1. A system, comprising: a memory; and a processor coupled to the memory, wherein the processor performs operations, the operations comprising: receiving a first version of an input data schema comprising a first plurality of elements and a second version of the input data schema comprising a second plurality of elements; in response to determining that a user is interested in an output corresponding to selected elements of elements that are present in both the first plurality of elements and the second plurality of elements, and is not interested in outputs corresponding to other elements that are present in the first plurality of elements or the second plurality of elements, performing a selection of the selected elements, wherein the selected elements are common to the first version and the second version of the input data schema but are fewer in number than at least one of the first plurality of elements and the second plurality of elements, based on an expected result corresponding to the selected elements; generating, by an Extract Transform Load (ETL) component, a combined schema from the first version of the input data schema and the second version of the input data schema, wherein the combined schema includes the selected elements and no other elements; in response to generating the combined schema, processing input data according to the combined schema to generate an output by generating and sending streaming events based on the combined schema from a parser to a state machine to validate incoming data and generate the output, wherein the streaming events correspond to tokens generated by the parser from the input data, and the combined schema corresponds to the state machine; and during the processing of the input data according to the combined schema, performing: defining another version of the input data schema, wherein the another version does not affect a structure of elements of interest from the output; and in response to defining the another version of the input data schema, the ETL component continues to execute and still generates the output in accordance with the combined schema.