SerDe is short for Serializer/Deserializer. A SerDe allows Hive to read in data from a table, and write it back out to HDFS in any custom format. Anyone can write their own SerDe for their own data formats. See Hive SerDe for an introduction to SerDes.
For JSON files, Amazon has provided a JSON SerDe available at:
s3://elasticmapreduce/samples/hive-ads/libs/jsonserde.jar
Hive uses the Serde interface for IO. The interface handles both serialization and deserialization and also interpreting the results of serialization as individual fields for processing.
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