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/**
 * A factory to instantiate key/value extractors
 */
public interface KeyValueExtractorFactory {
    KeyValueExtractor getKeyValueExtractor(Config config);
}

/**
 * A key/value extractor that extracts key and value from in incoming
 * message envelop
 */
public interface KeyValueExtractor {
    Object getKey(IncomingMessageEnvelop input);
    Object getValue(IncomingMessageEnvelop input);
}

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For bounded datasets delivered (such as files) as streams, the adjunct data store may need to maintain multiple versions of underlying stores in order to guarantee serving of a consistent version. This would require the abstraction of adjunct data store, which manages internally versions of underlying stores.

Key

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and value

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extractor

Another option considered is to embed key extraction and value conversion logic in serde layer. It would work, but would make serde asymmetric and less portable.

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