[ONNX] add the ability to register custom ONNX operators (#1856)

* onnx: add information about a domain to operators set
Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

* onnx: updates after review
Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

* onnx: update comments in the code
Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

* onnx: fix bug in node's description method
Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

* onnx: fix CentOS compilation
Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

* onnx: more after review changes
Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

src/ngraph/frontend/onnx_import/CMakeLists.txt

@@ -18,7 +18,10 @@ set(ONNX_OPSET_VERSION 9 CACHE INTERNAL "Supported version of ONNX operator set"
 
 add_library(onnx_import_interface OBJECT
         onnx.cpp
-        onnx.hpp)
+        onnx.hpp
+        core/operator_set.hpp
+        core/node.cpp
+        core/node.hpp)
 
 add_library(onnx_import STATIC
         core/attribute.cpp
@@ -27,7 +30,6 @@ add_library(onnx_import STATIC
         core/graph.hpp
         core/model.cpp
         core/model.hpp
-        core/node.cpp
         core/node.hpp
         core/operator_set.hpp
         core/tensor.hpp

src/ngraph/frontend/onnx_import/core/attribute.cpp

@@ -16,25 +16,25 @@
 
 #include "attribute.hpp"
 #include "graph.hpp"
-#include "operator_set.hpp"
+#include "model.hpp"
 
 namespace ngraph
 {
     namespace onnx_import
     {
-        std::vector<Graph> Attribute::get_graph_array(const OperatorSet& opset) const
+        std::vector<Graph> Attribute::get_graph_array(const Model& model) const
         {
             std::vector<Graph> result;
             for (const auto& graph : m_attribute_proto->graphs())
             {
-                result.emplace_back(graph, opset);
+                result.emplace_back(graph, model);
             }
             return result;
         }
 
-        Graph Attribute::get_graph(const OperatorSet& opset) const
+        Graph Attribute::get_graph(const Model& model) const
         {
-            return Graph{m_attribute_proto->g(), opset};
+            return Graph{m_attribute_proto->g(), model};
         }
 
     } // namespace onnx_import

src/ngraph/frontend/onnx_import/core/attribute.hpp

@@ -20,15 +20,15 @@
 
 #include "ngraph/except.hpp"
 
-#include "operator_set.hpp"
 #include "tensor.hpp"
 
 namespace ngraph
 {
     namespace onnx_import
     {
-        // forward declaration
+        // forward declarations
         class Graph;
+        class Model;
 
         namespace error
         {
@@ -272,7 +272,7 @@ namespace ngraph
             float get_float() const { return m_attribute_proto->f(); }
             int64_t get_integer() const { return m_attribute_proto->i(); }
             const std::string& get_string() const { return m_attribute_proto->s(); }
-            Graph get_graph(const OperatorSet& opset) const;
+            Graph get_graph(const Model&) const;
 
             std::vector<Tensor> get_tensor_array() const
             {
@@ -297,7 +297,7 @@ namespace ngraph
                         std::end(m_attribute_proto->strings())};
             }
 
-            std::vector<Graph> get_graph_array(const OperatorSet&) const;
+            std::vector<Graph> get_graph_array(const Model&) const;
 
             /* explicit */ operator onnx::AttributeProto_AttributeType() const
             {

src/ngraph/frontend/onnx_import/core/graph.cpp

@@ -34,11 +34,17 @@ namespace ngraph
                 }
                 return result;
             }
+
+            inline std::string to_string(const onnx::NodeProto& node_proto)
+            {
+                return (node_proto.domain().empty() ? "" : node_proto.domain() + ".") +
+                       node_proto.op_type();
+            }
         }
 
-        Graph::Graph(const onnx::GraphProto& graph_proto, const OperatorSet& opset)
+        Graph::Graph(const onnx::GraphProto& graph_proto, const Model& model)
             : m_graph_proto{&graph_proto}
-            , m_opset{&opset}
+            , m_model{&model}
         {
             for (const auto& tensor : m_graph_proto->initializer())
             {
@@ -65,10 +71,9 @@ namespace ngraph
             std::set<std::string> unknown_operator_types;
             for (const auto& node_proto : m_graph_proto->node())
             {
-                auto it = m_opset->find(node_proto.op_type());
-                if (it == std::end(*m_opset))
+                if (!m_model->is_operator_available(node_proto))
                 {
-                    unknown_operator_types.emplace(node_proto.op_type());
+                    unknown_operator_types.emplace(detail::to_string(node_proto));
                 }
             }
 
