public class GraphNode {
    public final Stage<?> stage;
    public final TableId[] estimatorInputs;
    public final TableId[] modelInputsalgoOpInputs;
    public final TableId[] outputs;
}

/**
 * A Graph acts as an Estimator. A Graph consists of a DAG of stages, each of which could be an
 * Estimator, Model, Transformer or AlgoOperator. When `Graph::fit` is called, the stages are
 * executed in a topologically-sorted order. If a stage is an Estimator, its `Estimator::fit` method
 * will be called on the input tables (from the input edges) to fit a Model. Then the Model will be
 * used to transform the input tables and produce output tables to the output edges. If a stage is
 * an AlgoOperator, its `AlgoOperator::transform` method will be called on the input tables and
 * produce output tables to the output edges. The GraphModel fitted from a Graph consists of the
 * fitted Models and AlgoOperators, corresponding to the Graph's stages.
 */
@PublicEvolving
public final class Graph implements Estimator<Graph, GraphModel> {
    public Graph(List<GraphNode> nodes, TableId[] estimatorInputIds, TableId[] modelInputsalgoOpInputs, TableId[] outputs, TableId[] inputModelData, TableId[] outputModelData) {...}

    @Override
    public GraphModel fit(Table... inputs) {...}

    @Override
    public void save(String path) throws IOException {...}

    @Override
    public static Graph load(StreamTableEnvironment tEnv, String path) throws IOException {...}
}

/**
 * A GraphModel acts as a Model. A GraphModel consists of a DAG of stages, each of which could be an
 * Estimator, Model, Transformer or AlgoOperators. When `GraphModel::transform` is called, the
 * stages are executed in a topologically-sorted order. When a stage is executed, its
 * `AlgoOperator::transform` method will be called on the input tables (from the input edges) and
 * produce output tables to the output edges.
 */
public final class GraphModel implements Model<GraphModel> {

    public GraphModel(List<GraphNode> nodes, TableId[] inputIds, TableId[] outputIds, TableId[] inputModelData, TableId[] outputModelData) {...}

    @Override
    public Table[] transform(Table... inputTables) {...}

    @Override
    public void setModelData(Table... inputs) {...}

    @Override
    public Table[] getModelData() {...}

    @Override
    public void save(String path) throws IOException {...}

    public static GraphModel load(StreamTableEnvironment tEnv, String path) throws IOException {...}
}

/**
 * A GraphBuilder provides APIs to build Estimator/Model/AlgoOperator from a DAG of stages, each of
 * which could be an Estimator, Model, Transformer or AlgoOperator.
 */
@PublicEvolving
public final class GraphBuilder {
    private int maxOutputLength = 20;

    public GraphBuilder() {}

    /**
     * Specifies the loose upper bound (could be loose) of the number of output tables that can be
 returned by the
  * returned by the* TransformerModel::getModelData() and AlgoOperator::transform() methods, for any stage
 involved in this
  * involved in this* Graph.
     *
     * <p>The default upper bound is 20.
     */
    public GraphBuilder setMaxOutputLengthsetMaxOutputTableNum(int maxOutputLength) {...}

    /**
     * Creates a TableId associated with this GraphBuilder. It can be used to specify the passing of
     * tables between stages, as well as the input/output tables of the Graph/GraphModel generated
     * by this builder.
     *
     * @return A TableId.
     */
    public TableId createTableId() {...}

    /**
     * IfAdds the stage is an Estimator, both its fit method andan AlgoOperator in the graph.
     *
     * <p>When the graph runs as Estimator, the transform() method of itsthe fitted
given AlgoOperator would be
  * Model would be* invoked with the given inputs. Then when the graphGraphModel runs.
fitted by this graph runs, *the
     * <p>Iftransform() thisof stagethe isgiven aAlgoOperator Model,would Transformerbe orinvoked AlgoOperator,with itsthe transform method would begiven inputs.
     *
 invoked with the given inputs* when<p>When the graph runs.
 as AlgoOperator or Model, *
the transform() of the given *AlgoOperator
 <p>Returns a list of TableIds,* whichwould representsbe outputsinvoked of AlgoOperator::transform of with the given stageinputs.
     */
    public TableId[] getOutputs(Stage<?> stage, TableId... inputs) {...}

