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A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
thank you for sharing your answer. its also helped me. !
oh realy thanks Ernie for your question... and Xiao thank you for your ans on that topic :)
Xiao Thankx for your answer.