Explanation/Reference:
The Data Normalization Layer provides a standardized format for data entities. Each EIS stores data in its own (usually proprietary) format. This layer transforms the data to a form that is readily consumable by the upper layers in the architecture.
The primary purpose of this layer in the architecture is to encapsulate and hide the complexity of the data models and formats used by the back-end systems. This allows the upper layers in the architecture to operate on data entities that match the needs of the business rather than operating on data that match the storage approach of the back-end systems.
Incorrect answers:
B: Third normal form relates to relation databases only.
C: Not only XML is used.
Reference: Oracle Reference Architecture, Service-Oriented Integration, Release 3.0