Module 5 - Subject access to information

Module 5 - providing subject access to information

Providing subject access appropriate to the needs of users is key to providing effective access to resources.The OPAC seeks to provide access to he subject of the information resources represented in the system.

Vocabularies whether uncontrolled or uncontrolled = indexing language

Subject access tools spectrum/subject approaches

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  rely on uncontrolled vocabularies (derived indexing) - full text searching & searching of text in surrogate record [derives from the document]. This natural language approach uses OPAC to search for words/phrases appearing anywhere within a catalogue record (or within title or notes fields). Requires little or no intellectual input from cataloguer - vocabulary already present so concepts don't have to be matched with appropriate terms from controlled vocabularies. Weaknesses - lack of control over vocabulary more intellectual effort is required by the searcher. Exhaustively - may lead to loss of precision.
  
  
• highly controlled vocabularies (assigned indexing) - such as subject headings or thesaurus, & classification schemes [takes words from somewhere else and assigns them to the document] assigned by cataloguer. Words/phrases are selected  to denote a subject - assigned to resources on the subjects they describe. Provide standardisation and enable consistent use of terms to describe each subject. Weaknesses - need regular updating to remain relevant and current to provide effective subject access. Takes time expertise to master.

• 
  
  
  combination of assigning traditional controlled vocabularies and uncontrolled vocabularies (natural language terms) derived from the information resource (and metadata provided by the sources of the resource - author, publication etc).
  This third approach is most appropriate to school libraries - as both controlled vocabularies and natural language approaches are considered as having value an being able to complement each other. 
  
  
  

  Process of providing subject access using the combination approach to provide access
  
  
  Step 1 - determine what the information resource is about - its subject (aboutness).
  
  Step 2 - assign terms from controlled vocabulary (thesauri, classification scheme) that best represents the resource's aboutness. 
  Be wary of exhaustivity - the level of detail cataloguer's go in providing subject access. Exhaustivity subject indexing involves the selection of large numbers of items and attempts to cover all of the subject of the information resource.  
  Summarising - where the main subjects are indicated by a limited number of terms from the controlled vocabulary - often 4-5 terms depending on the document. 
  
  Step 3 - after assigning a number of single concepts to describe a subject (step 2) we can do ONE of two things.
  a) index the single concepts as they separate terms
  b) combine several concepts into one term (pre-coordination). 
  
  
  Pre-coordination - occurs at the indexing stage
  Post-coordination - occurs at search stage
  
  
  Most controlled vocabularies used in libraries, subject headings or classification schemes, are pre-coordinated.
  
  
  Step 4 - Derived indexing - determine other attributes of the resource to search on. Select only words that are already present in the information resource (commonly title and abstract) and then provide a means of searching these words. 
  
  
  

  Full-text searching 5.4

  • derived indexing that is the least controlled and searches entire documents for that key/subject word. Search engines are commonly used to find resources on particular topics.
  • Yields many results (recall) but the accuracy of the match (precision) is minimal. Often keywords entered in full-text searching is too broad. 
  • Synonyms, alternative spellings and homonyms have an impact on what we retrieve when using full-text searching.
  • To minimise irrelevant or limited results specify variant spellings and alternative words.

  
   Searching of text in resource descriptions 5.5
  

  • abstracts or catalogue records (keyword searching of SCIS record)
  • Provide more control over the vocabulary that is searched  

   

  Searching on title keywords 5.6

  • not a good search option if you want precision in search terms - produces many results most of which are not useful or relevant
  • it is faster than carrying out a full-blown searching using a thesaurus or subject headings list
  • not as reliable as searching abstracts
  • often used by library users when searching OPACs