Bond Spread Calculations

Implements five spread methodologies for fixed income analytics with Bloomberg YAS parity and data-source neutral architecture.

Spread Hierarchy (Simplest → Most Complex)

Spread	What It Measures	Complexity	Curve Required
G-Spread	Yield over interpolated government bond	Low	Gov't par curve
I-Spread	Yield over interpolated swap rate	Low	Swap par curve
Z-Spread	Constant spread over zero curve matching dirty price	Medium	Zero/spot curve
ASW	Spread in swap market terms	Medium	Zero + forward curves
OAS	Spread after removing embedded option value	High	Zero + vol surface

Typical ordering: OAS ≤ Z-Spread ≈ ASW < I-Spread < G-Spread for investment-grade bonds.