    /**
     * If this stage is an Estimator, its fit method would be invoked with estimatorInputs, and the* <p>NOTE: the number of the returned TableIds does not represent the actual number of Tables
     * outputted by transform(). This number could be configured using {@link
     * transform method of its fitted Model would be invoked with modelInputs.#setMaxOutputTableNum(int)}. Users should make sure that this number >= the actual number of
     *
 Tables outputted by transform().
     *
 <p>This method throws Exception if* the@param stagealgoOp isAn notAlgoOperator an Estimatorinstance.
     *
 @param inputs A list of TableIds *which <p>Thisrepresents methodinputs isto usefultransform() whenof the stategiven
  is an Estimator AND* the Estimator::fit needs to takeAlgoOperator.
     * a@return differentA list of TablesTableIds which fromrepresents the Model::transformoutputs of transform() of the fitted Model.given
     *
     * <p>Returns a list of TableIds, which represents outputs of Model::transform of the fitted ModelAlgoOperator.
     */
    public TableId[] getOutputsaddAlgoOperator(Stage<AlgoOperator<?> stagealgoOp, TableId[] estimatorInputs, TableId[] modelInputs... inputs) {...}

    /**
     * The setModelData() of the fitted GraphModel should invoke the setModelDataAdds an Estimator in the graph.
     *
     * <p>When the graph runs as Estimator, the fit() of the given Estimator would be invoked with
     * stage with the given inputs.
 Then when the GraphModel */
fitted by this graph publicruns, voidthe setModelDatatransform(Stage<?> stage, TableId... inputs) {...}

) of the
     * /**
Model     * The getModelData() of the fitted GraphModel should invoke the getModelData() offitted by the given Estimator would be invoked with the given inputs.
     * stage.
     *
 <p>When the graph runs *as <p>ReturnsAlgoOperator a list of TableIds, which represents the outputs of getModelDataor Model, the fit() of the given
 Estimator    * stage.would be
     */
 invoked with the given public TableId[] getModelData(Stage<?> stage) {...}

    /**inputs, then the transform() of the Model fitted by the given
     * ReturnsEstimator anwould Estimatorbe instanceinvoked with the followinggiven behavior:inputs.
     *
     * <p>1) Estimator::fit should take<p>NOTE: the number of the givenreturned inputsTableIds anddoes returnnot a Modelrepresent with the following
actual number    * behavior.of Tables
     *
 outputted by transform(). This *number <p>2) Model::transform should take the given inputs and return the given outputs.
     *
     * <p>The fit method of the returned Estimator and the transform method of the fitted Modelcould be configured using {@link
     * #setMaxOutputTableNum(int)}. Users should make sure that this number >= the actual number of
     * Tables outputted by transform().
     *
     * should@param invokeestimator theAn correspondingEstimator methodsinstance.
 of the internal stages as* specified@param byinputs the
A list of TableIds which *represents GraphBuilder.
inputs to fit() of the */
given Estimator as
  public Estimator<?, ?> buildEstimator(TableId[] inputs, TableId[] outputs) {...}

    /**
     * Returns an Estimator instance with the following behavior:
     *
     * <p>1) Estimator::fit should take the given inputs and returns a Model with the following
     * behavior *     well as inputs to transform() of the Model fitted by the given Estimator.
     * @return A list of TableIds which represents the outputs of transform() of the Model fitted by
     *     the given Estimator.
     */
    public * <p>2) Model::transform should take the given inputs and return the given outputs.
TableId[] addEstimator(Estimator<?, ?> estimator, TableId... inputs) {...}

     /**
     * <p>3) Model::setModelData should takeAdds an Estimator in the given inputModelDatagraph.
     *
     * <p>4) Model::getModelData should return<p>When the graph runs as Estimator, the fit() of the given outputModelData.
Estimator would be invoked  *with
     * <p>TheestimatorInputs. fitThen methodwhen of the returnedGraphModel Estimatorfitted and by this graph runs, the transform/setModelData/getModelData() of the
     * methodsModel fitted ofby the fittedgiven ModelEstimator shouldwould invokebe theinvoked correspondingwith methodsmodelInputs.
 of the internal stages as*
     * specified by the GraphBuilder.
     */ <p>When the graph runs as AlgoOperator or Model, the fit() of the given Estimator would be
    public Estimator<?, ?> buildEstimator(TableId[] inputs, TableId[] outputs, TableId[] inputModelData, TableId[] outputModelData) {...}

