This appendix focuses on searches using two indexes (or tables), which are included in the SNOMED CT Developer Toolkit. [see SNOMED CT Developer Toolkit Guide] These which can be found in the Lexical Resources folder, which is available from the  Technical Resources in the  Document Library. These indexes are designed to facilitate development of effective search facilities while reducing duplication of effort. Although indexes are available in the Toolkitavailable files, implementers may need to know how to add keyword entries for any locally generated descriptions added as part of an Extension. Please refer to the "Generating the single key index" and "Generating the DualKey index" sub-sections in the Technical Implementation Guide for technical guidance on generating these indexes.

Search Using Single Keyword Index

The DescWordKey table is a single keyword index which is intended to enable searches which are independent of the order in which words appear in a Description. It represents the minimum necessary supporting structure for searches on SNOMED CT content. The single keyword index provides a pointer from each keyword used in any Description, to the Descriptions in which that keyword is used. This table is only useful for applications that utilise the English international release only. Note that some words that are used in Description are stop words, which are unlikely to be in the target of a search. These words are not considered to be keywords and may be excluded from the keyword index.

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• Look up "HIP" on the single keyword index using "starts with" query.

Example results for a Search for "hip"

Descriptions in the search results are converted to consistent case and screened, to see if they contain any words starting with "REPLACEMENT" - only those terms that do are included in the final search results. Using a Dual Key index is more efficient as the same search finds only 11 matches.

Searches involving target words that appear in many Descriptions may be unacceptably slow if searches are carried out using the single keyword index alone. Developers wishing to produce applications with faster search times are encouraged to supplement their system with a multiple keyword index.

Search Using Multiple Keyword Index

The performance of single keyword searches is highly dependent on the number of candidates. Descriptions 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.

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• Description, 1969019, is eliminated since it does not contain the word "1";
• Description, 104951019, is eliminated; it does not contain the word "1" or any word beginning with the string "pyro".