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For example: | Kidney stone | and | Renal calculus | are synonymous Descriptions in SNOMED CT. However, a search of SNOMED CT for the target phrase "kidney stone fragmentation" yields the result | Percutaneous nephrostomy with fragmentation of kidney stone | while a search for "Renal stone fragmentation" yields no results. One way of addressing this problem is to maintain a table of word equivalents, and a table of this type is a prerequisite for exhaustive synonym generation. The Word Equivalent Table is included in the Developer Toolkit of SNOMED CT. [see SNOMED CT Developer Toolkit Guide]. Individual can be found in the Lexical Resources folder, which is available from the  Technical Resources in the Document Library. Individual implementers will wish to add additional word equivalents to meet the requirements of their particular medical specialty or user needs. The resulting table then acts as an additional resource to assist searching and parsing of phrases. It need not be a comprehensive dictionary of words.

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A system user enters the search string "Fragmentation of renal calculus;" the search returns no results. The search application that the user has been provided with has the option to extend the search by using the word equivalents table (see 

Word Equivalents Table Example

Extending searches with word equivalents - step 1

The user selects this option (or it is invoked automatically because the initial search without word equivalents found nothing) and searches again using the same search string. The table is used to make substitutions in the search string to produce all possible unique search variants: 

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These 8 search variants are used as the target phrases for the searches. The search results of these variants are combined, duplicate Concepts are eliminated and the list of search results is returned.

Extending searches with word equivalents - step 2

For more information on the the search support tables provided by SNOMED International, please see  6.1.5 Search Support Tables.