Drop processing of literals with LiteralProxies class

[wrobell]

This is possible, because RDFLib supports literals in subject position now (see discussion in issue #13).

As a consequence

1. The change improves performance of the library, for the script below, by
   about 14%.

2. Related blocks of code, which swallow exceptions are removed.

3. Unit tests for the following OWL 2 RL rules are implemented

   • cax-dw
   • cls-avf
   • cls-maxc1
   • cls-maxc2
   • cls-maxqc1
   • cls-maxqc2
   • cls-maxqc3
   • cls-maxqc4

4. Unit tests for RDFS closure implemented

   • adding datatype axioms
   • one time rules

5. Unit tests for OWL 2 RL extras closure implemented

   • one time rules

Testing script

import io
import sys
import time
import owlrl
from rdflib import Graph, Namespace, BNode, Literal, XSD

T = Namespace('http://test.net/')

DATA = """
@prefix xsd: <http://www.w3.org/2001/XMLSchema#>.
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix owl: <http://www.w3.org/2002/07/owl#>.
@prefix : <http://test.net/>.

:C a owl:Class.
:dprop a owl:DatatypeProperty;
    rdfs:domain :C;
    rdfs:range xsd:integer.
""" 

test_name = sys.argv[1]

dprop = T.dprop
print('test,graph_size,time')
for _ in range(10):

    g = Graph()
    g.parse(io.StringIO(DATA), format='n3')

    for i in range(10):
        d = BNode()
        for j in range(200):
            b = BNode()
            g.add((b, dprop, Literal(j * 10, datatype=XSD.integer)))

    t = time.time()
    owlrl.DeductiveClosure(owlrl.OWLRL_Semantics).expand(g)
    duration = time.time() - t
    print('{},{},{:.6f}'.format(test_name, len(g), duration))

[ashleysommer]

@wrobell are you done pushing commits to this PR? Let us know when it is ready for review.

[wrobell]

Hi, sorry, I have raised this pull request too early. I will have few more fixes. I will comment once its done.

[ashleysommer]

@wrobell we've noticed no new commit to this branch since November 7.
Is this ready to review and merge?

[wrobell]

Unfortunately, this still needs work. I hope to have some time to work on it today.

[wrobell]

This pull request is ready. Please review.