# Entry Points And Helper Classes

Overview

Entry points are a way to interface with ML.NET components, by specifying an execution graph of connected inputs and outputs of those components. Both the manifest describing available components and their inputs/outputs, and an “experiment” graph description, are expressed in JSON. The recommended way of interacting with ML.NET through other, non-.NET programming languages, is by composing, and exchanging pipelines or experiment graphs.

Through the documentation, we also refer to entry points as ‘entry points nodes’, and that is because they are the nodes of the graph representing the experiment. The graph ‘variables’, the various values of the experiment graph JSON properties, serve to describe the relationship between the entry point nodes. The ‘variables’ are therefore the edges of the DAG (Directed Acyclic Graph).

All of ML.NET entry points are described by their manifest. The manifest is another JSON object that documents and describes the structure of an entry points. Manifests are referenced to understand what an entry point does, and how it should be constructed, in a graph.

This document briefly describes the structure of the entry points, the structure of an entry point manifest, and mentions the ML.NET classes that help construct an entry point graph.

EntryPoint manifest - the definition of an entry point

The components manifest is build by scanning the ML.NET assemblies through reflection and searching for types having the: SignatureEntryPointModule signature in their LoadableClass assembly attribute definition. An example of an entry point manifest object, specifically for the ColumnTypeConverter transform, is:

{
    "Name": "Transforms.ColumnTypeConverter",
    "Desc": "Converts a column to a different type, using standard conversions.",
    "FriendlyName": "Convert Transform",
    "ShortName": "Convert",
    "Inputs": [
        {   "Name": "Column",
            "Type": {
                "Kind": "Array",
                "ItemType": {
                    "Kind": "Struct",
                    "Fields": [
                        {
                            "Name": "ResultType",
                            "Type": {
                                "Kind": "Enum",
                                "Values": [ "I1","I2","U2","I4","U4","I8","U8","R4","Num","R8","TX","Text","TXT","BL","Bool","TimeSpan","TS","DT","DateTime","DZ","DateTimeZone","UG","U16" ]
                            },
                            "Desc": "The result type",
                            "Aliases": [ "type" ],
                            "Required": false,
                            "SortOrder": 150,
                            "IsNullable": true,
                            "Default": null
                        },
                        {   "Name": "Range",
                            "Type": "String",
                            "Desc": "For a key column, this defines the range of values",
                            "Aliases": [ "key" ],
                            "Required": false,
                            "SortOrder": 150,
                            "IsNullable": false,
                            "Default": null
                        },
                        {   "Name": "Name",
                            "Type": "String",
                            "Desc": "Name of the new column",
                            "Aliases": [ "name" ],
                            "Required": false,
                            "SortOrder": 150,
                            "IsNullable": false,
                            "Default": null
                        },
                        {   "Name": "Source",
                            "Type": "String",
                            "Desc": "Name of the source column",
                            "Aliases": [ "src" ],
                            "Required": false,
                            "SortOrder": 150,
                            "IsNullable": false,
                            "Default": null
                        }
                    ]
                }
            },
            "Desc": "New column definition(s) (optional form: name:type:src)",
            "Aliases": [ "col" ],
            "Required": true,
            "SortOrder": 1,
            "IsNullable": false
        },
        {   "Name": "Data",
            "Type": "DataView",
            "Desc": "Input dataset",
            "Required": true,
            "SortOrder": 2,
            "IsNullable": false
        },
        {   "Name": "ResultType",
            "Type": {
                "Kind": "Enum",
                "Values": [ "I1","I2","U2","I4","U4","I8","U8","R4","Num","R8","TX","Text","TXT","BL","Bool","TimeSpan","TS","DT","DateTime","DZ","DateTimeZone","UG","U16" ]
            },
            "Desc": "The result type",
            "Aliases": [ "type" ],
            "Required": false,
            "SortOrder": 2,
            "IsNullable": true,
            "Default": null
        },
        {   "Name": "Range",
            "Type": "String",
            "Desc": "For a key column, this defines the range of values",
            "Aliases": [ "key" ],
            "Required": false,
            "SortOrder": 150,
            "IsNullable": false,
            "Default": null
        }
    ],
    "Outputs": [
        {
            "Name": "OutputData",
            "Type": "DataView",
            "Desc": "Transformed dataset" 
        },
        {
            "Name": "Model",
            "Type": "TransformModel",
            "Desc": "Transform model"
        }
    ],
    "InputKind": ["ITransformInput" ],
    "OutputKind": [ "ITransformOutput" ]
}