    /*** invoked with estimatorInputs, then the transform() of the Model fitted by the given Estimator
     * Returnswould anbe Estimatorinvoked instance with the following behavior:modelInputs.
     *
     * <p>1) Estimator::fit should take<p>NOTE: the number of the givenreturned estimatorInputsTableIds anddoes returnsnot arepresent Modelthe with theactual number of Tables
     * following behavior.
     *outputted by transform(). This number could be configured using {@link
     * <p>2#setMaxOutputTableNum(int) Model::transform}. Users should takemake thesure giventhat transformerInputsthis andnumber return>= the given outputs.actual number of
     *
 Tables outputted   * <p>3) Model::setModelData should take the given inputModelDataby transform().
     *
     * @param *estimator <p>4) Model::getModelData should return the given outputModelDataAn Estimator instance.
     *
 @param estimatorInputs A list *of <p>TheTableIds fitwhich methodrepresents ofinputs theto returnedfit() Estimatorof and the transform/setModelData/getModelDatagiven
     * methods of the fitted ModelEstimator.
 should invoke the corresponding methods* of@param themodelInputs internalA stageslist as
of TableIds which represents inputs *to specifiedtransform() byof the GraphBuilder.Model
     */     fitted by the given Estimator.
    public Estimator<?, ?> buildEstimator(TableId[] estimatorInputs, TableId[] modelInputs, TableId[] outputs, TableId[] inputModelData, TableId[] outputModelData) {...}

    /*** @return A list of TableIds which represents the outputs of transform() of the Model fitted by
     * Returns an AlgoOperator instance with the followinggiven behavior:Estimator.
     */
    public * <p>1) AlgoOperator::transform should take the given inputs and returns the given outputs.
     *
     * <p>The transform method of the returned AlgoOperator should invoke the corresponding methods
     * of the internal stages as specified by the GraphBuilder.TableId[] addEstimator(
            Estimator<?, ?> estimator, TableId[] estimatorInputs, TableId[] modelInputs) {...}

    /**
     * When the graph runs as Estimator, it first generates a GraphModel that contains the Model
     * fitted by the given Estimator. Then when this GraphModel runs, the setModelData() of the
     */
 fitted Model would be public AlgoOperator<?> buildAlgoOperator(TableId[] inputs, TableId[] outputs) {...}

invoked with the given inputs before its transform() is invoked.
     /**
     * Returns a Model instance with the following behavior:<p>When the graph runs as AlgoOperator or Model, the setModelData() of the Model fitted by
     * the given Estimator would be invoked with the given inputs before its transform() is invoked.
     *
     * @param estimator An Estimator instance.
     * @param inputs A list of TableIds which represents inputs to setModelData() of the Model
     *     fitted by the given Estimator.
     */
    public void setModelDataOnEstimator(Estimator<?, ?> estimator, TableId... inputs) {...}

    /**
     * When the graph runs as Estimator, the setModelData() of the given Model would be invoked with
     * the given inputs before its transform() is invoked. Then when the GraphModel fitted by this
     * graph runs, the setModelData() of the given Model would be invoked with the given inputs.
     *
     * <p>When the graph runs as AlgoOperator or Model, the setModelData() of the given Model would
     * be invoked with the given inputs before its transform() is invoked.
     *
     * @param model A Model instance.
     * @param inputs A list of TableIds which represents inputs to setModelData() of the given
     *     Model.
     */
    public void setModelDataOnModel(Model<?> model, TableId... inputs) {...}

    /**
     * When the graph runs as Estimator, it first generates a GraphModel that contains the Model
     * fitted by the given Estimator. Then when this GraphModel runs, the getModelData() of the
     * fitted Model would be invoked.
     *
     * <p>When the graph runs as AlgoOperator or Model, the getModelData() of the Model fitted by
     * the given Estimator would be invoked.
     *
     * <p>NOTE: the number of the returned TableIds does not represent the actual number of Tables
     * outputted by getModelData(). This number could be configured using {@link
     * #setMaxOutputTableNum(int)}. Users should make sure that this number >= the actual number of
     * Tables outputted by getModelData().
     *
     * @param estimator An Estimator instance.
     * @return A list of TableIds which represents the outputs of getModelData() of the Model fitted
     *     by the given Estimator.
     */
    public TableId[] getModelDataFromEstimator(Estimator<?, ?> estimator) {...}

    /**
     * When the graph runs as Estimator, the getModelData() of the given Model would be invoked.
     * Then when the GraphModel fitted by this graph runs, the getModelData() of the given Model
     * would be invoked.
     *
     * <p>When the graph runs as AlgoOperator or Model, the getModelData() of the given Model would
     * be invoked.
     *
     * <p>NOTE: the number of the returned TableIds does not represent the actual number of Tables
     * outputted by getModelData(). This number could be configured using {@link
     * #setMaxOutputTableNum(int)}. Users should make sure that this number >= the actual number of
     * Tables outputted by getModelData().
     *
     * @param model A Model instance.
     * @return A list of TableIds which represents the outputs of getModelData() of the given Model.
     */
    public TableId[] getModelDataFromModel(Model<?> model) {...}

