[GitHub] [iceberg] rymurr commented on a change in pull request #2304: SupportsBranches interface and initial impl w/ Nessie

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rymurr commented on a change in pull request #2304:
URL: https://github.com/apache/iceberg/pull/2304#discussion_r589536025



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File path: api/src/main/java/org/apache/iceberg/catalog/Reference.java
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@@ -0,0 +1,121 @@
+/*
+ * 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.iceberg.catalog;
+
+/**
+ * Reference used for SupportsNamespace.
+ *
+ * <p>A reference can be one of three things:
+ * <ul>
+ *   <li>Branch - a pointer to a commit hash that can be modified</li>
+ *   <li>Tag - a pointer to a commit hash that can't be modified</li>
+ *   <li>Hash - a specific commit hash</li>
+ * </ul>
+ *
+ * <p>A reference is either a Hash or a pointer to a hash. A hash is a specific point in the history of a branching
+ * catalog's history. A reference has two components: a name and a hash. The name is the human readable name that points
+ * to a specific hash.
+ *
+ * <p>A Tag cannot be updated or modified. It can be reassigned to another hash only. A hash can't be changed at all. It
+ * is an immutable identifier to a specific point in the branching catalog's history. A branch can be modified, any
+ * catalog which plans to write or modify iceberg tables should set its reference to a branch.
+ */
+public interface Reference {

Review comment:
       Not sure if this is how we want to do this interface/concrete classes. Not sure what the typical way to do this in iceberg is. In Nessie we use the Immutables library




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