diff --git a/graph/iterator.go b/graph/iterator.go
index ec680b8..6d91d86 100644
--- a/graph/iterator.go
+++ b/graph/iterator.go
@@ -19,6 +19,7 @@ package graph
 
 import (
 	"strings"
+	"sync"
 
 	"github.com/barakmich/glog"
 )
@@ -96,7 +97,7 @@ type Iterator interface {
 
 	// Returns a string relating to what the function of the iterator is. By
 	// knowing the names of the iterators, we can devise optimization strategies.
-	Type() string
+	Type() Type
 
 	// Optimizes an iterator. Can replace the iterator, or merely move things
 	// around internally. if it chooses to replace it with a better iterator,
@@ -126,20 +127,73 @@ type IteratorStats struct {
 	Size      int64
 }
 
+type Type int
+
+const (
+	Invalid Type = iota
+	All
+	And
+	Or
+	HasA
+	LinksTo
+	Comparison
+	Null
+	Fixed
+	Not
+	Optional
+)
+
+var (
+	lock sync.Mutex
+	// These strings must be kept in order consistent with the Type const block above.
+	types = []string{
+		"invalid",
+		"all",
+		"and",
+		"or",
+		"hasa",
+		"linksto",
+		"comparison",
+		"null",
+		"fixed",
+		"not",
+		"optional",
+	}
+)
+
+func Register(name string) Type {
+	lock.Lock()
+	defer lock.Unlock()
+	for i, t := range types {
+		if t == name {
+			return Type(i)
+		}
+	}
+	types = append(types, name)
+	return Type(len(types) - 1)
+}
+
+func (t Type) String() string {
+	if t < 0 || int(t) >= len(types) {
+		return "illegal-type"
+	}
+	return types[t]
+}
+
 // Utility logging functions for when an iterator gets called Next upon, or Check upon, as
 // well as what they return. Highly useful for tracing the execution path of a query.
 func CheckLogIn(it Iterator, val Value) {
 	if glog.V(4) {
-		glog.V(4).Infof("%s %d CHECK %d", strings.ToUpper(it.Type()), it.UID(), val)
+		glog.V(4).Infof("%s %d CHECK %d", strings.ToUpper(it.Type().String()), it.UID(), val)
 	}
 }
 
 func CheckLogOut(it Iterator, val Value, good bool) bool {
 	if glog.V(4) {
 		if good {
-			glog.V(4).Infof("%s %d CHECK %d GOOD", strings.ToUpper(it.Type()), it.UID(), val)
+			glog.V(4).Infof("%s %d CHECK %d GOOD", strings.ToUpper(it.Type().String()), it.UID(), val)
 		} else {
-			glog.V(4).Infof("%s %d CHECK %d BAD", strings.ToUpper(it.Type()), it.UID(), val)
+			glog.V(4).Infof("%s %d CHECK %d BAD", strings.ToUpper(it.Type().String()), it.UID(), val)
 		}
 	}
 	return good
@@ -147,16 +201,16 @@ func CheckLogOut(it Iterator, val Value, good bool) bool {
 
 func NextLogIn(it Iterator) {
 	if glog.V(4) {
-		glog.V(4).Infof("%s %d NEXT", strings.ToUpper(it.Type()), it.UID())
+		glog.V(4).Infof("%s %d NEXT", strings.ToUpper(it.Type().String()), it.UID())
 	}
 }
 
 func NextLogOut(it Iterator, val Value, ok bool) (Value, bool) {
 	if glog.V(4) {
 		if ok {
-			glog.V(4).Infof("%s %d NEXT IS %d", strings.ToUpper(it.Type()), it.UID(), val)
+			glog.V(4).Infof("%s %d NEXT IS %d", strings.ToUpper(it.Type().String()), it.UID(), val)
 		} else {
-			glog.V(4).Infof("%s %d NEXT DONE", strings.ToUpper(it.Type()), it.UID())
+			glog.V(4).Infof("%s %d NEXT DONE", strings.ToUpper(it.Type().String()), it.UID())
 		}
 	}
 	return val, ok
diff --git a/graph/iterator/all_iterator.go b/graph/iterator/all_iterator.go
index 4cd6aa1..52b5cf7 100644
--- a/graph/iterator/all_iterator.go
+++ b/graph/iterator/all_iterator.go
@@ -101,7 +101,7 @@ func (it *Int64) Check(tsv graph.Value) bool {
 
