The article tackles the assignment of UDC numbers to the documents for the research field of wood technology in the Slovenian union bibliographic/catalogue database Cobib.si, search possibilities with the UDC and relationship of UDC with selected subject headings. We identified the mostimportant UDC numbers related to wood technology. We assessed the frequency of assignment of particular numbers by way of MARC-based prefixes DC= (MARC/Comarc subfield 675a) and UC= (MARC/Comarc subfield 675c). We assessed the co-occurrence of different groups of UDC, relation to the document types and Slovenian- language documents, as well as the co-occurrenceof UDC with wood- or wood-technologies-related Slovenian language subject headings. We tested the most applicable search syntax. Subfields 675a and 675c differ in the content of UDC. The 675c is based on a special authority-list and does not sufficiently provide narrower, more specific numbers in relation to wood. Two groups (630*8* and 674*) are assigned with a very high frequency. These groups can be represented in both subfields. Frequently, the two subfields contain UDC from different groups, soin order to achieve optimal retrieval recall it is necessary to use both subfields, by way of Boolean OR. Analysis of co occurrence of UDC (based on 674* and 630*8*), and subject headings (based on Slovenian-language stem for wood) shows that many documents (35 % and 34%, respectively) do not contain subject headings based on the term wood.
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