Which of the following is a key technical requirement for using ABAP in SAP S/4HANA?

The key technical requirement of enabling database independence in SAP S/4HANA is crucial because it reflects the architecture's design to abstract the underlying database technology. In SAP S/4HANA, the database is optimized to work with the HANA database, which provides high performance for data processing. However, allowing for database independence ensures that ABAP programs can function without being tightly coupled to any specific database system, thereby providing flexibility in deploying across various database backends. This design principle enables developers to write code that is not only efficient but also adaptable to different database technologies, which is essential for future-proofing applications as technology evolves.

The other options do not fulfill a key requirement. Classical database queries may not leverage the advanced capabilities of the HANA database, which can limit performance. Relying solely on procedural programming conflicts with ABAP's flexibility, as the language supports both procedural and object-oriented programming paradigms. Additionally, implementing complex joins always in open SQL might not be necessary, as HANA provides more efficient ways to handle data retrieval through optimized SQL capabilities, reducing the need for manual joins in every situation.