Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3406#discussion_r104167970
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/catalog/ExternalCatalog.scala
---
@@ -0,0 +1,108 @@
+/*
+ * 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.table.catalog
+
+/**
+ * This class is responsible for interact with external catalog.
+ * Its main responsibilities including:
+ * <ul>
+ * <li> create/drop/alter database or tables for DDL operations
+ * <li> provide tables for calcite catalog, it looks up databases or
tables in the external catalog
+ * </ul>
+ */
+trait ExternalCatalog {
+
+ /**
+ * Adds table into external Catalog
+ *
+ * @param table description of table which to create
+ * @param ignoreIfExists whether to ignore operation if table already
exists
+ */
+ def createTable(table: ExternalCatalogTable, ignoreIfExists: Boolean):
Unit
+
+ /**
+ * Deletes table from external Catalog
+ *
+ * @param dbName database name
+ * @param tableName table name
+ * @param ignoreIfNotExists whether to ignore operation if table not
exist yet
+ */
+ def dropTable(dbName: String, tableName: String, ignoreIfNotExists:
Boolean): Unit
+
+ /**
+ * Alters existed table into external Catalog
+ *
+ * @param table description of table which to alter
+ */
+ def alterTable(table: ExternalCatalogTable): Unit
+
+ /**
+ * Gets table from external Catalog
+ *
+ * @param dbName database name
+ * @param tableName table name
+ * @return table
+ */
+ def getTable(dbName: String, tableName: String): ExternalCatalogTable
+
+ /**
+ * Gets the table name lists from current external Catalog
+ *
+ * @param dbName database name
+ * @return lists of table name
+ */
+ def listTables(dbName: String): Seq[String]
--- End diff --
Java `List` or `Set` instead of `Seq`?
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