| Oracle® Text Reference 10g Release 1 (10.1) Part Number B10730-01 |
|
|
View PDF |
| Oracle® Text Reference 10g Release 1 (10.1) Part Number B10730-01 |
|
|
View PDF |
This appendix describes stopword transformations. The following topic is covered:
When you use a stopword or stopword-only phrase as an operand for a query operator, Oracle Text rewrites the expression to eliminate the stopword or stopword-only phrase and then executes the query.
The following section describes the stopword rewrites or transformations for each operator. In all tables, the Stopword Expression column describes the query expression or component of a query expression, while the right-hand column describes the way Oracle Text rewrites the query.
The token stopword stands for a single stopword or a stopword-only phrase.
The token non_stopword stands for either a single non-stopword, a phrase of all non-stopwords, or a phrase of non-stopwords and stopwords.
The token no_lex stands for a single character or a string of characters that is neither a stopword nor a word that is indexed. For example, the + character by itself is an example of a no_lex token.
When the Stopword Expression column completely describes the query expression, a rewritten expression of no_token means that no hits are returned when you enter such a query.
When the Stopword Expression column describes a component of a query expression with more than one operator, a rewritten expression of no_token means that a no_token value is passed to the next step of the rewrite.
Transformations that contain a no_token as an operand in the Stopword Expression column describe intermediate transformations in which the no_token is a result of a previous transformation. These intermediate transformations apply when the original query expression has at least one stopword and more than one operator.
For example, consider the following compound query expression:
'(this NOT dog) AND cat'
Assuming that this is the only stopword in this expression, Oracle Text applies the following transformations in the following order:
stopword NOT non-stopword => no_token
no_token AND non_stopword => non_stopword
The resulting expression is:
'cat'
| Stopword Expression | Rewritten Expression |
|---|---|
| stopword | no_token |
| no_lex | no_token |
The first transformation means that a stopword or stopword-only phrase by itself in a query expression results in no hits.
The second transformation says that a term that is not lexed, such as the + character, results in no hits.
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword AND stopword | non_stopword |
| non_stopword AND no_token | non_stopword |
| stopword AND non_stopword | non_stopword |
| no_token AND non_stopword | non_stopword |
| stopword AND stopword | no_token |
| no_token AND stopword | no_token |
| stopword AND no_token | no_token |
| no_token AND no_token | no_token |
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword OR stopword | non_stopword |
| non_stopword OR no_token | non_stopword |
| stopword OR non_stopword | non_stopword |
| no_token OR non_stopword | non_stopword |
| stopword OR stopword | no_token |
| no_token OR stopword | no_token |
| stopword OR no_token | no_token |
| no_token OR no_token | no_token |
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword ACCUM stopword | non_stopword |
| non_stopword ACCUM no_token | non_stopword |
| stopword ACCUM non_stopword | non_stopword |
| no_token ACCUM non_stopword | non_stopword |
| stopword ACCUM stopword | no_token |
| no_token ACCUM stopword | no_token |
| stopword ACCUM no_token | no_token |
| no_token ACCUM no_token | no_token |
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword MINUS stopword | non_stopword |
| non_stopword MINUS no_token | non_stopword |
| stopword MINUS non_stopword | no_token |
| no_token MINUS non_stopword | no_token |
| stopword MINUS stopword | no_token |
| no_token MINUS stopword | no_token |
| stopword MINUS no_token | no_token |
| no_token MINUS no_token | no_token |
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword NOT stopword | non_stopword |
| non_stopword NOT no_token | non_stopword |
| stopword NOT non_stopword | no_token |
| no_token NOT non_stopword | no_token |
| stopword NOT stopword | no_token |
| no_token NOT stopword | no_token |
| stopword NOT no_token | no_token |
| no_token NOT no_token | no_token |
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword EQUIV stopword | non_stopword |
| non_stopword EQUIV no_token | non_stopword |
| stopword EQUIV non_stopword | non_stopword |
| no_token EQUIV non_stopword | non_stopword |
| stopword EQUIV stopword | no_token |
| no_token EQUIV stopword | no_token |
| stopword EQUIV no_token | no_token |
| no_token EQUIV no_token | no_token |
|
Note: When you use query explain plan, not all of the equivalence transformations are represented in the EXPLAIN table. |
| Stopword Expression | Rewritten Expression |
|---|---|
| non_stopword NEAR stopword | non_stopword |
| non_stopword NEAR no_token | non_stopword |
| stopword NEAR non_stopword | non_stopword |
| no_token NEAR non_stopword | non_stopword |
| stopword NEAR stopword | no_token |
| no_token NEAR stopword | no_token |
| stopword NEAR no_token | no_token |
| no_token NEAR no_token | no_token |
| Stopword Expression | Rewritten Expression |
|---|---|
| stopword * n | no_token |
| no_token * n | no_token |
|
 Copyright © 2003 Oracle Corporation All Rights Reserved. |
|
