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SharePoint search: more insights

Surprisingly this white paper on building multilingual solutions in SharePoints provides a good overview of how the search works, regardless of whether you are interested in the multilingual aspect.

White paper: Plan for building multilingual solutions.

Read page 15, titled “overview of the language features in search” for a description of content crawling and search query extraction. Then 16-18 provide a good overview of individual features and what they are doing.

Word breakers A word breaker is a component used by the query and index engines to break compound words and phrases into individual words or tokens. If there is no word breaker for a specific language, the neutral word breaker is used, in which case word breaking occurs where there are white spaces between the words and phrases. At indexing time, if there is any locale information associated with the document (for example, a Word document contains locale information for each text chunk), the index engine will try to use the word breaker for that locale. If the document does not contain any locale information, the user locale of the computer the indexer is installed on is used instead. At query time, the locale (HTTP_ACCEPT_LANGUAGE) of the browser from which the query was sent is used to perform word breaking on the query. Additional information about the language availability of the word breaker component is available in Appendix B: Search Language Considerations.

Stemming Stemming is a feature of the word breaker component used only by the query engine to determine where the word boundaries are in the stream of characters in the query. A stemmer extracts the root form of a given word. For example, ”running,” ”ran,” and ”runner“ are all variants of the verb ”to run.” In some languages, a stemmer expands the root form of a word to alternate forms. Stemming is turned off by default. Stemmers are available only for languages that have morphological expansion; this means that, for languages where stemmers are not available, turning on this feature in the Search Result Page (CoreResult Web Part) will not have any effect. Additional information about language availability for the Stemmer feature is available in Appendix B: Search Language Considerations.

Noise words dictionary Noise words are words that do not add value to a query, such as ”and,” ”the,” and ”a.” The indexing engine filters them to save index space and to increase performance. Noise word files are customizable, language-specific text files. These files are a simple list of words, one per line. If a noise word file is changed, you must perform a full update of the index to incorporate the changes. Additional information about the noise words dictionary and how to customize it is available at www.microsoft.com.

Custom dictionary The custom dictionary file contains values that the search server must include at index and query times. Custom dictionary lists are customizable, language-specific text files. These files are used by Search in both the index and query processes to identify exceptions to the noise word dictionaries. A word such as “AT&T,” for example, will never be indexed by default because the word breaker breaks it into single noise words. To avoid this, the user can add ”AT&T” to the custom dictionary file; as result, this word will be treated as an exception by the word breaker and will be indexed and queried. These files contain a simple list of words, one per line. If the custom dictionary file is changed, you must perform a full update of the index to incorporate the changes. By default, no custom dictionary file is installed during Office SharePoint Server 2007 Setup. Additional information about the custom dictionary file and how to customize it is available at www.microsoft.com.

Thesaurus There is a configurable thesaurus file for each language that Search supports. Using the thesaurus, you can specify synonyms for words and also automatically replace words in a query with other words that you specify. The thesaurus used will always be in the language of the query, not necessarily the server’s user locale. If a language-specific thesaurus is not available, a neutral thesaurus (tseneu.xml) is used. Additional information about the thesaurus file and how to customize it is available at www.microsoft.com.

Language Auto Detection The Language Auto Detection (LAD) feature generates a best guess about the language of a text chunk based on the Unicode range and other language patterns. Basically, it’s used for relevance calculation by the index engine and in queries sent from the Advanced Search Web Part, where the user is able to specify constraints on the language of the documents returned by a query.

Did You Mean? The Did You Mean? feature is used by the query engine to catch possible spelling errors and to provide suggestions for queries. The Did You Mean? feature builds suggestions by using three components:

· Query log Information tracked in the query log includes the query terms used, when the search results were returned for search queries, and the pages that were viewed from search results. This search usage data helps you understand how people are using search and what information they are seeking. You can use this data to help determine how to improve the search experience for users.

· Dictionary lexicon A dictionary of most-used lexicons provided at installation time.

· Custom lexicon A collection of the most frequently occurring words in the corpus, built at query time by the query engine from indexed information.

The Did You Mean? suggestions are available only for English, French, German, and Spanish.

Definition Extraction The Definition Extraction feature finds definitions for candidate terms and identifies acronyms and their expansions by examining the grammatical structure of sentences that have been indexed (for example, NASA, radar, modem, and so on). It is only available for English.

Written by Karen

September 30th, 2009 at 6:56 am

Posted in search,sharepoint