@@ -78,7 +83,7 @@ namespace ngraph
             // Process ONNX graph nodes, convert to nGraph nodes
             for (const auto& node_proto : m_graph_proto->node())
             {
-                m_nodes.emplace_back(node_proto, this);
+                m_nodes.emplace_back(node_proto, *this);
                 const Node& node{m_nodes.back()};
                 NodeVector ng_nodes{node.get_ng_nodes()};
                 for (int i = 0; i < ng_nodes.size(); i++)

src/ngraph/frontend/onnx_import/core/graph.hpp

@@ -23,6 +23,7 @@
 
 #include "ngraph/op/parameter_vector.hpp"
 
+#include "model.hpp"
 #include "operator_set.hpp"
 #include "value_info.hpp"
 
@@ -33,7 +34,7 @@ namespace ngraph
         class Graph
         {
         public:
-            explicit Graph(const onnx::GraphProto& proto, const OperatorSet& opset);
+            Graph(const onnx::GraphProto& proto, const Model& model);
 
             const std::vector<Node>& get_nodes() const { return m_nodes; }
             const std::vector<ValueInfo>& get_inputs() const { return m_inputs; }
@@ -47,7 +48,7 @@ namespace ngraph
             const std::string& get_name() const { return m_graph_proto->name(); }
             NodeVector make_ng_nodes(const Node& node) const
             {
-                return m_opset->at(node.op_type())(node);
+                return m_model->get_operator(node.op_type(), node.domain())(node);
             }
 
         private:
@@ -58,7 +59,7 @@ namespace ngraph
             op::ParameterVector m_parameters;
             std::map<std::string, std::shared_ptr<ngraph::Node>> m_ng_node_cache;
             std::map<std::string, Tensor> m_initializers;
-            const OperatorSet* m_opset;
+            const Model* m_model;
         };
 
         inline std::ostream& operator<<(std::ostream& outs, const Graph& graph)

src/ngraph/frontend/onnx_import/core/model.cpp

@@ -17,6 +17,7 @@
 #include <onnx-ml.pb.h>
 
 #include "model.hpp"
+#include "ops_bridge.hpp"
 
 namespace ngraph
 {
@@ -25,15 +26,49 @@ namespace ngraph
         Model::Model(const onnx::ModelProto& model_proto)
             : m_model_proto{&model_proto}
         {
+            // Walk through the elements of opset_import field and register operator sets
+            // for each domain. An exception UnknownDomain() will raise if the domain is
+            // unknown or invalid.
             for (const auto& id : m_model_proto->opset_import())
             {
-                // onnx.proto(.3): the empty string ("") or absence of this field implies
-                // the operator set that is defined as part of the ONNX specification.
-                if (id.domain().empty())
+                m_opset.emplace(id.domain(),
+                                OperatorsBridge::get_operator_set(
+                                    id.version(), (id.domain() == "ai.onnx" ? "" : id.domain())));
+            }
+            // onnx.proto(.3): the empty string ("") for domain or absence of opset_import field
+            // implies the operator set that is defined as part of the ONNX specification.
+            const auto dm = m_opset.find("");
+            if (dm == std::end(m_opset))
+            {
+                m_opset.emplace("", OperatorsBridge::get_operator_set(ONNX_OPSET_VERSION, ""));
+            }
+        }
+
+        const Operator& Model::get_operator(const std::string& name,
+                                            const std::string& domain) const
+        {
+            const auto dm = m_opset.find(domain);
+            if (dm == std::end(m_opset))
             {
-                    m_opset_version = id.version();
+                throw error::UnknownDomain{domain};
             }
+            const auto op = dm->second.find(name);
+            if (op == std::end(dm->second))
+            {
+                throw error::UnknownOperator{name, domain};
+            }
+            return op->second;
+        }
+
+        bool Model::is_operator_available(const onnx::NodeProto& node_proto) const
+        {
+            const auto dm = m_opset.find(node_proto.domain());
+            if (dm == std::end(m_opset))
+            {
+                return false;
             }
+            const auto op = dm->second.find(node_proto.op_type());
+            return (op != std::end(dm->second));
         }
 
     } // namespace onnx_import

src/ngraph/frontend/onnx_import/core/model.hpp

@@ -16,9 +16,13 @@
 
 #pragma once
 
+#include <onnx-ml.pb.h>
+
 #include <ostream>
+#include <string>
+#include <unordered_map>
 
