content: /*
   * 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.calcite.schema;
  
  /**
   * An interface to represent a version ID that can be used to create a
   * read-consistent view of a Schema. This interface assumes a strict
   * partial ordering contract that is:
   * <ol>
   * <li>irreflexive: !a.isBefore(a), which means a cannot happen before itself;
   * <li>transitive: if a.isBefore(b) and b.isBefore(c) then a.isBefore(c);
   * <li>antisymmetric: if a.isBefore(b) then !b.isBefore(a).
   * </ol>
   * Implementation classes of this interface must also override equals(Object),
   * hashCode() and toString().
   *
   * @see Schema#snapshot(SchemaVersion)
   */
  public interface SchemaVersion {
  
    /**
     * Returns if this Version happens before the other Version.
     *
     * @param other the other Version object
     */
    boolean isBefore(SchemaVersion other);
  }
  