Datalog

• The basic language we have seen so far is a constraint language with:
  • Variables,
  • Constants (the domain of the constraint system),
  • Atoms (user predicates),
  • And a unique constraint $=/2$ which expresses equality between constants
• There are no data structures, and the control flow is not specified
• This language, plus
  • Numbers
  • Arithmetic operations
  • Some other facilities
  is often used in advanced data bases
• Basic operations of relational data bases easily expressed!