Terminology

• Algorithm (physical version of logical op)
• Enforcer (physical op with no equivalent logical op)
  .g. Sort used to derive required physical properties
• Property function (for logical op, algorithm, enforcer) tells you preperties of result
• Physical Properties: equality function, 'covers' function e.g sort on (r.A, r.B) covers sort on (r.A)
• Applicability function: gives required physical property of input to algorithm / enforcer.