diff --git a/spec/integration/axiom/algebra/difference/optimize_spec.rb b/spec/integration/axiom/algebra/difference/optimize_spec.rb
index 1c06cb6..89c231e 100644
--- a/spec/integration/axiom/algebra/difference/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/difference/optimize_spec.rb
@@ -19,8 +19,8 @@
   end
 
   context 'left is an empty relation' do
-    let(:left)  { Relation::Empty.new(header) }
-    let(:right) { original_right              }
+    let(:left)  { Relation.new(header) }
+    let(:right) { original_right       }
 
     it { should be(left) }
 
@@ -37,8 +37,8 @@
   end
 
   context 'right is an empty relation' do
-    let(:left)  { original_left               }
-    let(:right) { Relation::Empty.new(header) }
+    let(:left)  { original_left        }
+    let(:right) { Relation.new(header) }
 
     it { should be(left) }
 
@@ -58,7 +58,7 @@
     let(:left)  { Algebra::Restriction.new(original_left, Function::Proposition::Contradiction.instance) }
     let(:right) { original_right                                                                         }
 
-    it { should eql(Relation::Empty.new(left.header | right.header)) }
+    it { should eql(Relation.new(left.header | right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -106,7 +106,7 @@
       let(:left)       { original_left             }
       let(:right)      { original_right            }
 
-      it { should eql(Relation::Empty.new(header)) }
+      it { should eql(Relation.new(header)) }
 
       it 'returns an equivalent relation to the unoptimized operation' do
         should == object
diff --git a/spec/integration/axiom/algebra/intersection/optimize_spec.rb b/spec/integration/axiom/algebra/intersection/optimize_spec.rb
index 5984add..ef99fd8 100644
--- a/spec/integration/axiom/algebra/intersection/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/intersection/optimize_spec.rb
@@ -19,8 +19,8 @@
   end
 
   context 'left is an empty relation' do
-    let(:left)  { Relation::Empty.new(header) }
-    let(:right) { original_right              }
+    let(:left)  { Relation.new(header) }
+    let(:right) { original_right       }
 
     it { should be(left) }
 
@@ -37,8 +37,8 @@
   end
 
   context 'right is an empty relation' do
-    let(:left)  { original_left               }
-    let(:right) { Relation::Empty.new(header) }
+    let(:left)  { original_left        }
+    let(:right) { Relation.new(header) }
 
     it { should be(right) }
 
@@ -58,7 +58,7 @@
     let(:left)  { Algebra::Restriction.new(original_left, Function::Proposition::Contradiction.instance) }
     let(:right) { original_right                                                                         }
 
-    it { should eql(Relation::Empty.new(left.header | right.header)) }
+    it { should eql(Relation.new(left.header | right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -81,7 +81,7 @@
     let(:left)  { original_left                                                                           }
     let(:right) { Algebra::Restriction.new(original_right, Function::Proposition::Contradiction.instance) }
 
-    it { should eql(Relation::Empty.new(left.header | right.header)) }
+    it { should eql(Relation.new(left.header | right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/join/optimize_spec.rb b/spec/integration/axiom/algebra/join/optimize_spec.rb
index fe0b4b7..beda0e6 100644
--- a/spec/integration/axiom/algebra/join/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/join/optimize_spec.rb
@@ -14,9 +14,9 @@
   let(:object)         { described_class.new(left, right)                            }
 
   context 'left is an empty relation' do
-    let(:left) { Relation::Empty.new(original_left.header) }
+    let(:left) { Relation.new(original_left.header) }
 
-    it { should eql(Relation::Empty.new(right.header)) }
+    it { should eql(Relation.new(right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -31,9 +31,9 @@
   end
 
   context 'right is an empty relation' do
-    let(:right) { Relation::Empty.new(original_right.header) }
+    let(:right) { Relation.new(original_right.header) }
 
-    it { should eql(Relation::Empty.new(right.header)) }
+    it { should eql(Relation.new(right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -50,7 +50,7 @@
   context 'left is an empty relation when optimized' do
     let(:left) { Algebra::Restriction.new(original_left, Function::Proposition::Contradiction.instance) }
 
-    it { should eql(Relation::Empty.new(right.header)) }
+    it { should eql(Relation.new(right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -67,7 +67,7 @@
   context 'right is an empty relation when optimized' do
     let(:right) { Algebra::Restriction.new(original_right, Function::Proposition::Contradiction.instance) }
 
