diff --git a/pkg/expr/graph.go b/pkg/expr/graph.go
index 15cbd81dd31..260af692e92 100644
--- a/pkg/expr/graph.go
+++ b/pkg/expr/graph.go
@@ -22,6 +22,17 @@ const (
 	TypeDatasourceNode
 )
 
+func (nt NodeType) String() string {
+	switch nt {
+	case TypeCMDNode:
+		return "Expression"
+	case TypeDatasourceNode:
+		return "Datasource"
+	default:
+		return "Unknown"
+	}
+}
+
 // Node is a node in a Data Pipeline. Node is either a expression command or a datasource query.
 type Node interface {
 	ID() int64 // ID() allows the gonum graph node interface to be fulfilled
@@ -181,6 +192,18 @@ func buildGraphEdges(dp *simple.DirectedGraph, registry map[string]Node) error {
 				return fmt.Errorf("can not add self referencing node for var '%v' ", neededVar)
 			}
 
+			if cmdNode.CMDType == TypeClassicConditions {
+				if neededNode.NodeType() != TypeDatasourceNode {
+					return fmt.Errorf("only data source queries may be inputs to a classic condition, %v is a %v", neededVar, neededNode.NodeType())
+				}
+			}
+
+			if neededNode.NodeType() == TypeCMDNode {
+				if neededNode.(*CMDNode).CMDType == TypeClassicConditions {
+					return fmt.Errorf("classic conditions may not be the input for other expressions, but %v is the input for %v", neededVar, cmdNode.RefID())
+				}
+			}
+
 			edge := dp.NewEdge(neededNode, cmdNode)
 
 			dp.SetEdge(edge)
diff --git a/pkg/expr/graph_test.go b/pkg/expr/graph_test.go
new file mode 100644
index 00000000000..3b7f0928578
--- /dev/null
+++ b/pkg/expr/graph_test.go
@@ -0,0 +1,220 @@
+package expr
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestServicebuildPipeLine(t *testing.T) {
+	var tests = []struct {
+		name              string
+		req               *Request
+		expectedOrder     []string
+		expectErrContains string
+	}{
+		{
+			name: "simple: a requires b",
+			req: &Request{
+				Queries: []Query{
+					{
+						RefID:         "A",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+							"expression": "B",
+							"reducer": "mean",
+							"type": "reduce"
+						}`),
+					},
+					{
+						RefID:         "B",
+						DatasourceUID: "Fake",
+					},
+				},
+			},
+			expectedOrder: []string{"B", "A"},
+		},
+		{
+			name: "cycle will error",
+			req: &Request{
+				Queries: []Query{
+					{
+						RefID:         "A",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+								"expression": "$B",
+								"type": "math"
+							}`),
+					},
+					{
+						RefID:         "B",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+								"expression": "$A",
+								"type": "math"
+							}`),
+					},
+				},
+			},
+			expectErrContains: "cyclic components",
+		},
+		{
+			name: "self reference will error",
+			req: &Request{
+				Queries: []Query{
+					{
+						RefID:         "A",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+								"expression": "$A",
+								"type": "math"
+							}`),
+					},
+				},
+			},
+			expectErrContains: "self referencing node",
+		},
+		{
+			name: "missing dependency will error",
+			req: &Request{
+				Queries: []Query{
+					{
+						RefID:         "A",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+								"expression": "$B",
+								"type": "math"
+							}`),
+					},
+				},
+			},
+			expectErrContains: "find dependent",
+		},
+		{
+			name: "classic can not take input from another expression",
+			req: &Request{
+				Queries: []Query{
+					{
+						RefID:         "A",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+							"type": "classic_conditions",
+							"conditions": [
+								{
+									"evaluator": {
+									"params": [
+										2,
+										3
+									],
+									"type": "within_range"
+									},
+									"operator": {
+									"type": "or"
+									},
+									"query": {
+									"params": [
+										"B"
+									]
+									},
+									"reducer": {
+									"params": [],
+									"type": "diff"
+									},
+									"type": "query"
+								}
+							]
+						}`),
+					},
+					{
+						RefID:         "B",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+							"expression": "C",
+							"reducer": "mean",
+							"type": "reduce"
+						}`),
+					},
+					{
+						RefID:         "C",
+						DatasourceUID: "Fake",
+					},
+				},
+			},
+			expectErrContains: "only data source queries may be inputs to a classic condition",
+		},
+		{
+			name: "classic can not output to another expression",
+			req: &Request{
+				Queries: []Query{
+					{
+						RefID:         "A",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+							"type": "classic_conditions",
+							"conditions": [
+								{
+									"evaluator": {
+									"params": [
+										2,
+										3
+									],
+									"type": "within_range"
+									},
+									"operator": {
+									"type": "or"
+									},
+									"query": {
+									"params": [
+										"C"
+									]
+									},
+									"reducer": {
+									"params": [],
+									"type": "diff"
+									},
+									"type": "query"
+								}
+							]
+						}`),
+					},
+					{
+						RefID:         "B",
+						DatasourceUID: DatasourceUID,
+						JSON: json.RawMessage(`{
+							"expression": "A",
+							"reducer": "mean",
+							"type": "reduce"
+						}`),
+					},
+					{
+						RefID:         "C",
+						DatasourceUID: "Fake",
+					},
+				},
+			},
+			expectErrContains: "classic conditions may not be the input for other expressions",
+		},
+	}
+	s := Service{}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nodes, err := s.buildPipeline(tt.req)
+			if tt.expectErrContains != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), tt.expectErrContains)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, tt.expectedOrder, getRefIDOrder(nodes))
+			}
+		})
+	}
+}
+
+func getRefIDOrder(nodes []Node) []string {
+	ids := make([]string, 0, len(nodes))
+	for _, n := range nodes {
+		ids = append(ids, n.RefID())
+	}
+	return ids
+}
diff --git a/pkg/expr/nodes.go b/pkg/expr/nodes.go
index d47429bc4c9..59cfa31ffbf 100644
--- a/pkg/expr/nodes.go
+++ b/pkg/expr/nodes.go
@@ -98,6 +98,7 @@ func buildCMDNode(dp *simple.DirectedGraph, rn *rawNode) (*CMDNode, error) {
 			id:    dp.NewNode().ID(),
 			refID: rn.RefID,
 		},
+		CMDType: commandType,
 	}
 
 	switch commandType {