The investment seeks to track the investment results of the Bloomberg Barclays U.S. CMBS (ERISA Only) Index. The index measures the performance of investment-grade commercial mortgage-backed securities (CMBS), which are classes of securities (known as certificates) that represent interests in pools of commercial mortgages. The fund generally will invest at least 90% of its assets in the component securities of the underlying index and may invest up to 10% of its assets in certain futures, options and swap contracts, cash and cash equivalents.