index created for use as a table

Hi,

I've read somewhere, that Oracle offers a feature, that I can create a table as a index.
i.e. I've a table with key1,key2,key3,key4,value where key1,key2,key3,key4 represents a unique index. Then it would be possible not to create the table and the unique index, but create only the index and add the field "value". But I didn't find again the website/news-item I've read. Does anybody know that feature?

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Best regards
Dietmar Brueckmann