Which of the following is a required attribute in a transformation definition?

In a transformation definition within Splunk, the required attribute is DEST_KEY. This attribute specifies where the result of the transformation should be stored. Essentially, it dictates the output location for the data that has been processed or transformed based on the defined rules. Without this attribute, the transformation would not have a clear destination for the output, which is essential for data manipulation and extraction processes.

In contrast, the other attributes serve different roles. SOURCE_KEY is used to identify the original data source to which the transformation applies, while FORMAT is often utilized to define how the output should be formatted. REGEX is involved in pattern matching and is useful for specifying the conditions of the transformation but is not mandatory. Therefore, DEST_KEY stands out as a necessary component for successful data transformations in the Splunk environment.