-#include <onnx-ml.pb.h>
+#include "operator_set.hpp"
 
 namespace ngraph
 {
@@ -30,11 +34,11 @@ namespace ngraph
             Model() = delete;
             explicit Model(const onnx::ModelProto& model_proto);
 
-            Model(Model&&) noexcept = default;
             Model(const Model&) = default;
+            Model(Model&&) = default;
 
-            Model& operator=(Model&&) noexcept = delete;
             Model& operator=(const Model&) = delete;
+            Model& operator=(Model&&) = delete;
 
             const std::string& get_producer_name() const { return m_model_proto->producer_name(); }
             const onnx::GraphProto& get_graph() const { return m_model_proto->graph(); }
@@ -44,10 +48,23 @@ namespace ngraph
                 return m_model_proto->producer_version();
             }
 
-            std::int64_t get_opset_version() const { return m_opset_version; }
+            /// \brief Access an operator object by its type name and domain name
+            /// The function will return the operator object if it exists, or report an error
+            /// in case of domain or operator absence.
+            /// \param name       type name of the operator object,
+            /// \param domain     domain name of the operator object.
+            /// \return Reference to the operator object.
+            /// \throw error::UnknownDomain    there is no operator set defined for the given domain,
+            /// \throw error::UnknownOperator  the given operator type name does not exist in operator set.
+            const Operator& get_operator(const std::string& name, const std::string& domain) const;
+
+            /// \brief Check availability of operator base on NodeProto.
+            /// \return `true` if the operator is available, otherwise it returns `false`.
+            bool is_operator_available(const onnx::NodeProto& node_proto) const;
+
         private:
             const onnx::ModelProto* m_model_proto;
-            std::int64_t m_opset_version{ONNX_OPSET_VERSION};
+            std::unordered_map<std::string, OperatorSet> m_opset;
         };
 
         inline std::ostream& operator<<(std::ostream& outs, const Model& model)

src/ngraph/frontend/onnx_import/core/node.cpp

@@ -14,15 +14,110 @@
 // limitations under the License.
 //*****************************************************************************
 
-#include "node.hpp"
+#include <onnx-ml.pb.h>
+
+#include "attribute.hpp"
 #include "graph.hpp"
+#include "node.hpp"
+#include "tensor.hpp"
 
 namespace ngraph
 {
     namespace onnx_import
     {
-        NodeVector Node::get_ng_nodes() const { return m_graph->make_ng_nodes(*this); }
-        NodeVector Node::get_ng_inputs() const
+        class Node::Impl
+        {
+        public:
+            Impl() = delete;
+
+            Impl(const onnx::NodeProto& node_proto, const Graph& graph)
+                : m_node_proto{&node_proto}
+                , m_graph{&graph}
+                , m_attributes{std::begin(node_proto.attribute()), std::end(node_proto.attribute())}
+                , m_output_names{std::begin(node_proto.output()), std::end(node_proto.output())}
+            {
+            }
+
+            const std::vector<Attribute>& attributes() const;
+            NodeVector get_ng_nodes(const Node& node) const;
+            NodeVector get_ng_inputs() const;
+
+            const std::string& domain() const;
+            const std::string& op_type() const;
+            const std::string& name() const;
+
+            const std::string& description() const;
+            const std::vector<std::reference_wrapper<const std::string>>& get_output_names() const;
+            const std::string& output(int index) const;
+
+            template <typename T>
+            T get_attribute_value(const std::string& name, T default_value) const;
+
+            template <typename T>
+            T get_attribute_value(const std::string& name) const;
+
+            const onnx::NodeProto& node_proto() const;
+            const Graph& graph() const;
+
+        private:
+            const onnx::NodeProto* m_node_proto;
+            const Graph* m_graph;
+            std::vector<Attribute> m_attributes;
+            std::vector<std::reference_wrapper<const std::string>> m_output_names;
+            mutable std::string m_description;
+        };
+
+        const onnx::NodeProto& Node::Impl::node_proto() const { return *m_node_proto; }
+        const Graph& Node::Impl::graph() const { return *m_graph; }
+        const std::vector<Attribute>& Node::Impl::attributes() const { return m_attributes; }
+        const std::string& Node::Impl::domain() const { return m_node_proto->domain(); }
+        const std::string& Node::Impl::op_type() const { return m_node_proto->op_type(); }
+        const std::string& Node::Impl::name() const { return m_node_proto->name(); }
+        const std::vector<std::reference_wrapper<const std::string>>&
+            Node::Impl::get_output_names() const
+        {
+            return m_output_names;
+        }
+
+        const std::string& Node::Impl::output(int index) const
+        {
+            return m_node_proto->output(index);
+        }
+
+        template <typename T>
+        T Node::Impl::get_attribute_value(const std::string& name, T default_value) const
+        {
+            auto it = std::find_if(
+                std::begin(m_attributes), std::end(m_attributes), [&](const Attribute& attribute) {
+                    return attribute.get_name() == name;
+                });
+            if (it == std::end(m_attributes))
+            {
+                return std::forward<T>(default_value);
+            }
+            return it->template get_value<T>();
+        }
+
+        template <typename T>
+        T Node::Impl::get_attribute_value(const std::string& name) const
+        {
+            auto it = std::find_if(
+                std::begin(m_attributes), std::end(m_attributes), [&](const Attribute& attribute) {
+                    return attribute.get_name() == name;
+                });
+            if (it == std::end(m_attributes))
+            {
+                throw error::node::UnknownAttribute{this->name(), name};
+            }
+            return it->template get_value<T>();
+        }
+
+        NodeVector Node::Impl::get_ng_nodes(const Node& node) const
+        {
+            return m_graph->make_ng_nodes(node);
+        }
+
+        NodeVector Node::Impl::get_ng_inputs() const
         {
             NodeVector result;
             for (const auto& name : m_node_proto->input())
@@ -32,20 +127,224 @@ namespace ngraph
             return result;
         }
 