    /**
     * Wraps nodes of the graph into an Estimator.
     *
     * <p>When the returned Estimator runs, and when the Model fitted by the returned Estimator
     * runs, the sequence of operations recorded by the {@code addAlgoOperator(...)}, {@code
     * addEstimator(...)}, {@code setModelData(...)} and {@code getModelData(...)} would be executed
     * as specified in the Java doc of the corresponding methods.
     *
     * @param inputs A list of TableIds which represents inputs to fit() of the returned Estimator
     *     as well as inputs to transform() of the Model fitted by the returned Estimator.
     * @param outputs A list of TableIds which represents outputs of transform() of the Model fitted
     *     by the returned Estimator.
     * @return An Estimator which wraps the nodes of this graph.
     */
    public Estimator<?, ?> buildEstimator(TableId[] inputs, TableId[] outputs) {...}

    /**
     * Wraps nodes of the graph into an Estimator.
     *
     * <p>When the returned Estimator runs, and when the Model fitted by the returned Estimator
     * runs, the sequence of operations recorded by the {@code addAlgoOperator(...)}, {@code
     * addEstimator(...)}, {@code setModelData(...)} and {@code getModelData(...)} would be executed
     * as specified in the Java doc of the corresponding methods.
     *
     * @param inputs A list of TableIds which represents inputs to fit() of the returned Estimator
     *     as well as inputs to transform() of the Model fitted by the returned Estimator.
     * @param outputs A list of TableIds which represents outputs of transform() of the Model fitted
     *     by the returned Estimator.
     * @param inputModelData A list of TableIds which represents inputs to setModelData() of the
     *     Model fitted by the returned Estimator.
     * @param outputModelData A list of TableIds which represents outputs of getModelData() of the
     *     Model fitted by the returned Estimator.
     * @return An Estimator which wraps the nodes of this graph.
     */
    public Estimator<?, ?> buildEstimator(
            TableId[] inputs,
            TableId[] outputs,
            TableId[] inputModelData,
            TableId[] outputModelData) {...}

    /**
     * Wraps nodes of the graph into an Estimator.
     *
     * <p>When the returned Estimator runs, and when the Model fitted by the returned Estimator
     * runs, the sequence of operations recorded by the {@code addAlgoOperator(...)}, {@code
     * addEstimator(...)}, {@code setModelData(...)} and {@code getModelData(...)} would be executed
     * as specified in the Java doc of the corresponding methods.
     *
     * @param estimatorInputs A list of TableIds which represents inputs to fit() of the returned
     *     Estimator.
     * @param modelInputs A list of TableIds which represents inputs to transform() of the Model
     *     fitted by the returned Estimator.
     * @param outputs A list of TableIds which represents outputs of transform() of the Model fitted
     *     by the returned Estimator.
     * @param inputModelData A list of TableIds which represents inputs to setModelData() of the
     *     Model fitted by the returned Estimator.
     * @param outputModelData A list of TableIds which represents outputs of getModelData() of the
     *     Model fitted by the returned Estimator.
     * @return An Estimator which wraps the nodes of this graph.
     */
    public Estimator<?, ?> buildEstimator(
            TableId[] estimatorInputs,
            TableId[] modelInputs,
            TableId[] outputs,
            TableId[] inputModelData,
            TableId[] outputModelData) {...}

    /**
     * Wraps nodes of the graph into an AlgoOperator.
     *
     * <p>When the returned AlgoOperator runs, the sequence of operations recorded by the {@code
     * addAlgoOperator(...)} and {@code addEstimator(...)} would be executed as specified in the
     * Java doc of the corresponding methods.
     *
     * @param inputs A list of TableIds which represents inputs to transform() of the returned
     *     AlgoOperator.
     * @param outputs A list of TableIds which represents outputs of transform() of the returned
     *     AlgoOperator.
     * @return An AlgoOperator which wraps the nodes of this graph.
     */
    public AlgoOperator<?> buildAlgoOperator(TableId[] inputs, TableId[] outputs) {...}

    /**
     * Wraps nodes of the graph into a Model.
     *
     * <p>When the returned Model runs, the sequence of operations recorded by the {@code
     * addAlgoOperator(...)} and {@code addEstimator(...)} would be executed as specified in the
     * Java doc of the corresponding methods.
     *
     * @param inputs A list of TableIds which represents inputs to transform() of the returned
     *     Model.
     * @param outputs A list of TableIds which represents outputs of transform() of the returned
     *     Model.
     * @return A Model which wraps the nodes of this graph.
     */
    public Model<?> buildModel(TableId[] inputs, TableId[] outputs) {...}

