Page 91 - DLIS405_INFORMATION_STORAGE_AND_RETRIEVAL

Information Storage and Retrieval

Notes Self Assessment

Multiple Choice Questions:
1. Key trends in indexing include ...... indices.
(a) Chinese (b) European
(c) Islamic (d) African
2. Clark said, market participants generally feel that the very few indices out there which
represent all ...... market are not very good.
(a) Two (b) Three
(c) Four (d) One
3. Index providers can reduce such an index to ...... stocks, with the same basic return and
Fairly good correlation, said clark.
(a) 30 (b) 40
(c) 50 (d) 60

9.1 Derived Indexing

Derived indexing terms are terms occurring in the text to be indexed. Assigned terms are terms not
occurring in the text.
“There are essentially two approaches to the creation and maintenance of this document or
knowledge representation. One is to create a knowledge system in advance and assign the documents
to it afterward: assigned indexing. The other is to derive the terms of the index language from the
documents themselves: derived indexing.
The manual library systems, in which books were classified according to an existing classification
system, for example, Dewey or UDC, are assigned indexing systems; computerized IR-systems which
extract keywords from the documents according to a weighting scheme are typically derived indexing
systems. We will extend the definition of assigned indexing systems to contain all systems that use
terms in their docreps (document representations) that are not taken from the documents themselves,
because such external terms belong to a knowledge representation outside the document.
The derived indexing systems became very popular when the computer made it easy to create an
inverted list of all the words occurring in a document base. In the 1970s and ’80s much effort was
put into the development of techniques to identify such words (phrases, sentences) in the inverted
lists as were most efficient in retrieving particular documents.
Assigned terms may come from external semantic resources (e.g., authority files, classification systems
or thesauri) or other kinds of external information.
Derived indexing systems are generally more primitive compared to assigned systems (or, of course,
combinations). It is easy mechanically to mark a text for words to appear in an index, and to construe
an index on this basis. However, users searching for a concept using a synonymous term, a broader
term or a narrower term, will miss the information. This is the rationale behind controlled
vocabularies.

Explain Derived Indexing.
It is common to classify documents according to an organization of disciplines. Documents may or
may not describe their disciplinary memberships. Even if they do, the authors’ organization of
disciplines may be different from those chosen to be assigned by a library or an information system.

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