 // The type of this iterator is an "all". This is important, as it puts it in
 // the class of "all iterators.
-func (it *Int64) Type() string { return "all" }
+func (it *Int64) Type() graph.Type { return graph.All }
 
 // There's nothing to optimize about this little iterator.
 func (it *Int64) Optimize() (graph.Iterator, bool) { return it, false }
diff --git a/graph/iterator/and_iterator.go b/graph/iterator/and_iterator.go
index 66a51cf..819cb42 100644
--- a/graph/iterator/and_iterator.go
+++ b/graph/iterator/and_iterator.go
@@ -246,4 +246,4 @@ func (it *And) Close() {
 }
 
 // Register this as an "and" iterator.
-func (it *And) Type() string { return "and" }
+func (it *And) Type() graph.Type { return graph.And }
diff --git a/graph/iterator/and_iterator_optimize.go b/graph/iterator/and_iterator_optimize.go
index e0e7503..b556094 100644
--- a/graph/iterator/and_iterator_optimize.go
+++ b/graph/iterator/and_iterator_optimize.go
@@ -134,7 +134,7 @@ func (_ *And) optimizeReplacement(its []graph.Iterator) graph.Iterator {
 func optimizeOrder(its []graph.Iterator) []graph.Iterator {
 	var (
 		// bad contains iterators that can't be (efficiently) nexted, such as
-		// "optional" or "not". Separate them out and tack them on at the end.
+		// graph.Optional or graph.Not. Separate them out and tack them on at the end.
 		out, bad []graph.Iterator
 		best     graph.Iterator
 		bestCost = int64(1 << 62)
@@ -257,25 +257,25 @@ func optimizeSubIterators(its []graph.Iterator) []graph.Iterator {
 // Check a list of iterators for any Null iterators.
 func hasAnyNullIterators(its []graph.Iterator) bool {
 	for _, it := range its {
-		if it.Type() == "null" {
+		if it.Type() == graph.Null {
 			return true
 		}
 	}
 	return false
 }
 
-// There are two "not-useful" iterators -- namely "null" which returns
-// nothing, and "all" which returns everything. Particularly, we want
-// to see if we're intersecting with a bunch of "all" iterators, and,
+// There are two "not-useful" iterators -- namely graph.Null which returns
+// nothing, and graph.All which returns everything. Particularly, we want
+// to see if we're intersecting with a bunch of graph.All iterators, and,
 // if we are, then we have only one useful iterator.
 func hasOneUsefulIterator(its []graph.Iterator) graph.Iterator {
 	usefulCount := 0
 	var usefulIt graph.Iterator
 	for _, it := range its {
 		switch it.Type() {
-		case "null", "all":
+		case graph.Null, graph.All:
 			continue
-		case "optional":
+		case graph.Optional:
 			// Optional is weird -- it's not useful, but we can't optimize
 			// away from it. Therefore, we skip this optimization
 			// if we see one.
diff --git a/graph/iterator/and_iterator_optimize_test.go b/graph/iterator/and_iterator_optimize_test.go
index 846f781..e8d6a80 100644
--- a/graph/iterator/and_iterator_optimize_test.go
+++ b/graph/iterator/and_iterator_optimize_test.go
@@ -21,6 +21,8 @@ import (
 	"reflect"
 	"sort"
 	"testing"
+
+	"github.com/google/cayley/graph"
 )
 