-        std::string Node::get_description() const
+        const std::string& Node::Impl::description() const
+        {
+            if (m_description.empty())
             {
-            if (!get_name().empty())
+                if (!name().empty())
                 {
-                return get_name();
+                    m_description = name();
                 }
-
-            std::stringstream stream;
+                else
+                {
                     for (std::size_t index = 0; index < m_output_names.size(); ++index)
                     {
-                stream << (index != 0 ? ", " : "");
-                stream << m_output_names.at(index).get();
+                        m_description += (index != 0 ? ", " : "") + m_output_names.at(index).get();
+                    }
+                }
+            }
+            return m_description;
+        }
+
+        Node::Node(const onnx::NodeProto& node_proto, const Graph& graph)
+            : m_pimpl{new Impl{node_proto, graph}, [](Impl* impl) { delete impl; }}
+        {
+        }
+
+        Node::Node(Node&& other) noexcept
+            : m_pimpl{std::move(other.m_pimpl)}
+        {
+        }
+
+        Node::Node(const Node& other)
+            : m_pimpl{new Impl{other.m_pimpl->node_proto(), other.m_pimpl->graph()},
+                      [](Impl* impl) { delete impl; }}
+        {
         }
-            return stream.str();
+
+        NodeVector Node::get_ng_inputs() const { return m_pimpl->get_ng_inputs(); }
+        NodeVector Node::get_ng_nodes() const { return m_pimpl->get_ng_nodes(*this); }
+        const std::string& Node::domain() const { return m_pimpl->domain(); }
+        const std::string& Node::op_type() const { return m_pimpl->op_type(); }
+        const std::string& Node::get_description() const { return m_pimpl->description(); }
+        const std::string& Node::get_name() const { return m_pimpl->name(); }
+        const std::vector<std::reference_wrapper<const std::string>>& Node::get_output_names() const
+        {
+            return m_pimpl->get_output_names();
+        }
+
+        const std::string& Node::output(int index) const { return m_pimpl->output(index); }
+        template <>
+        float Node::get_attribute_value(const std::string& name, float default_value) const
+        {
+            return m_pimpl->template get_attribute_value<float>(name, default_value);
+        }
+
+        template <>
+        double Node::get_attribute_value(const std::string& name, double default_value) const
+        {
+            return m_pimpl->template get_attribute_value<double>(name, default_value);
+        }
+
+        template <>
+        std::int64_t Node::get_attribute_value(const std::string& name,
+                                               std::int64_t default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::int64_t>(name, default_value);
+        }
+
+        template <>
+        std::string Node::get_attribute_value(const std::string& name,
+                                              std::string default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::string>(name,
+                                                                      std::move(default_value));
+        }
+
+        template <>
+        Tensor Node::get_attribute_value(const std::string& name, Tensor default_value) const
+        {
+            return m_pimpl->template get_attribute_value<Tensor>(name, std::move(default_value));
+        }
+
+        template <>
+        Graph Node::get_attribute_value(const std::string& name, Graph default_value) const
+        {
+            return m_pimpl->template get_attribute_value<Graph>(name, std::move(default_value));
+        }
+
+        template <>
+        std::vector<float> Node::get_attribute_value(const std::string& name,
+                                                     std::vector<float> default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<float>>(
+                name, std::move(default_value));
+        }
+
+        template <>
+        std::vector<double> Node::get_attribute_value(const std::string& name,
+                                                      std::vector<double> default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<double>>(
+                name, std::move(default_value));
+        }
+
+        template <>
+        std::vector<std::int64_t>
+            Node::get_attribute_value(const std::string& name,
+                                      std::vector<std::int64_t> default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<std::int64_t>>(
+                name, std::move(default_value));
+        }
+
+        template <>
+        std::vector<std::size_t>
+            Node::get_attribute_value(const std::string& name,
+                                      std::vector<std::size_t> default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<std::size_t>>(
+                name, std::move(default_value));
+        }
+
+        template <>
+        std::vector<Tensor> Node::get_attribute_value(const std::string& name,
+                                                      std::vector<Tensor> default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<Tensor>>(
+                name, std::move(default_value));
+        }
+
+        template <>
+        std::vector<Graph> Node::get_attribute_value(const std::string& name,
+                                                     std::vector<Graph> default_value) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<Graph>>(
+                name, std::move(default_value));
+        }
+
+        template <>
+        float Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<float>(name);
+        }
+
+        template <>
+        double Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<double>(name);
+        }
+
+        template <>
+        std::int64_t Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::int64_t>(name);
+        }
+
+        template <>
+        std::size_t Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::size_t>(name);
+        }
+
+        template <>
+        std::string Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::string>(name);
+        }
+
+        template <>
+        Tensor Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<Tensor>(name);
+        }
+
+        template <>
+        Graph Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<Graph>(name);
+        }
+
+        template <>
+        std::vector<float> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<float>>(name);
+        }
+
+        template <>
+        std::vector<double> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<double>>(name);
+        }
+
+        template <>
+        std::vector<std::int64_t> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<std::int64_t>>(name);
+        }
+
+        template <>
+        std::vector<std::size_t> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<std::size_t>>(name);
+        }
+
+        template <>
+        std::vector<std::string> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<std::string>>(name);
+        }
+
+        template <>
+        std::vector<Tensor> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<Tensor>>(name);
+        }
+
+        template <>
+        std::vector<Graph> Node::get_attribute_value(const std::string& name) const
+        {
+            return m_pimpl->template get_attribute_value<std::vector<Graph>>(name);
         }
 
