def _execute_program(self, examples: Task, clause: Clause) -> typing.Sequence[Atom]:
"""
Evaluates a clause using the Prolog engine and background knowledge
Returns a set of atoms that the clause covers
"""
if len(clause.get_body().get_literals()) == 0:
return []
else:
self._solver.asserta(clause)
covered_examples = []
pos, neg = examples.get_examples()
total_examples = pos.union(neg)
for example in total_examples:
if self._solver.has_solution(example):
covered_examples.append(example)
self._solver.retract(clause)
# head_predicate = clause.get_head().get_predicate()
# head_variables = clause.get_head_variables()
#
# sols = self._solver.query(*clause.get_body().get_literals())
#
# sols = [head_predicate(*[s[v] for v in head_variables]) for s in sols]
return covered_examples
def _execute_program(self, clause: Clause) -> typing.Sequence[Atom]:
"""
Evaluates a clause using the Prolog engine and background knowledge
Returns a set of atoms that the clause covers
"""
if len(clause.get_body().get_literals()) == 0:
return []
else:
head_predicate = clause.get_head().get_predicate()
head_variables = clause.get_head_variables()
sols = self._solver.query(*clause.get_body().get_literals())
sols = [
head_predicate(*[s[v] for v in head_variables]) for s in sols
]
return sols
def _execute_program(self, clause: Clause, count_as_query: bool = True) -> typing.Sequence[Atom]:
"""
Evaluates a clause using the Prolog engine and background knowledge
Returns a set of atoms that the clause covers
"""
if len(clause.get_body().get_literals()) == 0:
# Covers all possible examples because trivial hypothesis
return None
else:
head_predicate = clause.get_head().get_predicate()
head_args = clause.get_head_arguments()
# print("{}({})".format(head_predicate, *head_args))
sols = self._solver.query(*clause.get_body().get_literals())
self._prolog_queries += 1 if count_as_query else 0
# Build a solution by substituting Variables with their found value
# and copying constants without change
sols = [head_predicate(*[s[v] if isinstance(v,Variable) else v for v in head_args]) for s in sols]
return sols
def compute_bottom_clause(theory: Sequence[Clause], c: Clause) -> Clause:
"""
Computes the bottom clause given a theory and a clause.
Algorithm from (De Raedt,2008)
"""
# 1. Find a skolemization substitution θ for c (w.r.t. B and c)
_, theta = skolemize(c)
# 2. Compute the least Herbrand model M of theory ¬body(c)θ
body_facts = [
Clause(l.substitute(theta), []) for l in c.get_body().get_literals()
]
m = herbrand_model(theory + body_facts)
# 3. Deskolemize the clause head(cθ) <= M and return the result.
theta_inv = {value: key for key, value in theta.items()}
return Clause(c.get_head(),
[l.get_head().substitute(theta_inv) for l in m])
