This JSON request is using the mnemonic 'IQ_Z_CURVE_ANNUAL_DESC' with GDSPV as a function. This function retrieves an array (a set of values) for the most current availability of content either end of day or intraday. The applicable properties to use with the GDSPV are sector and rating. The output of this metric describes characteristics of the curve itself. The output columns include: 1. Number of Bonds, 2. Number of Credits, 3. Either 'Observed' or 'Derived', 4. Standard Deviation, and 5. Valuation Date.