diff --git a/graph/replication.go b/graph/replication.go
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+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package graph
+
+// Defines the interface for consistent replication of a graph instance.
+//
+// Separate from the backend, this dictates how individual triples get
+// identified and replicated consistently across (potentially) multiple
+// instances. The simplest case is to keep an append-only log of triple
+// changes.
+
+type Procedure byte
+
+const (
+	Add Procedure = iota
+	Delete
+)
+
+type Transaction struct {
+	Id     int64
+	Triple *Triple
+	Action Procedure
+}
+
+type Replication interface {
+	// Get a unique range of triple IDs from the Replication strategy.
+	// Returns the inclusive set of unique ids.
+	AcquireNextIds(size int64) (start int64, end int64)
+
+	// Returns the highest current ID.
+	GetLastId() int64
+
+	// Sends the transactions to the replicas.
+	Replicate([]*Transaction)
+
+	// Attempt to acquire the given range of triples from other replicated sources.
+	RequestTransactionRange(start int64, end int64)
+
+	// Opens the replication interface.
+	Open(TripleStore, Options)
+}