The text trigger mechanism allows implementing a broad range of
content tracking functionality. The idea is storing free text or
XPATH queries in association to a text indexed column of a table.
When the content of the table changes through inserts or updates,
the new data is matched against a base of stored queries and hits
are marked into a separate table. The data being tracked may either
be plain text or XML. In the event of XML, both free text and XPATH
queries can be stored.
The benefit of the text trigger system as opposed to other forms
of periodic content tracking is that the incoming data itself
indexes a base of stored queries instead of a base of stored
queries repeatedly indexing the database. This means that only the
changes are compared to the stored queries and that queries that
could not even in principle match will not be tried. This results
in a qualitatively better performance and scalability than
repeatedly running a batch of queries over updated data and thus
makes possible personalized information filtering applications that
would be impractical with other approaches.