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The performance of single keyword searches is highly dependent on the number of candidate returned by the keyword for subsequent filtering. The extremely high number of matches for some words in common use makes it likely that some searches will be unacceptably slow.

One way to alleviate this problem would be to create a table containing a row for all combinations of word pairs in each . In some database environments that support optimization of multiple key searches, this may offer no benefits. However, in other environments, such a table may substantially speed searches.

A comprehensive word pair table would be very large. Such a table covering the full content of would contain approximately 1.5 million unique word pairs and 6 million rows. Limiting the unique keys to the first three letter of each word reduces the table size to a more readily optimized set of keys. This requires the final part of the search to be conducted using text comparison (since the keys are incomplete).

Generating the DualKey index

Although Dualkey indexes are available as part of the Developer Toolkit , it is important to know how this table is generated. users that generate should follow the method outlined below to generate new entries in the Dualkey index, based on the in the .

For each , parse the text of the term :

  • To avoid inappropriate case mismatches, convert all characters to the same case;
  • Extract words by breaking at spaces, punctuation marks, and brackets;
  • For each word of three characters or more that is not in the list of excluded words, extract the first 3 characters, and arrange the word fragments in alphabetical order ;
  • Generate the dual keys for this

    by concatenating each word fragment with those that come after it in the list;
  • For each dual key, add a row to the word pair tables.

Example: Generation of keywords for a sample Description

Table 36. Sample Description

 

 

 

Term

19954002

Total replacement of hip with use of methyl methacrylate

  • To avoid inappropriate case mismatches, convert all characters to the same case.

"TOTAL REPLACEMENT OF HIP WITH USE OF METHYLE METHACRYLATE"

  • Extract words by breaking at spaces, punctuation marks, and brackets.
  1. TOTAL;
  2. REPLACEMENT;
  3. OF;
  4. HIP;
  5. WITH;
  6. USE;
  7. OF;
  8. METHYLE;
  9. METHACRYLATE.
  • For each word of three characters or more, that is not in the list of excluded words, extract the first 3 characters, and arrange the word fragments in alphabetical order .
  1. HIP;
  2. MET;
  3. REP;
  4. TOT;
  5. USE.

Note:

"OF" is less than 3 characters and is an excluded word, "WITH" is an excluded word and "MET" is duplicated, so we only include it once.

  • Generate the dual keys for this

    by concatenating each word fragment with those that come after it in the list;
  • For each dual key, add rows to the word pair tables.

    Table 37. DescDualKey

     

    Dual key

    HIPMET

    HIPREP

    HIPTOT

    HIPUSE

    METREP

    METTOT

    METUSE

    REPTOT

    REPUSE

    TOTUSE

    Table 38. ConcDualKey

     

    Dual key

    HIPMET

    19954002

    HIPREP

    19954002

    HIPTOT

    19954002

    HIPUSE

    19954002

    METREP

    19954002

    METTOT

    19954002

    METUSE

    19954002

    REPTOT

    19954002

    REPUSE

    19954002

    TOTUSE

    19954002

    Searching for Descriptions using the DualKey index

    A search on the dual key index can only be carried out if the user enters a search string that contains at least two word fragments both of which are three characters or more in length. If the search string does not meet this criterion, the single keyword search mechanism must be used.
  • The user-typed search string is converted to consistent case;
  • The string is parsed, breaking at spaces and punctuation characters;
  • For each word of three characters or more, extract the first 3 characters, and arrange the word fragments in alphabetical order ;
  • Create a dual key by concatenating the first two 3 letter word fragments;
  • Use this dual key to look up exact matches on the word pair index;
  • found by searching on the word pair index are screened, to see if they contain the complete words in the original search string

Example: Search using word pair index

User searches for "PYRO* 1 OXYGEN*".

  • The string is parsed, breaking at spaces and punctuation characters.
  1. "PYRO*";
  2. 1;
  3. "OXYGEN*".
  • For each word of three characters or more, extract the first 3 characters, and arrange the word fragments in alphabetical order .
  1. "OXY";
  2. "PYR".
  • Create a dual key by concatenating the first two 3 letter word fragments.

OXYPYR


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