Chapter 8: Verity Topics

Operator precedence rules

The Verity search engine uses precedence rules to determine how operators can be assigned. These rules state that some operators rank higher than others when assigned to topics, and affect how document selections are performed.

Table 8-7 describes how precedence rules apply to operators.

**Table 8-7: Precedence rules**
Operator	Precedence	How precedence is determined
AND OR ACCRUE	Highest precedence	The concept operators take the highest precedence over the other operators. Thus, subtopics of topics using these operators can be assigned any of the operators listed below under “incremental precedence” or “lowest precedence.”
ALL PARAGRAPH SENTENCE NEAR NEAR/N PHRASE ANY	Incremental precedence (in descending order)	The proximity operators refer to incremental ranges that exist within a document. Subtopics of topics using these operators can be assigned their next lowest operator in the precedence order. Thus, a phrase takes precedence over a word; a sentence takes precedence over a phrase or a word; and a paragraph takes precedence over a sentence, a phrase, or a word.
WORD STEM SOUNDEX WILDCARD THESAURUS	Lowest precedence	The evidence operators reside at the lowest level in a topic structure. Because evidence operators are used with words contained in documents, these operators all have the same precedence.

To avoid a precedence violation, do not use ANY or ALL in a parent topic whose child topic includes a concept operator (AND, OR, ACCRUE). Topics that use ANY or ALL cannot have variable weights assigned to them, so you cannot use these operators in a parent topic with any child topic that allows variable weights (such as AND, OR, ACCRUE). Topics using ANY and ALL limit evaluation to present or not present (a score of 0.00 or 1.00). If the criteria are met, the children of these topics get an automatic score of 1.00; if the criteria are not met, the children of these topics get an automatic score of 0.00; so it is not meaningful to assign these children variable weights such as 0.80.

View this book as PDF