1. A method implemented in a computer system for specifying and enforcing entitlements for performance of financial transactions, the method comprising: in a computer system having at least a processor and memory, providing a hierarchical entitlement structure with inheritance for specifying entitlements for performing financial transactions; receiving user input for defining a plurality of entitlement groups of said hierarchical entitlement structure, wherein each entitlement group has specified permissions to perform financial transactions, limits on performance of said financial transactions, and membership of each user, said hierarchical entitlement structure proving that a given entitlement group inherits permissions provided to its parent entitlement groups in said hierarchical entitlement structure, and wherein defining a plurality of entitlement groups includes restricting permissions inherited by an entitlement group from its parent entitlement group in said hierarchical entitlement structure; in response to a particular user request to perform a financial transaction at runtime, identifying the particular user's membership in a certain entitlement group; and determining whether to allow the particular user to perform the financial transaction based on permissions and limits of said hierarchical entitlement structure applicable to the particular user's performance of the financial transaction.