Commitment class hierarchy

[rjyounes]

• Delete Obligation
• Redefine Commitment - use the word "promise"
• An Agreement is a subclass of Commitment and Collection - a collection of commitments
• Contract: legally binding Agreement
• Rename ContingentObligation to ContingentCommitment
• Keep Offer
• Keep Account - make sure balances don't have to be monetary - e.g., frequent flyer accounts