     } // namespace onnx_import

src/ngraph/frontend/onnx_import/core/node.hpp

@@ -18,12 +18,14 @@
 
 #include <string>
 
-#include <onnx-ml.pb.h>
-
+#include "ngraph/except.hpp"
 #include "ngraph/node_vector.hpp"
 
-#include "attribute.hpp"
-#include "tensor.hpp"
+namespace onnx
+{
+    // forward declaration
+    class NodeProto;
+}
 
 namespace ngraph
 {
@@ -52,70 +54,41 @@ namespace ngraph
         {
         public:
             Node() = delete;
-            Node(const onnx::NodeProto& node_proto, const Graph* graph)
-                : m_node_proto{&node_proto}
-                , m_graph{graph}
-                , m_attributes{std::begin(node_proto.attribute()), std::end(node_proto.attribute())}
-                , m_output_names{std::begin(node_proto.output()), std::end(node_proto.output())}
-            {
-            }
+            Node(const onnx::NodeProto& node_proto, const Graph& graph);
 
-            Node(Node&&) noexcept = default;
-            Node(const Node&) = default;
+            Node(Node&&) noexcept;
+            Node(const Node&);
 
             Node& operator=(Node&&) noexcept = delete;
             Node& operator=(const Node&) = delete;
 
-            const std::vector<Attribute>& attributes() const { return m_attributes; }
-            NodeVector get_ng_nodes() const;
             NodeVector get_ng_inputs() const;
+            NodeVector get_ng_nodes() const;
+            const std::string& domain() const;
+            const std::string& op_type() const;
+            const std::string& get_name() const;
 
-            const std::string& domain() const { return m_node_proto->domain(); }
-            const std::string& op_type() const { return m_node_proto->op_type(); }
-            const std::string& get_name() const { return m_node_proto->name(); }
-            /// @brief Describe the ONNX Node to make debugging graphs easier
+            /// \brief Describe the ONNX Node to make debugging graphs easier
             /// Function will return the Node's name if it has one, or the names of its outputs.
             /// \return Description of Node
-            std::string get_description() const;
+            const std::string& get_description() const;
+
+            const std::vector<std::reference_wrapper<const std::string>>& get_output_names() const;
+            const std::string& output(int index) const;
 