    /**
     * Wraps nodes of the graph into a Model.
     *
     * <p>When the returned Model runs, the sequence of operations recorded by the {@code
     * addAlgoOperator(...)}, {@code addEstimator(...)}, {@code setModelData(...)} and {@code
     *
 getModelData(...)} would be executed *as <p>1) Model::transform should takespecified in the givenJava inputsdoc and returnsof the given outputs.corresponding
     * methods.
     *
 <p>The transform method of the* returned@param Modelinputs should invoke the corresponding methods of the
     * internal stages as specified by the GraphBuilder.
     */A list of TableIds which represents inputs to transform() of the returned
    public Model<?> buildModel(TableId[] inputs, TableId[] outputs) {...}

*     Model.
     /**
     * Returns a Model instance with the following behavior:* @param outputs A list of TableIds which represents outputs of transform() of the returned
     *
     * <p>1) Model::transform should take the given inputs and returns the given outputs.
     *Model.
     * @param inputModelData A list of TableIds which represents inputs to setModelData() of the
     * <p>2) Model::setModelData should take the givenreturned inputModelDataModel.
     *
 @param outputModelData A list *of <p>3) Model::getModelData should return the given outputModelData.
     *TableIds which represents outputs of getModelData() of the
     * <p>The transform/setModelData/getModelData methods of the returned Model should invoke the.
     * corresponding methods@return ofA theModel internalwhich stageswraps asthe specifiednodes byof thethis GraphBuildergraph.
     */
    public Model<?> buildModel(
            TableId[] inputs,
            TableId[] outputs,
            TableId[] inputModelData,
            TableId[] outputModelData) {...}
}

GraphBuilder builder = new GraphBuilder();

// Creates nodes
Stage<AlgoOperator<?> stage1 = new TransformerA();
Stage<AlgoOperator<?> stage2 = new TransformerA();
Stage<Estimator<?> stage3 = new EstimatorB();
// Creates inputs and inputStates
TableId input1 = builder.createTableId();
TableId input2 = builder.createTableId();
// Feeds inputs to nodes and gets outputs.
TableId output1 = builder.getOutputsaddAlgoOperator(stage1, input1)[0];
TableId output2 = builder.getOutputsaddAlgoOperator(stage2, input2)[0];
TableId output3 = builder.getOutputsaddEstimator(stage3, output1, output2)[0];

// Specifies the ordered lists of inputs, outputs, input states and output states that will
// be used as the inputs/outputs of the corresponding Graph and GraphTransformer APIs.
TableId[] inputs = new TableId[] {input1, input2};
TableId[] outputs = new TableId[] {output3};

// Generates the Graph instance.
Estimator<?, ?> estimator = builder.buildEstimator(inputs, outputs);
// The fit method takes 2 tables which are mapped to input1 and input2.
Model<?> model = estimator.fit(...);
// The transform method takes 2 tables which are mapped to input1 and input2.
Table[] results = model.transform(...);

GraphBuilder builder = new GraphBuilder();

// Creates nodes
Stage<Estimator<?> stage1 = new EstimatorA();
Stage<AlgoOperator<?> stage2 = new TransformerB();
// Creates inputs
TableId estimatorInput1 = builder.createTableId();
TableId estimatorInput2 = builder.createTableId();
TableId transformerInput1 = builder.createTableId();

// Feeds inputs to nodes and gets outputs.
TableId output1 = builder.getOutputsaddEstimator(stage1, new TableId[] {estimatorInput1, estimatorInput2}, new TableId[] {transformerInput1})[0];
TableId output2 = builder.getOutputsaddAlgoOperator(stage2, output1)[0];

// Specifies the ordered lists of estimator inputs, transformer inputs, outputs, input states and output states
// that will be used as the inputs/outputs of the corresponding Graph and GraphTransformer APIs.
TableId[] estimatorInputs = new TableId[] {estimatorInput1, estimatorInput2};
TableId[] transformerInputs = new TableId[] {transformerInput1};
TableId[] outputs = new TableId[] {output2};
TableId[] inputModelData = new TableId[] {};
TableId[] outputModelData = new TableId[] {};

// Generates the Graph instance.
Estimator<?, ?> estimator = builder.buildEstimator(estimatorInputs, transformerInputs, outputs, inputModelData, outputModelData);
// The fit method takes 2 tables which are mapped to estimatorInput1 and estimatorInput2.
Model<?> model = estimator.fit(...);
// The transform method takes 1 table which is mapped to transformerInput1.
Table[] results = model.transform(...);