 func TestIteratorPromotion(t *testing.T) {
@@ -37,7 +39,7 @@ func TestIteratorPromotion(t *testing.T) {
 	if !changed {
 		t.Error("Iterator didn't optimize")
 	}
-	if newIt.Type() != "fixed" {
+	if newIt.Type() != graph.Fixed {
 		t.Error("Expected fixed iterator")
 	}
 	tagsExpected := []string{"a", "b", "c"}
@@ -58,7 +60,7 @@ func TestNullIteratorAnd(t *testing.T) {
 	if !changed {
 		t.Error("Didn't change")
 	}
-	if newIt.Type() != "null" {
+	if newIt.Type() != graph.Null {
 		t.Error("Expected null iterator, got ", newIt.Type())
 	}
 }
diff --git a/graph/iterator/fixed_iterator.go b/graph/iterator/fixed_iterator.go
index 8eca523..c69869b 100644
--- a/graph/iterator/fixed_iterator.go
+++ b/graph/iterator/fixed_iterator.go
@@ -99,9 +99,7 @@ func (it *Fixed) DebugString(indent int) string {
 }
 
 // Register this iterator as a Fixed iterator.
-func (it *Fixed) Type() string {
-	return "fixed"
-}
+func (it *Fixed) Type() graph.Type { return graph.Fixed }
 
 // Check if the passed value is equal to one of the values stored in the iterator.
 func (it *Fixed) Check(v graph.Value) bool {
diff --git a/graph/iterator/hasa_iterator.go b/graph/iterator/hasa_iterator.go
index c253923..b434288 100644
--- a/graph/iterator/hasa_iterator.go
+++ b/graph/iterator/hasa_iterator.go
@@ -91,7 +91,7 @@ func (it *HasA) Optimize() (graph.Iterator, bool) {
 	newPrimary, changed := it.primaryIt.Optimize()
 	if changed {
 		it.primaryIt = newPrimary
-		if it.primaryIt.Type() == "null" {
+		if it.primaryIt.Type() == graph.Null {
 			return it.primaryIt, true
 		}
 	}
@@ -220,4 +220,4 @@ func (it *HasA) Close() {
 }
 
 // Register this iterator as a HasA.
-func (it *HasA) Type() string { return "hasa" }
+func (it *HasA) Type() graph.Type { return graph.HasA }
diff --git a/graph/iterator/iterator.go b/graph/iterator/iterator.go
index 8658137..e2029d5 100644
--- a/graph/iterator/iterator.go
+++ b/graph/iterator/iterator.go
@@ -174,7 +174,7 @@ func NewNull() *Null {
 func (it *Null) Clone() graph.Iterator { return NewNull() }
 
 // Name the null iterator.
-func (it *Null) Type() string { return "null" }
+func (it *Null) Type() graph.Type { return graph.Null }
 
 // A good iterator will close itself when it returns true.
 // Null has nothing it needs to do.
diff --git a/graph/iterator/linksto_iterator.go b/graph/iterator/linksto_iterator.go
index 27d496e..8488954 100644
--- a/graph/iterator/linksto_iterator.go
+++ b/graph/iterator/linksto_iterator.go
@@ -118,7 +118,7 @@ func (it *LinksTo) Optimize() (graph.Iterator, bool) {
 	newPrimary, changed := it.primaryIt.Optimize()
 	if changed {
 		it.primaryIt = newPrimary
-		if it.primaryIt.Type() == "null" {
+		if it.primaryIt.Type() == graph.Null {
 			it.nextIt.Close()
 			return it.primaryIt, true
 		}
@@ -166,7 +166,7 @@ func (it *LinksTo) NextResult() bool {
 }
 
 // Register the LinksTo.
-func (it *LinksTo) Type() string { return "linksto" }
+func (it *LinksTo) Type() graph.Type { return graph.LinksTo }
 
