Development of an Apex application starts with mapping the functional specification to operators (smaller functional building blocks), which can then be composed into a DAG to collectively provide the functionality required for the use case.
This involves identifying the data sources, formats, transformations and sinks for the application, and finding matching operators from the Apex library (which will be covered in the next chapter). In most cases, the required connectors will be available from the library that support frequent sources, such as files and Kafka, along with many other external systems that are part of the Apache Big Data ecosystem.
With the comprehensive operator library and set of examples to cover frequently used I/O cases and transformations, it is often possible to assemble a preliminary end-to-end flow that covers a subset of the functionality quickly, before building out the complete business logic in detail.
