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PSH - the Polythematic Structured Subject Heading System - is a controlled dictionary used for the factual description of documents in polythematic collections and for searching for documents in library catalogues. The use of PSH enables the use of the same keywords for the description of documents in libraries, thus enabling the readers to make better use of the catalogues of these libraries, or to create union catalogues. PSH has been conceived as part of a set of selection languages (simultaneous use of UDC and complementation of PSH with keywords for detailed document description are planned).
PSH contains keywords in 42 sections (section General plus scientific fields). A keyword is followed by a two-letter abbreviation of a section.
The General section includes terms for processes and phenomena, which can be used in various branches and fields, which, if combined with concrete terms, enable for the description of documents.
Keywords are hierarchically structured on six levels.
The hierarchical structure does not copy the structure of scientific fields. It should only reflect the focus of the published literature and structure of library collections.
The relation between the keywords is a thematic one, not fixed hierarchical relation (so- called technological hierarchy).
Each keyword can be used only once, basic scientific fields are filed in the following order: mathematics, physics, chemistry, biology.
Documents are described using a combination of relevant keywords, regardless of section.
PSH does not contain geographic, chronological and personal keywords, product names, names of organizations and professional groups. These keywords are stored in appropriate UNIMARC fields.
Natural word order is used. When using multiple adjectives, additional adjectives follow the substantive.
Standard Czech language is used.
The keyword must be expressed using the minimum number of words possible.
From Czech and foreign terms, the more common term, expert term, or a linguistically more appropriate term is used.
Terms more commonly used in the given field are preferred whenever there is a choice from more spelling alternatives (conservative/more progressive); a single alternative is used within a single field.
Multiword commonly used terms are not divided.
Keywords, which can be created by joining existing keywords, are not included.
Nominal forms are preferred.
Countable nouns are listed in plural nominative, abstract and uncountable nouns in singular
nominative.
Abbreviations are preferably not used.
When introducing new keywords, they should be as general as possible. PSH should not contain very detailed keywords.
Individual sections should be balanced.
It is not recommended to unnecessarily change the structure and move keywords from one section to another, stability is more important than attempts at improving details.
Associating references (see also:) join related keywords.
Disjunctive references (see:) refer from synonyms or unused subordinate term to the keyword used.
It is not necessary to refer to the closest superior/inferior keywords or to keywords on the same hierarchical level.
PSH is intended for the description of documents. The need for suggested new keywords should be verified by checking the frequency of their occurrence in literature.
Each keyword appears only once in the PSH, even if it is related to more fields. Thus the whole structure is interconnected by associative links, linking logically associated keywords in various parts of the database. Over 4,500 such associative links are used in the current version of PSH. Synonyms and keywords having partially the character of synonyms are interconnected by approx. 2,700 disjunctive links.
The limitation to 6 (7) logical levels of PSH enables specialized libraries to expand the database with further levels, which the PSH cannot encompass due to its universal character.
PSH has been designed for the implementation into automated library systems. When using suitable software (which can also be obtained together with the data file), PSH can also be used independently as a source of keywords for factual description within any library.
At the STL, PSH is one of the search tools used for searching in the online library catalogue. An overview of the structure of the database can also be found at the Czech Technical University Computing Centre website.
We will welcome any comments, questions, wishes and especially comments related to the use of the PSH at:
State Technical Library
PSH Section
Mariánské nám. 5
P.O.B. 206
110 01 Praha 1
Czech Republic
fax: + 420 222 221 340
phone:: +420 221 663 465
e-mail: psh@stk.cz