 // Return a guess as to how big or costly it is to next the iterator.
 func (it *LinksTo) Stats() graph.IteratorStats {
diff --git a/graph/iterator/optional_iterator.go b/graph/iterator/optional_iterator.go
index f69959b..46c6dd6 100644
--- a/graph/iterator/optional_iterator.go
+++ b/graph/iterator/optional_iterator.go
@@ -104,7 +104,7 @@ func (it *Optional) TagResults(dst map[string]graph.Value) {
 }
 
 // Registers the optional iterator.
-func (it *Optional) Type() string { return "optional" }
+func (it *Optional) Type() graph.Type { return graph.Optional }
 
 // Prints the optional and it's subiterator.
 func (it *Optional) DebugString(indent int) string {
diff --git a/graph/iterator/or_iterator.go b/graph/iterator/or_iterator.go
index 6b98185..0bc5023 100644
--- a/graph/iterator/or_iterator.go
+++ b/graph/iterator/or_iterator.go
@@ -281,4 +281,4 @@ func (it *Or) Stats() graph.IteratorStats {
 }
 
 // Register this as an "or" graph.iterator.
-func (it *Or) Type() string { return "or" }
+func (it *Or) Type() graph.Type { return graph.Or }
diff --git a/graph/iterator/query_shape.go b/graph/iterator/query_shape.go
index 7e34d77..da40db9 100644
--- a/graph/iterator/query_shape.go
+++ b/graph/iterator/query_shape.go
@@ -115,18 +115,18 @@ func (qs *queryShape) MakeNode(it graph.Iterator) *Node {
 	}
 
 	switch it.Type() {
-	case "and":
+	case graph.And:
 		for _, sub := range it.SubIterators() {
 			qs.nodeId++
 			newNode := qs.MakeNode(sub)
-			if sub.Type() != "or" {
+			if sub.Type() != graph.Or {
 				qs.StealNode(&n, newNode)
 			} else {
 				qs.AddNode(newNode)
 				qs.AddLink(&Link{n.Id, newNode.Id, 0, 0})
 			}
 		}
-	case "fixed":
+	case graph.Fixed:
 		n.IsFixed = true
 		for {
 			val, more := it.Next()
@@ -135,25 +135,25 @@ func (qs *queryShape) MakeNode(it graph.Iterator) *Node {
 			}
 			n.Values = append(n.Values, qs.ts.NameOf(val))
 		}
-	case "hasa":
+	case graph.HasA:
 		hasa := it.(*HasA)
 		qs.PushHasa(n.Id, hasa.dir)
 		qs.nodeId++
 		newNode := qs.MakeNode(hasa.primaryIt)
 		qs.AddNode(newNode)
 		qs.RemoveHasa()
-	case "or":
+	case graph.Or:
 		for _, sub := range it.SubIterators() {
 			qs.nodeId++
 			newNode := qs.MakeNode(sub)
-			if sub.Type() == "or" {
+			if sub.Type() == graph.Or {
 				qs.StealNode(&n, newNode)
 			} else {
 				qs.AddNode(newNode)
 				qs.AddLink(&Link{n.Id, newNode.Id, 0, 0})
 			}
 		}
-	case "linksto":
+	case graph.LinksTo:
 		n.IsLinkNode = true
 		lto := it.(*LinksTo)
 		qs.nodeId++
@@ -167,15 +167,15 @@ func (qs *queryShape) MakeNode(it graph.Iterator) *Node {
 			} else {
 				qs.AddLink(&Link{newNode.Id, hasaID, 0, n.Id})
 			}
-		} else if lto.primaryIt.Type() == "fixed" {
+		} else if lto.primaryIt.Type() == graph.Fixed {
 			qs.StealNode(&n, newNode)
 		} else {
 			qs.AddNode(newNode)
 		}
-	case "optional":
+	case graph.Optional:
 		// Unsupported, for the moment
 		fallthrough
-	case "all":
+	case graph.All:
 	}
 	return &n
 }
diff --git a/graph/iterator/value_comparison_iterator.go b/graph/iterator/value_comparison_iterator.go
index 8c36795..611d549 100644
--- a/graph/iterator/value_comparison_iterator.go
+++ b/graph/iterator/value_comparison_iterator.go
@@ -162,7 +162,7 @@ func (it *Comparison) TagResults(dst map[string]graph.Value) {
 }
 
