wesm commented on a change in pull request #7030:
URL: https://github.com/apache/arrow/pull/7030#discussion_r416638207



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File path: cpp/src/jni/dataset/proto/Types.proto
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@@ -0,0 +1,149 @@
+// 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.
+
+syntax = "proto2";
+package types;
+
+option java_package = "org.apache.arrow.dataset";

Review comment:
       > As for filter, If I understand correctly it's OK to keep Java API but 
the JNI mapping for filters is considered fragile, right? I can remove the 
mapping anyway but when users read parquet files from Java they'll not be able 
to filter row groups to reduce I/O. Which is extremely important when 
low-selectivity filter is specified.
   
   I'm advising you to define some kind of abstraction layer so that the 
_details_ of the C++ API are not exposed in the Java API. So if there are 
changes in the C++ API, then refactoring can take place only at the JNI C++ 
code and no changes will be required in Java. 




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