Defining Presentation Information
This page discusses the notion of "presentation information" in the transfer and display of thesauri and classification schemes.
The purpose of this discussion is to establish clear criteria for the scope of SKOS - what it is, and is not, required to represent.
This discussion is closely related to the discussion of SkosDesign/GroupingConstructs.
There are two well-known types of display for thesauri: alphabetic display and systematic display.
Thesaurus Alphabetic Display
From [ISO 2788-1986] section 9.2 ("Alphabetic Display"):
In this form of thesaurus all indexing terms, whether preferred or non-preferred, are organized as a single alphabetical sequence. Non-preferred terms are usually accompanied only by references (for example USE) to their preferred equivalents. Where ancillary information is appended to preferred terms it should be listed in the following order:
1) SN scope notes or definitions.
2) UF references to non-preferred equivalent term(s).
3) TT references to top terms, if necessary.
4) BT references to broader terms.
5) NT references to narrower terms.
6) RT references to related terms.
TT OPTICAL EQUIPMENT
NT UNDERWATER CINE CAMERAS
Note, however, that there are no absolute rules for constructing an alphabetic display. For example, all of the references (SN, BT etc.) are optional.
Now consider the following RDF graph:
# conventional prefixes ex:A skos:prefLabel "OPTICAL EQUIPMENT"@en; skos:narrower ex:B. ex:B skos:prefLabel "CAMERAS"@en; skos:narrower ex:C. ex:C skos:prefLabel "UNDERWATER CAMERAS"@en; skos:narrower ex:D; skos:related ex:E. ex:D skos:prefLabel "UNDERWATER CINE CAMERAS"@en. ex:E skos:prefLabel "DIVING"@en.
Given this graph, it is possible to define an algorithm to generate a default thesaurus alphabetic display such as the example shown above, where all references (SN, BT etc.) are shown and in the order suggested by [ISO 2788-1986].
However, the algorithm would need to be supplied with additional information, such as font family, font size, rules for font weight and text decoration, horizontal indentation of references, vertical spacing between entries etc.
Also, as noted above, there are no absolute rules for constructing an alphabetic display, and all of the references (SN, BT etc.) are optional.
Therefore, the following statements are proposed to define the scope of SKOS, and specifically to define the requirements for coneying information required to construct an alphabetic display:
(Statement 1) The SWDWG MAY publish an algorithm to generate a default thesaurus alphabetic display from an RDF graph using the SKOS vocabulary. However, applications are not required to use the algorithm, and MAY use any means to convey information required to construct a thesaurus alphabetic display.
Thesaurus Systematic Display
From [ISO 2788-1986] section 9.3 ("Systematic Display"):
- A thesaurus in which terms are organized systematically should consist of two parts: a) categories or hierarchies of terms arranged according to their meanings and logical interrelationships; b) an alphabetic index which directs the user to the appropriate part(s) of the systematic section. The link between these two sections is provided by a system of addresses. An address code is assigned to each of the preferred terms in the systematic section, and this code functions as a reference in the alphabetic index...
- ..With this type of display the systematic section is frequently regarded as the main part of the thesaurus, i.e. the part which carries most of the definitional and relational information, in which case the alphabetic index assumes the role of a complementary but secondary component. This is not invariable, however, and thesauri differ widely in their approaches to the relative importance and functions of these two sections, and also in the arrangement and kind of relational information provided in each...
An example of a systematic display:
301 OPTICAL EQUIPMENT 302 CAMERAS RT PHOTOGRAPHY 824 303 MOVING PICTURE CAMERAS By medium 304 CINE CAMERAS 306 TELEVISION CAMERAS
Now, consider the following RDF graph:
# conventional prefixes ex:A skos:prefLabel "OPTICAL EQUIPMENT"@en; skos:narrower ex:B. ex:B skos:prefLabel "CAMERAS"@en; skos:related ex:C; skos:narrower ex:D. ex:C skos:prefLabel "PHOTOGRAPHY"@en. ex:D skos:prefLabel "MOVING PICTURE CAMERAS"@en; skos:narrower ex:E, ex:F. ex:E skos:prefLabel "CINE CAMERAS"@en. ex:F skos:prefLabel "TELEVISION CAMERAS"@en.  rdf:type skos:Collection; rdfs:label "By medium"@en; skos:member ex:E, ex:F.
Given this graph, it is possible to define an algorithm that will generate a default systematic thesaurus display such as the one shown above. However, note that "thesauri differ widely in their approaches to the relative importance and functions of these two sections [systematic and alphabetic], and also in the arrangement and kind of relational information provided in each..." [ISO 2788-1986]
Therefore, the following statement is proposed to define the scope of SKOS, and specifically the requirements for conveying information required to construct a systematic display:
(Statement 2) The SWDWG MAY publish an algorithm to generate a default thesaurus systematic display from an RDF graph using the SKOS vocabulary. However, applications are not required to use the algorithm, and MAY use any means to convey information required to construct a thesaurus systematic display.
Discussion and Implications
Consider the following extract from a systematic display of the Art and Architecture thesaurus:
Styles and Periods <styles and periods by region> <The Islamic World> Saracenic pre-Islamic <Islamic World dynastic styles and periods> Orthodox Caliphate Umayyad Abbasid
If these proposals for limiting the scope of SKOS are accepted, this means that, while an application could use the default algorithm to generate the above systematic display from some SKOS data, it would not be obliged to. It could also convey the systematic display by another means, in parallel to the SKOS data.
This is particularly relevant where indentation and the tree-like layout of a systematic display does not correspond to broader/narrower thesaurus relationships.
For example, the following (from [ISO 2788-1986]) is given as an example of a systematic display where indentation does not convey a broader/narrower relationship:
BOOKS Operations BINDING PRINTING
This is revealed when you consider the corresponding alphabetic display for this thesaurus:
BOOKS RT BINDING RT PRINTING
[ISO 2788-1986] Documentation - Guidelines for the Establishment and Development of Monolingual Thesauri, ISO 2788-1986
[BS 8723-2:2005] Structured vocabularies for information retrieval — Guide — Part 2: Thesauri, BS 8723-2:2005