When used in the ORDER BY
clause of a CBR query, the Rank property permits you to return objects in order of search relevance. IBM® Content Search Services calculates the value of the Rank property for each returned object based on factors such as term instance frequency.
For detailed information about the ranking factors, see CBR queries using IBM Content Search Services. In accordance with these factors, changes to the following items can affect the Rank property value for a returned object:
AUTO
for automatic language identification. For some objects, automatic language identification can misidentify the text language. If you change the text language from AUTO
to en
(English) and reindex an object with a misidentified text language, word stems are now indexed. For example, if the object text includes the word lions, the stem lion is also indexed. Because of ranking factors such as term instance frequency, the addition of new indexed text affects Rank property values. Also, changing the text language can affect the interpretation of the search expression: the stems for the search terms might now be functionally included in the expression. Because of ranking factors such as term inverse matched-object frequency, term presence ratio, and term boosting, indirect changes to the search expression affect Rank property values.
Consequently, the Rank property value for a returned object can change depending on when you run a query. The property value can change without changing the ranking of the object relative to other returned objects.
Related reference
For information about query syntax and using the Rank property in a query, see CBR query syntax introduction. For information about the Indexing Language property, see Object store properties (CBR IBM Search tab).
Related concepts
For information about word stems, see Word stems. For information about stop words, see Stop words. For information about synonyms, see Synonyms.