-            const std::vector<std::reference_wrapper<const std::string>>& get_output_names() const
-            {
-                return m_output_names;
-            }
-            const std::string& output(int index) const { return m_node_proto->output(index); }
             template <typename T>
-            T get_attribute_value(const std::string& name, T default_value) const
-            {
-                auto it = std::find_if(
-                    std::begin(m_attributes),
-                    std::end(m_attributes),
-                    [&](const Attribute& attribute) { return attribute.get_name() == name; });
-                if (it == std::end(m_attributes))
-                {
-                    return default_value;
-                }
-                return it->template get_value<T>();
-            }
+            T get_attribute_value(const std::string& name, T default_value) const;
 
             template <typename T>
-            T get_attribute_value(const std::string& name) const
-            {
-                auto it = std::find_if(
-                    std::begin(m_attributes),
-                    std::end(m_attributes),
-                    [&](const Attribute& attribute) { return attribute.get_name() == name; });
-                if (it == std::end(m_attributes))
-                {
-                    throw error::node::UnknownAttribute{get_name(), name};
-                }
-                return it->template get_value<T>();
-            }
+            T get_attribute_value(const std::string& name) const;
 
         private:
-            const onnx::NodeProto* m_node_proto;
-            const Graph* m_graph;
-            std::vector<Attribute> m_attributes;
-            std::vector<std::reference_wrapper<const std::string>> m_output_names;
+            class Impl;
+            // In this case we need custom deleter, because Impl is an incomplete
+            // type. Node's are elements of std::vector. Without custom deleter
+            // compilation fails; the compiler is unable to parameterize an allocator's
+            // default deleter due to incomple type.
+            std::unique_ptr<Impl, void (*)(Impl*)> m_pimpl;
         };
 
         inline std::ostream& operator<<(std::ostream& outs, const Node& node)

src/ngraph/frontend/onnx_import/core/operator_set.hpp

@@ -22,13 +22,12 @@
 
 #include "ngraph/node_vector.hpp"
 
+#include "node.hpp"
+
 namespace ngraph
 {
     namespace onnx_import
     {
-        // Forward declaration
-        class Node;
-
         using Operator = std::function<NodeVector(const Node&)>;
         using OperatorSet = std::unordered_map<std::string, std::reference_wrapper<const Operator>>;
 

src/ngraph/frontend/onnx_import/onnx.cpp

@@ -61,8 +61,7 @@ namespace ngraph
             }
             std::vector<std::shared_ptr<Function>> output_functions;
             Model model{model_proto};
-            Graph graph{model_proto.graph(),
-                        OperatorsBridge::get_operator_set(model.get_opset_version())};
+            Graph graph{model_proto.graph(), model};
             for (const auto& output : graph.get_outputs())
             {
                 output_functions.emplace_back(std::make_shared<Function>(
@@ -91,6 +90,14 @@ namespace ngraph
             return load_onnx_model(path).front();
         }
 
+        void register_operator(const std::string& name,
+                               std::int64_t version,
+                               const std::string& domain,
+                               Operator fn)
+        {
+            OperatorsBridge::register_operator(name, version, domain, std::move(fn));
+        }
+
     } // namespace onnx_import
 
 } // namespace ngraph

src/ngraph/frontend/onnx_import/onnx.hpp

@@ -21,10 +21,18 @@
 
 #include "ngraph/function.hpp"
 
+#include "core/operator_set.hpp"
+
 namespace ngraph
 {
     namespace onnx_import
     {
+        // Registers ONNX custom operator
+        void register_operator(const std::string& name,
+                               std::int64_t version,
+                               const std::string& domain,
+                               Operator fn);
+
         // Convert on ONNX model to a vector of nGraph Functions (input stream)
         std::vector<std::shared_ptr<Function>> load_onnx_model(std::istream&);
 

src/ngraph/frontend/onnx_import/ops_bridge.cpp

@@ -87,134 +87,51 @@ namespace ngraph
 {
     namespace onnx_import
     {
-        const OperatorSet& OperatorsBridge::get_operator_set_version_1() const
+        namespace detail
         {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
+            const Operator& find(const std::string& name,
+                                 std::int64_t version,
+                                 const std::string& domain,
+                                 const std::map<std::int64_t, Operator>& map)
             {
-                for (const auto& op : m_map)
+                while (version > 0)
                 {
-                    for (const auto& it : op.second)
+                    const auto it = map.find(version--);
+                    if (it != std::end(map))
                     {
-                        if (it.first == 1)
-                        {
-                            operator_set.emplace(op.first, it.second);
-                        }
+                        return it->second;
                     }
                 }
+                throw error::UnsupportedVersion{name, version, domain};
             }
-            return operator_set;
         }
 
