The general rule for capital cost allowance is that the CCA rates track the useful life of the asset. The rate that is associated with any asset will depend on how long it's expected to last. The rate on a building would be lower than the rate on a computer, for example. Each one of these classes has its own rate, ranging from some very low—I think down to 2%—up to 100% capital cost allowance rates.
The accelerated investment incentive increases the rate that can be taken and allows more deductions to be taken earlier in a lot of cases, in addition to the base rate that basically reflects the useful life of the assets.