[GitHub] [flink] ex00 commented on a change in pull request #8402: [FLINK-12473][ml] Add the interface of ML pipeline and ML lib

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ex00 commented on a change in pull request #8402: [FLINK-12473][ml] Add the interface of ML pipeline and ML lib
URL: https://github.com/apache/flink/pull/8402#discussion_r283130149
 
 

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 File path: flink-ml/flink-ml-api/src/main/java/org/apache/flink/ml/api/core/Pipeline.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.api.core;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.ml.api.misc.param.Params;
+import org.apache.flink.ml.util.persist.MLStageFactory;
+import org.apache.flink.table.api.Table;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonObject;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A pipeline is a linear workflow which chains {@link Estimator}s and {@link Transformer}s to
+ * execute an algorithm.
+ *
+ * <p>A pipeline itself can either act as an Estimator or a Transformer, depending on the stages it
+ * includes. More specifically:
+ * <ul>
+ * <li>
+ * If a Pipeline has an {@link Estimator}, one needs to call {@link Pipeline#fit(Table)} before use
+ * the pipeline as a {@link Transformer}. In this case the Pipeline is an {@link Estimator} and can
+ * produce a Pipeline as a {@link Model}.
+ * </li>
+ * <li>
+ * If a Pipeline has no {@link Estimator}, it is a {@link Transformer} and can be applied to a Table
+ * directly. In this case, {@link Pipeline#fit(Table)} will simply return the pipeline itself.
+ * </li>
+ * </ul>
+ *
+ * <p>In addition, a pipeline can also be used as a {@link PipelineStage} in another pipeline, just
+ * like an ordinary {@link Estimator} or {@link Transformer} as describe above.
+ */
+@PublicEvolving
+public final class Pipeline implements Estimator<Pipeline, Pipeline>, Transformer<Pipeline>,
+	Model<Pipeline> {
+	private static final long serialVersionUID = 1L;
+	private List<PipelineStage> stages;
+	private Params params;
+
+	public Pipeline() {
+		this(new ArrayList<>());
+	}
+
+	public Pipeline(List<PipelineStage> stages) {
+		this.stages = stages;
+		this.params = new Params();
 
 Review comment:
    How will be using `params` in this class? Can we set `params` from arguments?

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