 // Registers the value-comparison iterator.
-func (it *Comparison) Type() string { return "value-comparison" }
+func (it *Comparison) Type() graph.Type { return graph.Comparison }
 
 // Prints the value-comparison and its subiterator.
 func (it *Comparison) DebugString(indent int) string {
diff --git a/graph/leveldb/all_iterator.go b/graph/leveldb/all_iterator.go
index e9ab3c4..7a31f77 100644
--- a/graph/leveldb/all_iterator.go
+++ b/graph/leveldb/all_iterator.go
@@ -118,8 +118,8 @@ func (it *AllIterator) DebugString(indent int) string {
 	return fmt.Sprintf("%s(%s tags: %v leveldb size:%d %s %p)", strings.Repeat(" ", indent), it.Type(), it.Tags(), size, it.dir, it)
 }
 
-func (it *AllIterator) Type() string { return "all" }
-func (it *AllIterator) Sorted() bool { return false }
+func (it *AllIterator) Type() graph.Type { return graph.All }
+func (it *AllIterator) Sorted() bool     { return false }
 
 func (it *AllIterator) Optimize() (graph.Iterator, bool) {
 	return it, false
diff --git a/graph/leveldb/iterator.go b/graph/leveldb/iterator.go
index f6969e5..839a805 100644
--- a/graph/leveldb/iterator.go
+++ b/graph/leveldb/iterator.go
@@ -195,8 +195,16 @@ func (it *Iterator) DebugString(indent int) string {
 	return fmt.Sprintf("%s(%s %d tags: %v dir: %s size:%d %s)", strings.Repeat(" ", indent), it.Type(), it.UID(), it.Tags(), it.dir, size, it.ts.NameOf(it.checkId))
 }
 
-func (it *Iterator) Type() string { return "leveldb" }
-func (it *Iterator) Sorted() bool { return false }
+var levelDBType graph.Type
+
+func init() {
+	levelDBType = graph.Register("leveldb")
+}
+
+func Type() graph.Type { return levelDBType }
+
+func (it *Iterator) Type() graph.Type { return levelDBType }
+func (it *Iterator) Sorted() bool     { return false }
 
 func (it *Iterator) Optimize() (graph.Iterator, bool) {
 	return it, false
diff --git a/graph/leveldb/leveldb_test.go b/graph/leveldb/leveldb_test.go
index 9429927..6912bd7 100644
--- a/graph/leveldb/leveldb_test.go
+++ b/graph/leveldb/leveldb_test.go
@@ -160,7 +160,7 @@ func TestIterator(t *testing.T) {
 				size, accurate := it.Size()
 				So(size, ShouldBeBetween, 0, 20)
 				So(accurate, ShouldBeFalse)
-				So(it.Type(), ShouldEqual, "all")
+				So(it.Type(), ShouldEqual, graph.All)
 				re_it, ok := it.Optimize()
 				So(ok, ShouldBeFalse)
 				So(re_it, ShouldPointTo, it)
@@ -209,7 +209,7 @@ func TestIterator(t *testing.T) {
 				size, accurate := it.Size()
 				So(size, ShouldBeBetween, 0, 20)
 				So(accurate, ShouldBeFalse)
-				So(it.Type(), ShouldEqual, "all")
+				So(it.Type(), ShouldEqual, graph.All)
 				re_it, ok := it.Optimize()
 				So(ok, ShouldBeFalse)
 				So(re_it, ShouldPointTo, it)
@@ -407,7 +407,7 @@ func TestOptimize(t *testing.T) {
 				oldIt := lto.Clone()
 				newIt, ok := lto.Optimize()
 				So(ok, ShouldBeTrue)
-				So(newIt.Type(), ShouldEqual, "leveldb")
+				So(newIt.Type(), ShouldEqual, Type())
 
