Extensional predicates

Extensional predicates are input data for a Datalog program.

Declared like this:

extensional pokemon(id: integer, name: string, hp: integer).

Intuitively: pokemon lists the name and hp for each Pokémon, identified by an integer id.

• Extensionals model the entities we work with (here: Pokémon), often referenced by unique integer IDs.
• They form the extensional database (EDB) the program runs on; different runs may use different EDBs.
• We’ll look at an extensional two ways: as a table (database view) and a set of facts (deductive view).