Strength of schedule is calculated from the opponents projected fantasy points allowed for the DB position. The best rating is +16 which gives the player the advantage against the defense and indicates an easy opponent, the worst rating is -16 which gives the defense the advantage and indicates a tough opponent.
Claiborne didn't post huge numbers in his rookie season, but there's considerable reason for optimism in 2013. Claiborne is a physical player whose skill-set would seem to mesh well with Monte Kiffin's Tampa-2 defense in Dallas. That's a scheme that spurred Ronde Barber on to many solid IDP seasons, and fantasy owners looking for an upside cornerback in leagues that require the position should keep Claiborne on their draft-day radar.