In a lecture during my undergraduate degree we were introduced to the race to complete the human genome. Celera were competing with Sanger and collaborators to sequence the human genome. Celera wanted to patent some sequences, whilst Sanger et al. wanted to keep their findings in the public domain. Celera knew they couldn't compete with Sanger et al. with conventional cloning techniques which required a lot of man-power, "so instead opted for shotgun sequencing".
To me it seems like both clone based sequencing and shotgun sequencing could have been used together, however the lecturers semantics were a bit vague (...okay, I wasn't paying close enough attention!) and I didn't ask for clarification at the time.
Whilst I appreciate this is a large topic, what are the main differences between Celera's shotgun sequencing and Sanger's clone based sequencing during the late 1990s? Are "shotgun cloning" and "clone based sequencing" actually mutually exclusive terms?