-        const OperatorSet& OperatorsBridge::get_operator_set_version_2() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
+        void OperatorsBridge::_register_operator(const std::string& name,
+                                                 std::int64_t version,
+                                                 const std::string& domain,
+                                                 Operator fn)
         {
-                operator_set = get_operator_set_version_1();
-            }
-            return operator_set;
+            m_map[domain][name].emplace(version, std::move(fn));
         }
 
-        const OperatorSet& OperatorsBridge::get_operator_set_version_3() const
+        OperatorSet OperatorsBridge::_get_operator_set(std::int64_t version,
+                                                       const std::string& domain)
         {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
+            OperatorSet result;
+            auto dm = m_map.find(domain);
+            if (dm == std::end(m_map))
             {
-                operator_set = get_operator_set_version_2();
-            }
-            return operator_set;
+                throw error::UnknownDomain{domain};
             }
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version_4() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
-            {
-                operator_set = get_operator_set_version_3();
-            }
-            return operator_set;
-        }
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version_5() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
-            {
-                operator_set = get_operator_set_version_4();
-            }
-            return operator_set;
-        }
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version_6() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
-            {
-                operator_set = get_operator_set_version_5();
-            }
-            return operator_set;
-        }
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version_7() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
-            {
-                operator_set = get_operator_set_version_6();
-            }
-            return operator_set;
-        }
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version_8() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
-            {
-                operator_set = get_operator_set_version_7();
-            }
-            return operator_set;
-        }
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version_9() const
-        {
-            static OperatorSet operator_set;
-            if (operator_set.empty())
-            {
-                operator_set = get_operator_set_version_8();
-            }
-            return operator_set;
-        }
-
-#define OPERATOR_SET_NAME(version_) get_operator_set_version_##version_()
-
-#define GET_OPERATOR_SET(version_)                                                                 \
-    case version_:                                                                                 \
-        return OPERATOR_SET_NAME(version_)
-
-#define OPERATOR_SET_NAME_HELPER(version_) OPERATOR_SET_NAME(version_)
-
-#define DEFAULT_OPERATOR_SET() return OPERATOR_SET_NAME_HELPER(ONNX_OPSET_VERSION)
-
-        const OperatorSet& OperatorsBridge::get_operator_set_version(std::int64_t version) const
-        {
-            switch (version)
+            for (const auto& op : dm->second)
             {
-                GET_OPERATOR_SET(1);
-                GET_OPERATOR_SET(2);
-                GET_OPERATOR_SET(3);
-                GET_OPERATOR_SET(4);
-                GET_OPERATOR_SET(5);
-                GET_OPERATOR_SET(6);
-                GET_OPERATOR_SET(7);
-                GET_OPERATOR_SET(8);
-                GET_OPERATOR_SET(9);
-            default: DEFAULT_OPERATOR_SET();
+                result.emplace(op.first, detail::find(op.first, version, domain, op.second));
             }
+            return result;
         }
 
-#define REGISTER_OPERATOR(name_, version_, fn_)                                                    \
-    m_map[name_].emplace(version_, std::bind(op::set_##version_::fn_, std::placeholders::_1))
+#define REGISTER_OPERATOR(name_, ver_, fn_)                                                        \
+    m_map[""][name_].emplace(ver_, std::bind(op::set_##ver_::fn_, std::placeholders::_1))
 
         OperatorsBridge::OperatorsBridge()
         {

src/ngraph/frontend/onnx_import/ops_bridge.hpp

@@ -33,16 +33,27 @@ namespace ngraph
         {
             struct UnknownOperator : ngraph_error
             {
-                explicit UnknownOperator(const std::string& op_type)
-                    : ngraph_error{"unknown operator: \"" + op_type + "\""}
+                UnknownOperator(const std::string& name, const std::string& domain)
+                    : ngraph_error{(domain.empty() ? "" : domain + ".") + name}
+                {
+                }
+            };
+
+            struct UnknownDomain : ngraph_error
+            {
+                explicit UnknownDomain(const std::string& domain)
+                    : ngraph_error{domain}
                 {
                 }
             };
 