-    it { should eql(Relation::Empty.new(right.header)) }
+    it { should eql(Relation.new(right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/product/optimize_spec.rb b/spec/integration/axiom/algebra/product/optimize_spec.rb
index 4d0733d..2e4115b 100644
--- a/spec/integration/axiom/algebra/product/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/product/optimize_spec.rb
@@ -14,7 +14,7 @@
   context 'left is a TABLE_DUM' do
     let(:left) { TABLE_DUM }
 
-    it { should eql(Relation::Empty.new(right.header)) }
+    it { should eql(Relation.new(right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -31,7 +31,7 @@
   context 'right is a TABLE_DUM' do
     let(:right) { TABLE_DUM }
 
-    it { should eql(Relation::Empty.new(left.header)) }
+    it { should eql(Relation.new(left.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -48,7 +48,7 @@
   context 'left is a TABLE_DUM when optimized' do
     let(:left) { TABLE_DUM.project([]) }
 
-    it { should eql(Relation::Empty.new(right.header)) }
+    it { should eql(Relation.new(right.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -65,7 +65,7 @@
   context 'right is a TABLE_DUM when optimized' do
     let(:right) { TABLE_DUM.project([]) }
 
-    it { should eql(Relation::Empty.new(left.header)) }
+    it { should eql(Relation.new(left.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/projection/optimize_spec.rb b/spec/integration/axiom/algebra/projection/optimize_spec.rb
index da80a8d..35c9a8a 100644
--- a/spec/integration/axiom/algebra/projection/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/projection/optimize_spec.rb
@@ -62,10 +62,10 @@
   end
 
   context 'containing an empty relation' do
-    let(:operand)    { Relation::Empty.new(header) }
-    let(:attributes) { [:id]                       }
+    let(:operand)    { Relation.new(header) }
+    let(:attributes) { [:id]                }
 
-    it { should eql(Relation::Empty.new(object.header)) }
+    it { should eql(Relation.new(object.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -78,7 +78,7 @@
     let(:operand)    { Algebra::Restriction.new(relation, Function::Proposition::Contradiction.instance) }
     let(:attributes) { [:id]                                                                             }
 
-    it { should eql(Relation::Empty.new(object.header)) }
+    it { should eql(Relation.new(object.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/rename/optimize_spec.rb b/spec/integration/axiom/algebra/rename/optimize_spec.rb
index f74cb21..332151e 100644
--- a/spec/integration/axiom/algebra/rename/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/rename/optimize_spec.rb
@@ -23,9 +23,9 @@
   end
 
   context 'containing an empty relation' do
-    let(:operand) { Relation::Empty.new(relation.header) }
+    let(:operand) { Relation.new(relation.header) }
 
-    it { should eql(Relation::Empty.new(object.header)) }
+    it { should eql(Relation.new(object.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/restriction/optimize_spec.rb b/spec/integration/axiom/algebra/restriction/optimize_spec.rb
index 442bf02..a31a28c 100644
--- a/spec/integration/axiom/algebra/restriction/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/restriction/optimize_spec.rb
@@ -25,7 +25,7 @@
   context 'with a contradiction' do
     let(:predicate) { Function::Proposition::Contradiction.instance }
 
-    it { should eql(Relation::Empty.new(relation.header)) }
+    it { should eql(Relation.new(relation.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
@@ -121,7 +121,7 @@
     let(:operand)   { described_class.new(relation, Function::Proposition::Contradiction.instance) }
     let(:predicate) { operand[:id].gte(1)                                                          }
 
-    it { should eql(Relation::Empty.new(relation.header)) }
+    it { should eql(Relation.new(relation.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/summarization/optimize_spec.rb b/spec/integration/axiom/algebra/summarization/optimize_spec.rb
index 2e4205e..21feb79 100644
--- a/spec/integration/axiom/algebra/summarization/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/summarization/optimize_spec.rb
@@ -33,7 +33,7 @@
   context 'when the summarize_per is empty' do
     let(:summarize_per) { relation.project([:id]).restrict { false } }
 