 				Convey("Containing the right things", func() {
 					afterOp := extractTripleFromIterator(ts, newIt)
diff --git a/graph/leveldb/triplestore_iterator_optimize.go b/graph/leveldb/triplestore_iterator_optimize.go
index 42a4082..2234060 100644
--- a/graph/leveldb/triplestore_iterator_optimize.go
+++ b/graph/leveldb/triplestore_iterator_optimize.go
@@ -21,7 +21,7 @@ import (
 
 func (ts *TripleStore) OptimizeIterator(it graph.Iterator) (graph.Iterator, bool) {
 	switch it.Type() {
-	case "linksto":
+	case graph.LinksTo:
 		return ts.optimizeLinksTo(it.(*iterator.LinksTo))
 
 	}
@@ -34,7 +34,7 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 		return it, false
 	}
 	primary := subs[0]
-	if primary.Type() == "fixed" {
+	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
 			val, ok := primary.Next()
diff --git a/graph/memstore/iterator.go b/graph/memstore/iterator.go
index 8df0e2e..b3bf9f4 100644
--- a/graph/memstore/iterator.go
+++ b/graph/memstore/iterator.go
@@ -101,12 +101,18 @@ func (it *Iterator) DebugString(indent int) string {
 	return fmt.Sprintf("%s(%s tags:%s size:%d %s)", strings.Repeat(" ", indent), it.Type(), it.Tags(), size, it.data)
 }
 
-func (it *Iterator) Type() string {
-	return "llrb"
-}
-func (it *Iterator) Sorted() bool {
-	return true
+var memType graph.Type
+
+func init() {
+	memType = graph.Register("llrb")
 }
+
+func Type() graph.Type { return memType }
+
+func (it *Iterator) Type() graph.Type { return memType }
+
+func (it *Iterator) Sorted() bool { return true }
+
 func (it *Iterator) Optimize() (graph.Iterator, bool) {
 	return it, false
 }
diff --git a/graph/memstore/triplestore_iterator_optimize.go b/graph/memstore/triplestore_iterator_optimize.go
index b48414c..1a89a16 100644
--- a/graph/memstore/triplestore_iterator_optimize.go
+++ b/graph/memstore/triplestore_iterator_optimize.go
@@ -21,7 +21,7 @@ import (
 
 func (ts *TripleStore) OptimizeIterator(it graph.Iterator) (graph.Iterator, bool) {
 	switch it.Type() {
-	case "linksto":
+	case graph.LinksTo:
 		return ts.optimizeLinksTo(it.(*iterator.LinksTo))
 
 	}
@@ -34,7 +34,7 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 		return it, false
 	}
 	primary := subs[0]
-	if primary.Type() == "fixed" {
+	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
 			val, ok := primary.Next()
diff --git a/graph/memstore/triplestore_test.go b/graph/memstore/triplestore_test.go
index 9dda9b2..d2e2bb2 100644
--- a/graph/memstore/triplestore_test.go
+++ b/graph/memstore/triplestore_test.go
@@ -105,7 +105,7 @@ func TestLinksToOptimization(t *testing.T) {
 	if !changed {
 		t.Error("Iterator didn't change")
 	}
-	if newIt.Type() != "llrb" {
+	if newIt.Type() != Type() {
 		t.Fatal("Didn't swap out to LLRB")
 	}
 	v := newIt.(*Iterator)
diff --git a/graph/mongo/iterator.go b/graph/mongo/iterator.go
index 4ebf890..4587b3c 100644
--- a/graph/mongo/iterator.go
+++ b/graph/mongo/iterator.go
@@ -157,12 +157,21 @@ func (it *Iterator) Size() (int64, bool) {
 	return it.size, true
 }
 
