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+// itf/context-dep-itf.h
+
+// Copyright 2009-2011     Microsoft Corporation;  Go Vivace Inc.
+
+// See ../../COPYING for clarification regarding multiple authors
+//
+// 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
+//
+// THIS CODE IS PROVIDED *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
+// WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
+// MERCHANTABLITY OR NON-INFRINGEMENT.
+// See the Apache 2 License for the specific language governing permissions and
+// limitations under the License.
+
+
+#ifndef KALDI_ITF_CONTEXT_DEP_ITF_H_
+#define KALDI_ITF_CONTEXT_DEP_ITF_H_
+#include "base/kaldi-common.h"
+
+namespace kaldi {
+/// @ingroup tree_group
+/// @{
+
+/// context-dep-itf.h provides a link between
+/// the tree-building code in ../tree/, and the FST code in ../fstext/
+/// (particularly, ../fstext/context-dep.h).  It is an abstract
+/// interface that describes an object that can map from a
+/// phone-in-context to a sequence of integer leaf-ids.
+class ContextDependencyInterface {
+ public:
+  /// ContextWidth() returns the value N (e.g. 3 for triphone models) that says how many phones
+  ///   are considered for computing context.
+  virtual int ContextWidth() const = 0;
+
+  /// Central position P of the phone context, in 0-based numbering, e.g. P = 1 for typical
+  /// triphone system.  We have to see if we can do without this function.
+  virtual int CentralPosition() const = 0;
+
+  /// The "new" Compute interface.  For typical topologies,
+  /// pdf_class would be 0, 1, 2.
+  /// Returns success or failure; outputs the pdf-id.
+  ///
+  /// "Compute" is the main function of this interface, that takes a
+  /// sequence of N phones (and it must be N phones), possibly
+  /// including epsilons (symbol id zero) but only at positions other
+  /// than P [these represent unknown phone context due to end or
+  /// begin of sequence].  We do not insist that Compute must always
+  /// output (into stateseq) a nonempty sequence of states, but we
+  /// anticipate that stateseq will alyway be nonempty at output in
+  /// typical use cases.  "Compute" returns false if expansion somehow
+  /// failed.  Normally the calling code should raise an exception if
+  /// this happens.  We can define a different interface later in
+  /// order to handle other kinds of information-- the underlying
+  /// data-structures from event-map.h are very flexible.
+  virtual bool Compute(const std::vector<int32> &phoneseq, int32 pdf_class,
+                       int32 *pdf_id) const = 0;
+
+
+
+  /// NumPdfs() returns the number of acoustic pdfs (they are numbered 0.. NumPdfs()-1).
+  virtual int32 NumPdfs() const = 0;
+
+  virtual ~ContextDependencyInterface() {};
+  ContextDependencyInterface() {}
+
+  /// Returns pointer to new object which is copy of current one.
+  virtual ContextDependencyInterface *Copy() const = 0;
+ private:
+  KALDI_DISALLOW_COPY_AND_ASSIGN(ContextDependencyInterface);
+};
+/// @}
+}  // namespace Kaldi
+
+
+#endif