Complex sentence: The first is the Class Syntax Notation (CSN), a data definition language used to define a dataset's schema; the second is the Object Syntax Notation, a complementary language used to represent the object data adhering to the schema.
Split into simpler sentences: The first is the Class Syntax Notation (CSN), a data definition language used to define a dataset's schema. Th second is the Object Syntax Notation (OSN), a complementary language used to represent the object data adhering to the schema.