Per Ahlgren

1
On a cognitive search strategy

• Per Ahlgren

2
Overview

• Background
• Ingwersens example
• A cognitive search strategy
• Search formulation construction
• Four situations but two search formulations
• A remedy
• Concluding remarks

3
Background

• Important to provide users of the digital library
  with tools that help them to retrieve information
  relevant to their needs
• Search stratgies - approaches for search problems
• Example. The building blocks strategy

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Ingwersens example

• Two terms, A and B
• Two fields, title field (TI) and
  descriptor/identifier field (DE,ID)
• Four atomic search formulations
• A/TI A/DE,ID B/TI B/DE,ID
• Assumed situation with regards to document
  frequency (df) df (A/TI) lt df (B/TI) lt df
  (A/DE,ID) lt df (B/DE,ID).

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• Principle (P) - atomic search formulations with
  lower frequencies should be combined before
  formulations with higher frequencies
• Idea behind P a terms value for retrieval
  purposes is inversely proportional to the number
  of documents in which the term occurs

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A cognitive search strategy

• Different cognitive agents - author (TI) and
  indexer (DE,ID) - are involved with regards to
  the assignment of terms to documents
• Occurrence of different cognitive agents
• Cognitive overlap
• When constructing Boolean search formulations in
  a two term TI/DE,ID search, consider the factors
  occurrence of different cognitive agents and
  cognitive overlap when combining atomic
  formulations with the AND operator

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• Optimal situation both terms are present in both
  fields (the cognitive agents involved agree about
  the two access points). Expressed by the
  following formulation A/TIB/TIA/DE,IDB/DE,ID.
• A multiple evidence approach - the strategy
  combines evidence for the relevance of a document

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Search formulation construction

• Purpose stepwise retrieval of a number of
  subsets of the set D of documents that is
  retrieved by AB. First formulation S1
  A/TIB/TIA/DE,IDB/DE,ID.
• Two methods
• (1) NOTPRESET (Ingwersens method)
• A new formulation is obtained by (1) combining
  atomic formulations by the AND operator,
  considering the factors (a) presence of A and B,
  (b) occurrence of different cognitive agents and
  (c) document frequency, (2) excluding all the
  preceeding formulations by the NOT and OR
  operators, and (3) ANDing the results of (1) and
  (2).

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• Should be fairly easy for the user to grasp
• Example. S2 A/TIB/TIA/DE,ID NOT S1
• (2) NOTATOMIC
• A new formulation is obtained by (1) combining as
  many atomic formulations as possible (in the
  light of earlier formulations) by the AND
  operator, considering the factors (a) presence of
  A and B, (b) occurrence of different cognitive
  agents and (c) document frequency, (2) excluding
  by the NOT and OR operators all the atomic
  formulations that are not part of the result of
  (1), and (3) ANDing the results of (1) and (2).
• Yields, in most cases, shorter fomulations than
  NOTPRESET

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• Should be fairly easy for the user to grasp
• Is abandoned in step 10 and step 11
• Example. (2) A/TIB/TIA/DE,ID NOT B/DE,ID
• Presence of A and B the most importent factor
• Occurrence of different cognitive agents more
  important than document frequency

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Four situations but two search formulations

• Consider the (NOTATOMIC) formulations
• (10) A/TI NOT (B/TIB/DE,ID) and
• (11) B/TI NOT (A/TIA/DE,ID).
• (10) and (11) are indefinite with respect to
  A/DE,ID and B/DE,ID, respectively.

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• (1) A is present in TI but not in DE,ID, and B is
  absent from both fields
• and
• (2) A is present in both fields, and B is absent
  from both fields,
• or between
• (3) B is present in TI but not in DE,ID, and A is
  absent from both fields
• and
• (4) B is present in both fields, and A is absent
  from both fields.

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• We then need four formulations instead of (10)
  A/TI NOT (B/TIB/DE,ID) and (11) B/TI NOT
  (A/TIA/DE,ID) (instead of S10 and S11), four
  formulations that express the four situations.
• Ingwersens formulations express only 11 of the
  16 possible situations with regards to the
  presence of A and B in the two fields.

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Figure 1 The 16 possible situations with regards
to the presence of of A and B in the two fields.
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A remedy

• NOTATOMIC
• Subtitute the following four formulations (in the
  given
• order)
• 9a A/TIA/DE,ID NOT (B/TIB/DE,ID)
• 9b B/TIB/DE,ID NOT (A/TIA/DE,ID)
• 10 A/TI NOT (A/DE,IDB/TIB/DE,ID)
• 11 B/TI NOT (B/DE,IDA/TIA/DE,ID)
• for
• (10) A/TI NOT (B/TIB/DE,ID)
• and
• (11) B/TI NOT (A/TIA/DE,ID).

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• The new set of formulations express 15 of the 16
  possible cases with regards to the presence of A
  and B in the two fields, not just 11.
• NOTATOMIC is not abandoned.

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• NOTPRESET
• It is also possible to use a special case of
  NOTPRESET, say NOTPRESET, to construct
  formulations that express the four situations in
  question. When constructing a new formulation,
  the first step in NOTPRESET is identical with
  the first step in NOTATOMIC combine as many
  atomic formulations as possible (in the light of
  earlier formulations) by the AND operator,
  considering the factors presence of A and B,
  occurrence of different cognitive agents and
  document frequency.

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• The new set of formulations express 15 of the 16
  possible cases with regards to the presence of A
  and B in the two fields, not just 11.

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Concluding remarks

• Ingwersens set of formulations should be
  modified to correspond to 15 of the 16 possible
  situations with regards to the presence of the
  terms A and B in the two fields.
• Ingwersens approach gives the Boolean searcher a
  hint concerning the order in which the parts of a
  (possibly large) document set should be
  retrieved.

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• If the command language does not admit
  abbreviation of an OR formlation, NOTATOMIC is in
  my opinon preferable to NOTPRESET.