             struct UnsupportedVersion : ngraph_error
             {
-                explicit UnsupportedVersion(std::int64_t version)
-                    : ngraph_error{"unsupported operator set version: " + std::to_string(version)}
+                UnsupportedVersion(const std::string& name,
+                                   std::int64_t version,
+                                   const std::string& domain)
+                    : ngraph_error{(domain.empty() ? "" : domain + ".") + name + ":" +
+                                   std::to_string(version)}
                 {
                 }
             };
@@ -57,32 +68,37 @@ namespace ngraph
             OperatorsBridge(OperatorsBridge&&) = delete;
             OperatorsBridge& operator=(OperatorsBridge&&) = delete;
 
-            static const OperatorSet& get_operator_set(std::int64_t version)
+            static OperatorSet get_operator_set(std::int64_t version, const std::string& domain)
+            {
+                return instance()._get_operator_set(version, domain);
+            }
+
+            static void register_operator(const std::string& name,
+                                          std::int64_t version,
+                                          const std::string& domain,
+                                          Operator fn)
             {
-                return instance().get_operator_set_version(version);
+                instance()._register_operator(name, version, domain, std::move(fn));
             }
 
         private:
-            std::unordered_map<std::string, std::map<std::int64_t, Operator>> m_map;
+            std::unordered_map<std::string,
+                               std::unordered_map<std::string, std::map<std::int64_t, Operator>>>
+                m_map;
 
             OperatorsBridge();
 
-            static const OperatorsBridge& instance()
+            static OperatorsBridge& instance()
             {
                 static OperatorsBridge instance;
                 return instance;
             }
 
-            const OperatorSet& get_operator_set_version_1() const;
-            const OperatorSet& get_operator_set_version_2() const;
-            const OperatorSet& get_operator_set_version_3() const;
-            const OperatorSet& get_operator_set_version_4() const;
-            const OperatorSet& get_operator_set_version_5() const;
-            const OperatorSet& get_operator_set_version_6() const;
-            const OperatorSet& get_operator_set_version_7() const;
-            const OperatorSet& get_operator_set_version_8() const;
-            const OperatorSet& get_operator_set_version_9() const;
-            const OperatorSet& get_operator_set_version(std::int64_t version) const;
+            void _register_operator(const std::string& name,
+                                    std::int64_t version,
+                                    const std::string& domain,
+                                    Operator fn);
+            OperatorSet _get_operator_set(std::int64_t version, const std::string& domain);
         };
 
     } // namespace onnx_import

test/onnx_import.cpp

@@ -1297,3 +1297,39 @@ TEST(onnx, model_unsupported_op)
         FAIL() << "Expected ngraph::ngraph_error";
     }
 }
+
+TEST(onnx, model_custom_op)
+{
+    onnx_import::register_operator(
+        "AddQ", 1, "com.intel.ai", [](const onnx_import::Node& node) -> NodeVector {
+            NodeVector ng_inputs{node.get_ng_inputs()};
+            return {std::make_shared<ngraph::op::Add>(ng_inputs.at(0), ng_inputs.at(1))};
+        });
+
+    auto function = onnx_import::import_onnx_function(
+        file_util::path_join(SERIALIZED_ZOO, "onnx/custom_operator.onnx"));
+
+    Inputs inputs{{1, 2, 3, 4}};
+    Outputs expected_outputs{{3, 6, 9, 12}};
+
+    Outputs outputs{execute(function, inputs, "INTERPRETER")};
+    EXPECT_TRUE(test::all_close_f(expected_outputs.front(), outputs.front()));
+}
+
+TEST(onnx, model_custom_op_default_domain)
+{
+    onnx_import::register_operator(
+        "AddQ", 1, "com.intel.ai", [](const onnx_import::Node& node) -> NodeVector {
+            NodeVector ng_inputs{node.get_ng_inputs()};
+            return {std::make_shared<ngraph::op::Add>(ng_inputs.at(0), ng_inputs.at(1))};
+        });
+
+    auto function = onnx_import::import_onnx_function(
+        file_util::path_join(SERIALIZED_ZOO, "onnx/custom_operator_default_domain.onnx"));
+
+    Inputs inputs{{1, 2, 3, 4}};
+    Outputs expected_outputs{{3, 6, 9, 12}};
+
+    Outputs outputs{execute(function, inputs, "INTERPRETER")};
+    EXPECT_TRUE(test::all_close_f(expected_outputs.front(), outputs.front()));
+}