Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 11 ■ INDEXES
you could create your own image index. As images are added to the database, your code is
invoked to extract the colors from the images and store them somewhere (wherever you want
to store them). At query time, when the user asks for all “blue images,” Oracle will ask you to
provide the answer from your index when appropriate.
The best example of this is Oracle’s own text index. This index is used to provide keyword
searching on large text items. You may create a simple text index like this:
ops$tkyte@ORA10G> create index myindex on mytable(docs)
2 indextype is ctxsys.context
3 /
Index created.
and then use the text operators the creators of that index introduced into the SQL language:
select * from mytable where contains( docs, 'some words' ) > 0;
It will even respond to commands such as the following:
ops$tkyte@ORA10GR1> begin
2 dbms_stats.gather_index_stats( user, 'MYINDEX' );
3 end;
4 /
PL/SQL procedure successfully completed.
It will participate with the optimizer at runtime to determine the relative cost of using a
text index over some other index or a full scan. The interesting thing about all of this is that
you or I could have developed this index. The implementation of the text index was done
without “inside kernel knowledge.” It was done using the dedicated, documented, and
exposed API. The Oracle database kernel is not aware of how the text index is stored (the APIs
store it in many physical database tables per index created). Oracle is not aware of the processing
that takes place when a new row is inserted. Oracle text is really an application built
on top of the database, but in a wholly integrated fashion. To you and me, it looks just like any
other Oracle database kernel function, but it is not.
I personally have not found the need to go and build a new exotic type of index structure.
I see this particular feature as being of use mostly to third-party solution providers that have
innovative indexing techniques.
I think the most interesting thing about application domain indexes is that they allow
others to supply new indexing technology I can use in my applications. Most people will never
make use of this particular API to build a new index type, but most of us will use the end
results. Virtually every application I work on seems to have some text associated with it, XML
to be dealt with, or images to be stored and categorized. The interMedia set of functionality,
implemented using the Application Domain Indexing feature, provides these capabilities. As
time passes, the set of available index types grows. We’ll take a more in-depth look at the text
index in a subsequent chapter.