Shortest-path ASP Theoretic

Getting started

The framework is released as EGG file to be used on a Desktop platform, therefore it can be easily installed in a Theoretic installation.

The framework needs ANTLR4 library for its operation.

Using EmbASP

In the following, we describe an actual usage of the framework by means of a running example; as a use case, we will develop a simple Desktop application to solve the shortest-path problem.

The complete code of this example is freely available here.

We will make use of the annotation-guided mapping, in order to create Theoretic object constituting ASP predicates.

To this purpose, the following classes are intended to represent possible predicates that an ASP program can use:

class Edge(Predicate):
  predicate_name = "edge"

  def __init__(self, source=None, destination=None, weight=None):
    Predicate.__init__(self, [("source"),("destination"),("weight")])
    self.source = source
    self.destination = destination
    self.weight = weight

  [...]

class Path(Predicate):
  predicate_name = "path"

  def __init__(self, source=None, destination=None, weight=None):
    Predicate.__init__(self, [("source"),("destination"),("weight")])
    self.source = source
    self.destination = destination
    self.weight = weight

  [...]

At this point, supposing that we have embedded the DLV2 solver in this project, we can start deploying our application:

def getEdges():

  edges = []

  edges.append(Edge(0,1,1))
  edges.append(Edge(0,2,4))
  edges.append(Edge(1,2,2))
  edges.append(Edge(1,3,4))
  edges.append(Edge(1,4,1))
  edges.append(Edge(2,4,4))
  edges.append(Edge(3,5,6))
  edges.append(Edge(3,6,1))
  edges.append(Edge(4,3,1))
  edges.append(Edge(6,4,5))
  edges.append(Edge(6,5,9))
  edges.append(Edge(6,7,1))
  edges.append(Edge(7,5,2))

  return edges

try:

  handler = DesktopHandler(DLV2DesktopService("../../executable/dlv2"))

  ASPMapper.get_instance().register_class(Edge)
  ASPMapper.get_instance().register_class(Path)

  inputProgram = ASPInputProgram()

  source = 0    # source node
  destination = 7    # destination node

  rules = "source(" + str(self.source) + "). destination(" + str(self.destination) + ")."
  rules += "path(X,Y,W) | notPath(X,Y,W) :- source(X), edge(X,Y,W)."
  rules += "path(X,Y,W) | notPath(X,Y,W) :- path(_,X,_), edge(X,Y,W), not to(X)."
  rules += "visited(X) :- path(_,X,_)."
  rules += ":- destination(X), not visited(X)."
  rules += ":~ path(X,Y,W). [W@1 ,X,Y]"

  inputProgram.add_program(rules)
  inputProgram.add_objects_input(self.getEdges())

  handler.add_program(inputProgram)

  answerSets = handler.start_sync()

  for answerSet in answerSets.get_optimal_answer_sets():
      path = []     # edges in the shortest path (unsorted)
      sum_ = 0      # total weight of the path

      for obj in answerSet.get_atoms():
          if isinstance(obj, Path):
              path.append(obj)
              sum_ += int(obj.get_weight())

      sortedPath = []   # edges in the shortest path (sorted)
      join(source, path, sortedPath)   # sorts the edges
      show(sortedPath, sum_)     # shows the path

except Exception as e:
  print(str(e))

The class contains an Handler instance as field, that is initialized with a DesktopHandler using the parameter DLV2DesktopService with a string representing the path to the DLV2 local solver.

The ASPMapper registers the classes created before in order to manage the input and output objects.

A string and a list of Edge representing facts, rules and constraints of the ASP program are added to an ASPInputProgram, and the ASPInputProgram is added to the Handler.

Finally the solver is invoked, and the output is retrieved.

The output predicates can be managed accordingly to the user’s desiderata. In this example the Path predicates, that represent the shortest path, are collected, sorted, and printed as well as the total weight of the path.

For further information, contact embasp@mat.unical.it or visit our website.