Creating ONNX Protobuf

In this short tutorial, we’ll make use of the following functions for the examples:

make_xxx() to make different types of protobufs for attributes, nodes, graphs, etc.
check() method that can check whether a protobuf in a particular type is valid.
print_readable() method that can print out the human-readable representation of the proto object.

For detailed definitions of each type of ONNX protobufs, please checkout ONNX intermediate representation spec. A list of available operators, e.g. FC or Relu used in the following examples to define the nodes, can be found here.

Create Node Protobuf

Define a node protobuf and check whether it’s valid:

library(onnx)

node_def <- make_node("Relu", list("X"), list("Y"))
check(node_def)

> node_def
input: "X"
output: "Y"
op_type: "Relu"

Create Attribute Protobuf

Define an attribute protobuf and check whether it’s valid:

attr_def <- make_attribute("this_is_an_int", 123L)
check(attr_def)

> attr_def
name: "this_is_an_int"
i: 123
type: INT

Create Graph Protobuf

Define a graph protobuf and check whether it’s valid:

graph_def <- make_graph(
  nodes = list(
    make_node("FC", list("X", "W1", "B1"), list("H1")),
    make_node("Relu", list("H1"), list("R1")),
    make_node("FC", list("R1", "W2", "B2"), list("Y"))
  ),
  name = "MLP",
  inputs = list(
    make_tensor_value_info('X' , onnx$TensorProto$FLOAT, list(1L)),
    make_tensor_value_info('W1', onnx$TensorProto$FLOAT, list(1L)),
    make_tensor_value_info('B1', onnx$TensorProto$FLOAT, list(1L)),
    make_tensor_value_info('W2', onnx$TensorProto$FLOAT, list(1L)),
    make_tensor_value_info('B2', onnx$TensorProto$FLOAT, list(1L))
  ),
  outputs = list(
    make_tensor_value_info('Y', onnx$TensorProto$FLOAT, list(1L))
  )
)
check(graph_def)

You can use print_readable() to print out the human-readable representation of the graph definition:

> print_readable(graph_def)
graph MLP (
  %X[FLOAT, 1]
  %W1[FLOAT, 1]
  %B1[FLOAT, 1]
  %W2[FLOAT, 1]
  %B2[FLOAT, 1]
) {
  %H1 = FC(%X, %W1, %B1)
  %R1 = Relu(%H1)
  %Y = FC(%R1, %W2, %B2)
  return %Y
}

Or simply print it out to see the detailed graph definition containing nodes, inputs, and outputs:

> graph_def
node {
  input: "X"
  input: "W1"
  input: "B1"
  output: "H1"
  op_type: "FC"
}
node {
  input: "H1"
  output: "R1"
  op_type: "Relu"
}
node {
  input: "R1"
  input: "W2"
  input: "B2"
  output: "Y"
  op_type: "FC"
}
name: "MLP"
input {
  name: "X"
  type {
    tensor_type {
      elem_type: FLOAT
      shape {
        dim {
          dim_value: 1
        }
      }
    }
  }
}
input {
  name: "W1"
  type {
    tensor_type {
      elem_type: FLOAT
      shape {
        dim {
          dim_value: 1
        }
      }
    }
  }
}
input {
  name: "B1"
  type {
    tensor_type {
      elem_type: FLOAT
      shape {
        dim {
          dim_value: 1
        }
      }
    }
  }
}
input {
  name: "W2"
  type {
    tensor_type {
      elem_type: FLOAT
      shape {
        dim {
          dim_value: 1
        }
      }
    }
  }
}
input {
  name: "B2"
  type {
    tensor_type {
      elem_type: FLOAT
      shape {
        dim {
          dim_value: 1
        }
      }
    }
  }
}
output {
  name: "Y"
  type {
    tensor_type {
      elem_type: FLOAT
      shape {
        dim {
          dim_value: 1
        }
      }
    }
  }
}