I dont understand the concept of risk decomposition. are we breaking the return of a portfolio and attributing it to various risk factors and then calculating VaR for each risk factor.
The first step of every VaR calculation, regardless of the VaR method used, is to
convert the set of holdings in the portfolio into a set of exposures to risk factors, a process called risk decomposition. In some instances, this process can be very simple an equity security can be the risk factor itself. In other instances, the process can be highly complex. For example, a convertible bond issued by a foreign entity has both currency and equity risk factors as well as exposures to multiple points on a yield curve of a given credit quality. Fixed-income instruments and derivative products often contain distinct risk exposures that require decomposition in order to accurately capture their loss potential.