Block-based allocation and Extent-based allocation in Solaris

Hi guys!

Could you tell me what's this figure about? (See the attached figure below.)
This is a representation of block allocation filesystem and extent allocation filesystem in Solaris.

Does this mean that in a block-based allocation, data are placed in individual blocks while in extent-based allocation, each block has many blocks inside it?
Am I correct?

Please someone correct me if I got it wrong.
Thanks!