Using Text Predicates with table aliases

Question

Is there any way to use text predicates with the CONTAINS operator against an event based on a table alias? Just trying to add the function "Contains" to the event struct doesn't work, and reading through the developer's guide, it looks like I need to manually construct an attribute set and add an exf$text attribute for it to work.
The note in the docs says "The attribute sets consisting of one or more text attributes have to be assembled using the ADD_ELEMENTARY_ATTRIBUTE procedure and they cannot be created from an existing object type" and even if I created an attribute set from my table-alias-based event struct and added a new exf$text attribute to it, I can't see how the data would get from the table column into that attribute for evaluation. Is this use case unsupported?

Answer 1

> {quote:title=user10427457 wrote: The reasons why I'm going to all this trouble are because 1) I'd like to keep my rules together and avoid having to have a separate rule class for the text-search rules, and 2) doing an object-based rule where I pass the CLOB in would prevent me from being able to use the CONTEXT index, which enables me to use other operators like WITHIN SENTENCE in my rules.
> }{quote}
Text feature has two types of indexes - CONTEXT and CTXRULE. CONTEXT index is ideal for searching for a document that matches a given query pattern. CTXRULE is used to identify a query pattern that matches a given document. Your application is best suited for CTXRULE and not the CONTEXT index. The Expression Filter automatically uses the CTXRULE index for attributes that are identified as Text attributes (using exf$text). This way you can write a single expression involving scalar attributes as well as text predicates and match them against instances of the event structure. Please read the following chapters for a better understanding of this functionality.
Document classification - CTXRULE:
http://download.oracle.com/docs/cd/B14117_01/text.101/b10729/classify.htm
Expression Filter with CTXRULE:
http://download.oracle.com/docs/cd/B28359_01/appdev.111/b31088/exprn_spatialpred.htm#CHDDBICC
In short, you should be able to create a Text attribute in the object-based event structure and expect the Expression Filter to automatically make use of CTXRULE index when appropriate.
Regards,
-Aravind.