-    it { should eql(Relation::Empty.new(object.header)) }
+    it { should eql(Relation.new(object.header)) }
 
     it 'returns an equivalent relation to the unoptimized operation' do
       should == object
diff --git a/spec/integration/axiom/algebra/union/optimize_spec.rb b/spec/integration/axiom/algebra/union/optimize_spec.rb
index f1acfb8..a42a490 100644
--- a/spec/integration/axiom/algebra/union/optimize_spec.rb
+++ b/spec/integration/axiom/algebra/union/optimize_spec.rb
@@ -19,8 +19,8 @@
   end
 
   context 'left is an empty relation' do
-    let(:left)  { Relation::Empty.new(header) }
-    let(:right) { original_right              }
+    let(:left)  { Relation.new(header) }
+    let(:right) { original_right       }
 
     it { should be(right) }
 
@@ -42,8 +42,8 @@
   end
 
   context 'right is an empty relation' do
-    let(:left)  { original_left               }
-    let(:right) { Relation::Empty.new(header) }
+    let(:left)  { original_left        }
+    let(:right) { Relation.new(header) }
 
     it { should be(left) }
 
diff --git a/spec/integration/axiom/relation/materialized/optimize_spec.rb b/spec/integration/axiom/relation/materialized/optimize_spec.rb
index a1e1913..a287942 100644
--- a/spec/integration/axiom/relation/materialized/optimize_spec.rb
+++ b/spec/integration/axiom/relation/materialized/optimize_spec.rb
@@ -10,7 +10,7 @@
   context 'with an empty Array' do
     let(:body) { [] }
 
-    it { should eql(Relation::Empty.new(object.header)) }
+    it { should eql(Relation.new(object.header)) }
 
     it 'returns an equivalent object to the unoptimized operation' do
       should == object
diff --git a/spec/unit/axiom/optimizer/algebra/difference/empty_left/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/difference/empty_left/optimize_spec.rb
index 9c86566..6d49951 100644
--- a/spec/unit/axiom/optimizer/algebra/difference/empty_left/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/difference/empty_left/optimize_spec.rb
@@ -6,7 +6,7 @@
   subject { object.optimize }
 
   let(:header)   { Relation::Header.coerce([[:id, Integer]])       }
-  let(:left)     { Relation::Empty.new(header)                     }
+  let(:left)     { Relation.new(header)                            }
   let(:right)    { Relation.new(header, LazyEnumerable.new([[1]])) }
   let(:relation) { left.difference(right)                          }
   let(:object)   { described_class.new(relation)                   }
diff --git a/spec/unit/axiom/optimizer/algebra/difference/empty_right/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/difference/empty_right/optimize_spec.rb
index 8db9dc5..892e5c3 100644
--- a/spec/unit/axiom/optimizer/algebra/difference/empty_right/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/difference/empty_right/optimize_spec.rb
@@ -7,7 +7,7 @@
 
   let(:header)   { Relation::Header.coerce([[:id, Integer]])       }
   let(:left)     { Relation.new(header, LazyEnumerable.new([[1]])) }
-  let(:right)    { Relation::Empty.new(header)                     }
+  let(:right)    { Relation.new(header)                            }
   let(:relation) { left.difference(right)                          }
   let(:object)   { described_class.new(relation)                   }
 
diff --git a/spec/unit/axiom/optimizer/algebra/intersection/empty_left/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/intersection/empty_left/optimize_spec.rb
index 61dbd94..5483f51 100644
--- a/spec/unit/axiom/optimizer/algebra/intersection/empty_left/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/intersection/empty_left/optimize_spec.rb
@@ -6,7 +6,7 @@
   subject { object.optimize }
 
   let(:header)   { Relation::Header.coerce([[:id, Integer]])       }
-  let(:left)     { Relation::Empty.new(header)                     }
+  let(:left)     { Relation.new(header)                            }
   let(:right)    { Relation.new(header, LazyEnumerable.new([[1]])) }
   let(:relation) { left.intersect(right)                           }
   let(:object)   { described_class.new(relation)                   }
diff --git a/spec/unit/axiom/optimizer/algebra/intersection/empty_right/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/intersection/empty_right/optimize_spec.rb
index 8088144..9e93a72 100644
--- a/spec/unit/axiom/optimizer/algebra/intersection/empty_right/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/intersection/empty_right/optimize_spec.rb
@@ -7,7 +7,7 @@
 
   let(:header)   { Relation::Header.coerce([[:id, Integer]])       }
   let(:left)     { Relation.new(header, LazyEnumerable.new([[1]])) }
-  let(:right)    { Relation::Empty.new(header)                     }
+  let(:right)    { Relation.new(header)                            }
   let(:relation) { left.intersect(right)                           }
   let(:object)   { described_class.new(relation)                   }
 
