DAT/DLT Media Information

I am developing a backup standard for our company, systems integration company, but I am not sure how long a DAT or DLT tape is good for.

1. Life Span of each of these tapes?
2. Number of writes/uses that each are good for?
3. Shelf Life e.g. if you have a tape with data on it, sitting on a shelf how long will it retain data?

If any one has information on this or a URL that would be great.

Thanks,

Aaron