Article X, § 11 of the Constitution of Virginia requires the General Assembly to maintain a retirement system for state employees and employees of participating political subdivisions and school divisions, subject to restrictions and conditions prescribed by the General Assembly, that shall be administered in the best interests of the beneficiaries thereof. To that end and for the purposes of providing adequate benefits and pensions to members, encouraging stable employer contribution rates, and ensuring the overall soundness of the Retirement System, the General Assembly hereby establishes the Virginia Retirement System as an independent agency of the Commonwealth, exclusive of the legislative, executive, and judicial branches of government, in the following provisions.