classes.

Discussion

All this might look complicate. However, the whole processing of the query happens in fractions of seconds, and users need not to be aware of all the mechanism. Though they can guess it by inspecting classmarks, so getting an idea of the usefulness of classification, what they will see more emphasized in the interface will be the verbal captions and the descriptions of the associated documents. The test interfaces currently available in the project website do not have all these particulars yet fully integrated and explained, but this will be an easy development once the core mechanism is set up. It is our intention to develop them in the next months. The project website will always include the most evolved interfaces currently available.
We must emphasize that what we have described is a work in progress, not a finished system. Classification blueprint is a process that requires substantial interaction and feedback if it is to be successful. Obviously further changes must be expected, but what will be kept are the basic principles of freely faceted classification as they have been sketched here. At this stage, we hope that application in this special domain is enough at least to show the mechanism and the theoretical bases of the project. 
Testing with a special domain stimulates further development of the technique, by constructing a framework that mirrors the principles of freely faceted classification more accurately and makes them usable for practical exploitment. In other words, it provides challenges and suggestions to strengthen theoretical research.

References

Austin, D., Prospects for a new general classification. J. Librarianship, 1969, 1(3), pp. 149-169.
Austin, D., A conceptual approach to the organisation of machine-held files for subject retrieval. In Conceptual bases of the classification of knowledge: proc. of the Ottawa conference, October 1st-5th, 1971, edited by Jerzy A. Wojciechowski, pp. 371-398, 1974 (Verlag Dokumentation: Pullach bei München).
Austin, D., The CRG research into a freely faceted scheme. In Classification in the 1970s: a second look, edited by Arthur Maltby, pp. 158-194, 1976 (Bingley: London).
Austin, D., PRECIS: a manual of concept analysis and subject indexing, with assistance from Mary Dykstra, 2nd ed., 1984 (British Library: London).
Bates, M., Indexing and access for digital libraries and the Internet: human, database, and domain factors. J. Am. Soc. Info. Sci., 1998, 49, pp. 1185-1205. Available online at: www.gseis.ucla.edu/faculty/bates/articles/indexdlib.html (accessed 3 January 2006).
Bignami, G.F., Finché ci saranno stelle...: astronomia dallo spazio: prolusione all'anno accademico 2004-2005, 2005 (Università di Pavia: Pavia).
Blair, D.C., 1980, Searching biases in large interactive document retrieval systems. J. Am. Soc. Info. Sci., 17(3), pp. 271-277.
Cros, R.C., Gardin, J.C. and Lévy, F., L'automatisation des recherches documentaires: un modèle général: le SYNTOL, 2e ed., 1968 (Gauthier-Villars : Paris).
Foskett, A.C., The Universal Decimal Classification: the history, present status and future prospects of a large general classification scheme, 1973 (Bingley: London).
Foskett, D.J., Classification and integrative levels. In The Sayers memorial volume, edited by D.J. Foskett and B.I. Palmer, pp. 136-150, 1961 (Library Association: London). Republished in Theory of subject analysis: a sourcebook, edited by L.M. Chan, P.A. Richmond and E. Svenonius, pp. 210-220, 1985 (Libraries Unlimited, Littleton).
Foskett, D.J., Classification for a general index language: a review of recent research by the Classification Research Group, 1970 (Library Association: London).
Gardin, J.C., Free classifications and faceted classifications: their exploitation with computers. In Classification research: proc. of the international conference, Elsinore, 1964, edited by P. Atherton, pp. 161-176, 1965a (Munksgaard: Copenhagen).
Gardin, J.C., Syntol. In Systems for the intellectual organization of information, edited by S. Artandi, vol. 2., 1965b (Rutgers Univ. Press: New Brunswick).
Gnoli, C., Classificazione a livelli per una bibliografia web di cultura locale. In Classificare la documentazione locale: giornata di studio, San Giorgio di Nogaro, 17 December 2005. Available online at: www.iskoi.org/doc/locale3.htm (accessed 3 January 2006).
Gnoli, C., The meaning of facets in nondisciplinary classifications. In Knowldege Organisation for a global learning society: ninth ISKO international conference, Vienna, 4-7 July 2006. 
Gnoli, C. and Merli, G. Notazione e interfaccia di ricerca per una classificazione a livelli, AIDA informazioni, 2005, 23(1-2), pp. 57-72. English abstract available online at: www.aidainformazioni.it/2005/122005.html#articoli (accessed 3 January 2006).
Gnoli, C. and Poli, R. Levels of reality and levels of representation. Knowledge organization, 2004, 31(3), pp. 151-160.
Hong M., A phenomenon approach to faceted classification [in Japanese]. In 53th conference Japan Soc. Library and Info. Sci., Keio University, 22-23 October 2005. English abstract available online at: http://www.iskoi.org/ilc/phenomenon.htm (accessed 3 January 2006).
ISKO Italia, Integrative level classification: research project, 2004-. Available online at: www.iskoi.org/ilc (accessed 3 January 2006).
Kyle, B., E.G. Brisch: something new in classification. Special Libraries, 1956, 47(3), pp. 100-105.
Merli, G., Bisi, F. and Gnoli C., Books and papers. In Ferrari, P., Gnoli, C. and Paveto, F., Where the Apennine begins, 2004-. Available online at: www.iskoi.org/ilc/4p/index.en.php (accessed 3 January 2006).
Ranganathan, S.R., Prolegomena to library classification, with assistance of M.A. Gopinath, 1967 (SRELS, Bangalore).
Weinberg, B.H., Complexity in indexing systems: abandonment and failure: implications for organizing the Internet. In ASIS 1996 annual meeting, Baltimore, 19-24 October 1996. Available online at www.asis.org/annual-96/ElectronicProceedings/weinberg.html php (accessed 3 January 2006).
Williamson, N.J., An interdisciplinary world and discipline based classification. In  Structures and relations in knowledge organization: proc. 5th ISKO conference,  Lille, 25-29 August 1998, edited by  W. Mustafa El Hadi, J. Maniez and A.S. Pollitt, pp. 115-124, 1998 (Ergon: Würzburg).