[FLINK-12473][ml] Add ML pipeline and MLlib interface

This closes apache#8402

flink-ml-parent/flink-ml-api/pom.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+		 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+
+	<parent>
+		<groupId>org.apache.flink</groupId>
+		<artifactId>flink-ml-parent</artifactId>
+		<version>1.9-SNAPSHOT</version>
+	</parent>
+
+	<artifactId>flink-ml-api</artifactId>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.apache.flink</groupId>
+			<artifactId>flink-table-api-java</artifactId>
+			<version>${project.version}</version>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.flink</groupId>
+			<artifactId>flink-shaded-jackson</artifactId>
+			<version>${jackson.version}-${flink.shaded.version}</version>
+		</dependency>
+	</dependencies>
+</project>

flink-ml-parent/flink-ml-api/src/main/java/org/apache/flink/ml/api/core/Estimator.java

@@ -0,0 +1,47 @@
+/*
+ * 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.table.api.Table;
+import org.apache.flink.table.api.TableEnvironment;
+
+/**
+ * Estimators are {@link PipelineStage}s responsible for training and generating machine learning
+ * models.
+ *
+ * <p>The implementations are expected to take an input table as training samples and generate a
+ * {@link Model} which fits these samples.
+ *
+ * @param <E> class type of the Estimator implementation itself, used by {@link
+ *            org.apache.flink.ml.api.misc.param.WithParams}.
+ * @param <M> class type of the {@link Model} this Estimator produces.
+ */
+@PublicEvolving
+public interface Estimator<E extends Estimator<E, M>, M extends Model<M>> extends PipelineStage<E> {
+
+	/**
+	 * Train and produce a {@link Model} which fits the records in the given {@link Table}.
+	 *
+	 * @param tEnv  the table environment to which the input table is bound.
+	 * @param input the table with records to train the Model.
+	 * @return a model trained to fit on the given Table.
+	 */
+	M fit(TableEnvironment tEnv, Table input);
+}

flink-ml-parent/flink-ml-api/src/main/java/org/apache/flink/ml/api/core/Model.java

@@ -0,0 +1,39 @@
+/*
+ * 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.table.api.Table;
+
+/**
+ * A model is an ordinary {@link Transformer} except how it is created. While ordinary transformers
+ * are defined by specifying the parameters directly, a model is usually generated by an {@link
+ * Estimator} when {@link Estimator#fit(org.apache.flink.table.api.TableEnvironment, Table)} is
+ * invoked.
+ *
+ * <p>We separate Model from {@link Transformer} in order to support potential
+ * model specific logic such as linking a Model to the {@link Estimator} from which the model was
+ * generated.
+ *
+ * @param <M> The class type of the Model implementation itself, used by {@link
+ *            org.apache.flink.ml.api.misc.param.WithParams}
+ */
+@PublicEvolving
+public interface Model<M extends Model<M>> extends Transformer<M> {
+}