... Up: Data Archives . ... The Data Archive and Distribution System (DADS) manages the Hubble Data Archive (HDA), a WORM Optical Disk Archive which contains over two terabytes of Hubble Space Telescope data. ... We describe a system which uses the database request logs as input to a flexible cache model. ... The Cache Model consists of three major components. ... The model provides the basis for an operational cache index since it uses the same data as DADS uses to obtain datasets from optical disks. ...