[4] [CITE[User Defined Functions]] ([TIME[2011-10-06 02:43:26 +09:00]]) <https://pig.apache.org/docs/r0.9.1/udf.html>

[3] [CITE@ja[Pig ユーザー定義関数メモ(Hishidama's Apache Pig UDF Memo)]] ([TIME[2016-11-29 08:13:49 +09:00]]) <http://www.ne.jp/asahi/hishidama/home/tech/apache/pig/udf.html>

[1] [CITE@en[UDF · hiromasah/charsiu Wiki]] ([TIME[2016-10-29 12:55:53 +09:00]] 版) <https://github.com/hiromasah/charsiu/wiki/UDF>

[2] [CITE@en[UDF説明概要 · hiromasah/charsiu Wiki]] ([TIME[2017-05-14 13:44:17 +09:00]]) <https://github.com/hiromasah/charsiu/wiki/UDF%E8%AA%AC%E6%98%8E%E6%A6%82%E8%A6%81>