-func (it *Iterator) Type() string {
-	if it.isAll {
-		return "all"
-	}
-	return "mongo"
+var mongoType graph.Type
+
+func init() {
+	mongoType = graph.Register("mongo")
 }
+
+func Type() graph.Type { return mongoType }
+
+func (it *Iterator) Type() graph.Type {
+	if it.isAll {
+		return graph.All
+	}
+	return mongoType
+}
+
 func (it *Iterator) Sorted() bool                     { return true }
 func (it *Iterator) Optimize() (graph.Iterator, bool) { return it, false }
 
diff --git a/graph/mongo/triplestore_iterator_optimize.go b/graph/mongo/triplestore_iterator_optimize.go
index 7b8e7cc..766e84c 100644
--- a/graph/mongo/triplestore_iterator_optimize.go
+++ b/graph/mongo/triplestore_iterator_optimize.go
@@ -21,7 +21,7 @@ import (
 
 func (ts *TripleStore) OptimizeIterator(it graph.Iterator) (graph.Iterator, bool) {
 	switch it.Type() {
-	case "linksto":
+	case graph.LinksTo:
 		return ts.optimizeLinksTo(it.(*iterator.LinksTo))
 
 	}
@@ -34,7 +34,7 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 		return it, false
 	}
 	primary := subs[0]
-	if primary.Type() == "fixed" {
+	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
 			val, ok := primary.Next()
diff --git a/graph/sexp/parser_test.go b/graph/sexp/parser_test.go
index 4ae9c57..d6a3ba0 100644
--- a/graph/sexp/parser_test.go
+++ b/graph/sexp/parser_test.go
@@ -36,7 +36,7 @@ func TestParseSexpWithMemstore(t *testing.T) {
 
 		Convey("It should parse an empty query", func() {
 			it := BuildIteratorTreeForQuery(ts, "()")
-			So(it.Type(), ShouldEqual, "null")
+			So(it.Type(), ShouldEqual, graph.Null)
 		})
 
 		Convey("It should get a single triple linkage", func() {
@@ -44,7 +44,7 @@ func TestParseSexpWithMemstore(t *testing.T) {
 			query := "($a (:can \"win\"))"
 			So(len(query), ShouldEqual, 17)
 			it := BuildIteratorTreeForQuery(ts, query)
-			So(it.Type(), ShouldEqual, "and")
+			So(it.Type(), ShouldEqual, graph.And)
 			out, ok := it.Next()
 			So(ok, ShouldBeTrue)
 			So(out, ShouldEqual, ts.ValueOf("i"))
@@ -54,7 +54,7 @@ func TestParseSexpWithMemstore(t *testing.T) {
 			ts.AddTriple(&graph.Triple{"i", "can", "win", ""})
 			query := "(\"i\" (:can $a))"
 			it := BuildIteratorTreeForQuery(ts, query)
-			So(it.Type(), ShouldEqual, "and")
+			So(it.Type(), ShouldEqual, graph.And)
 			out, ok := it.Next()
 			So(ok, ShouldBeTrue)
 			So(out, ShouldEqual, ts.ValueOf("i"))
@@ -71,7 +71,7 @@ func TestTreeConstraintParse(t *testing.T) {
 		"(:like\n" +
 		"($a (:is :good))))"
 	it := BuildIteratorTreeForQuery(ts, query)
-	if it.Type() != "and" {
+	if it.Type() != graph.And {
 		t.Error("Odd iterator tree. Got: %s", it.DebugString(0))
 	}
 	out, ok := it.Next()
@@ -112,7 +112,7 @@ func TestMultipleConstraintParse(t *testing.T) {
 		"(:like :beer)\n" +
 		"(:like \"food\"))"
 	it := BuildIteratorTreeForQuery(ts, query)
-	if it.Type() != "and" {
+	if it.Type() != graph.And {
 		t.Error("Odd iterator tree. Got: %s", it.DebugString(0))
 	}
 	out, ok := it.Next()