[4] User Defined Functions () <https://pig.apache.org/docs/r0.9.1/udf.html>
[3] Pig ユーザー定義関数メモ(Hishidama's Apache Pig UDF Memo) () <http://www.ne.jp/asahi/hishidama/home/tech/apache/pig/udf.html>
[1] UDF · hiromasah/charsiu Wiki ( 版) <https://github.com/hiromasah/charsiu/wiki/UDF>
[2] UDF説明概要 · hiromasah/charsiu Wiki () <https://github.com/hiromasah/charsiu/wiki/UDF%E8%AA%AC%E6%98%8E%E6%A6%82%E8%A6%81>