diff --git a/spec/unit/axiom/optimizer/algebra/join/materialized_left/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/join/materialized_left/optimize_spec.rb
index ccdd836..c780e4c 100644
--- a/spec/unit/axiom/optimizer/algebra/join/materialized_left/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/join/materialized_left/optimize_spec.rb
@@ -18,7 +18,7 @@
 
     it { should be_kind_of(Algebra::Join) }
 
-    its(:left) { should eql(Relation::Empty.new(left.header)) }
+    its(:left) { should eql(Relation.new(left.header)) }
 
     its(:right) { should eql(right.restrict { Function::Proposition::Contradiction.instance }) }
   end
diff --git a/spec/unit/axiom/optimizer/algebra/join/materialized_right/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/join/materialized_right/optimize_spec.rb
index 99b0e9d..bdb6e50 100644
--- a/spec/unit/axiom/optimizer/algebra/join/materialized_right/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/join/materialized_right/optimize_spec.rb
@@ -20,7 +20,7 @@
 
     its(:left) { should eql(left.restrict { Function::Proposition::Contradiction.instance }) }
 
-    its(:right) { should eql(Relation::Empty.new(right.header)) }
+    its(:right) { should eql(Relation.new(right.header)) }
   end
 
   context 'with one joined tuple' do
diff --git a/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimizable_predicate_spec.rb b/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimizable_predicate_spec.rb
index b592ac3..7fc2590 100644
--- a/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimizable_predicate_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimizable_predicate_spec.rb
@@ -14,7 +14,7 @@
   end
 
   context 'when the operand is empty' do
-    let(:operand) { Relation::Empty.new(header) }
+    let(:operand) { Relation.new(header) }
 
     it { should be(true) }
   end
diff --git a/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimize_spec.rb
index 32dc8b6..6d8dca9 100644
--- a/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/projection/empty_operand/optimize_spec.rb
@@ -6,7 +6,7 @@
   subject { object.optimize }
 
   let(:header)   { Relation::Header.coerce([[:id, Integer], [:name, String]]) }
-  let(:base)     { Relation::Empty.new(header)                                }
+  let(:base)     { Relation.new(header)                                       }
   let(:relation) { base.project([:id])                                        }
   let(:object)   { described_class.new(relation)                              }
 
diff --git a/spec/unit/axiom/optimizer/algebra/rename/empty_operand/optimizable_predicate_spec.rb b/spec/unit/axiom/optimizer/algebra/rename/empty_operand/optimizable_predicate_spec.rb
index 09ea60c..8367662 100644
--- a/spec/unit/axiom/optimizer/algebra/rename/empty_operand/optimizable_predicate_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/rename/empty_operand/optimizable_predicate_spec.rb
@@ -14,7 +14,7 @@
   end
 
   context 'when the operand is an empty relation' do
-    let(:operand) { Relation::Empty.new(header) }
+    let(:operand) { Relation.new(header) }
 
     it { should be(true) }
   end
diff --git a/spec/unit/axiom/optimizer/algebra/union/empty_left/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/union/empty_left/optimize_spec.rb
index db5cfa2..8caffee 100644
--- a/spec/unit/axiom/optimizer/algebra/union/empty_left/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/union/empty_left/optimize_spec.rb
@@ -6,7 +6,7 @@
   subject { object.optimize }
 
   let(:header)   { Relation::Header.coerce([[:id, Integer]])       }
-  let(:left)     { Relation::Empty.new(header)                     }
+  let(:left)     { Relation.new(header)                            }
   let(:right)    { Relation.new(header, LazyEnumerable.new([[2]])) }
   let(:relation) { left.union(right)                               }
   let(:object)   { described_class.new(relation)                   }
diff --git a/spec/unit/axiom/optimizer/algebra/union/empty_right/optimize_spec.rb b/spec/unit/axiom/optimizer/algebra/union/empty_right/optimize_spec.rb
index 8305844..fccb248 100644
--- a/spec/unit/axiom/optimizer/algebra/union/empty_right/optimize_spec.rb
+++ b/spec/unit/axiom/optimizer/algebra/union/empty_right/optimize_spec.rb
@@ -7,7 +7,7 @@
 
   let(:header)   { Relation::Header.coerce([[:id, Integer]])       }
   let(:left)     { Relation.new(header, LazyEnumerable.new([[1]])) }
-  let(:right)    { Relation::Empty.new(header)                     }
+  let(:right)    { Relation.new(header)                            }
   let(:relation) { left.union(right)                               }
   let(:object)   { described_class.new(relation)                   }