The respective entry point, constructed based on this manifest would be:

    {
        "Name": "Transforms.ColumnTypeConverter",
        "Inputs": {
            "Column": [{ 
            "Name": "Features",
                    "Source": "Features"
                }],
            "Data": "$data0",
            "ResultType": "R4"
        },
        "Outputs": {
            "OutputData": "$Convert_Output",
            "Model": "$Convert_TransformModel"
        }
    }

EntryPointGraph

This class encapsulates the list of nodes (EntryPointNode) and edges (EntryPointVariable inside a RunContext) of the graph.

EntryPointNode

This class represents a node in the graph, and wraps an entry point call. It has methods for creating and running entry points. It also has a reference to the RunContext to allow it to get and set values from EntryPointVariables.

To express the inputs that are set through variables, a set of dictionaries are used. The InputBindingMap maps an input parameter name to a list of ParameterBindings. The InputMap maps a ParameterBinding to a VariableBinding. For example, if the JSON looks like this:

'foo': '$bar'

the InputBindingMap will have one entry that maps the string “foo” to a list that has only one element, a SimpleParameterBinding with the name “foo” and the InputMap will map the SimpleParameterBinding to a SimpleVariableBinding with the name “bar”. For a more complicated example, let’s say we have this JSON:

'foo': [ '$bar[3]', '$baz']

the InputBindingMap will have one entry that maps the string “foo” to a list that has two elements, an ArrayIndexParameterBinding with the name “foo” and index 0 and another one with index 1. The InputMap will map the first ArrayIndexParameterBinding to an ArrayIndexVariableBinding with name “bar” and index 3 and the second ArrayIndexParameterBinding to a SimpleVariableBinding with the name “baz”.

For outputs, a node assumes that an output is mapped to a variable, so the OutputMap is a simple dictionary from string to string.

EntryPointVariable

This class represents an edge in the entry point graph. It has a name, a type and a value. Variables can be simple, arrays and/or dictionaries. Currently, only data views, file handles, predictor models and transform models are allowed as element types for a variable.

RunContext

This class is just a container for all the variables in a graph.

VariableBinding and Derived Classes

The abstract base class represents a “pointer to a (part of a) variable”. It is used in conjunction with ParameterBindings to specify inputs to an entry point node. The SimpleVariableBinding is a pointer to an entire variable, the ArrayIndexVariableBinding is a pointer to a specific index in an array variable, and the DictionaryKeyVariableBinding is a pointer to a specific key in a dictionary variable.

ParameterBinding and Derived Classes

The abstract base class represents a “pointer to a (part of a) parameter”. It parallels the VariableBinding hierarchy and it is used to specify the inputs to an entry point node. The SimpleParameterBinding is a pointer to a non-array, non-dictionary parameter, the ArrayIndexParameterBinding is a pointer to a specific index of an array parameter and the DictionaryKeyParameterBinding is a pointer to a specific key of a dictionary parameter.

How to create an entry point for an existing ML.NET component

The steps to take, to create an entry point for an existing ML.NET component, are:

  1. Add the SignatureEntryPointModule signature to the LoadableClass assembly attribute.
  2. Create a public static method, that: a. Takes as input, among others, an object representing the arguments of the component you want to expose. b. Initializes and run the components, returning one of the nested classes of Microsoft.ML.Runtime.EntryPoints.CommonOutputs c. Is annotated with the TlcModule.EntryPoint attribute

Based on the type of entry point being created, there are further conventions on the name of the method, for example, the Trainers entry points are typically called: ‘TrainMultiClass’, ‘TrainBinary’ etc, based on the task. Look at OnlineGradientDescent for an example of a component and its entry point.