diff --git a/models/book.py b/models/book.py
index f790588..5163d00 100644
--- a/models/book.py
+++ b/models/book.py
@@ -14,7 +14,9 @@ class Book(Base):
     publication_year = Column(Integer)
     author_id = Column(String, ForeignKey("authors.id"), nullable=False)
     
+    # Relationships
     author = relationship("Author", back_populates="books")
     
+    # Timestamps
     created_at = Column(DateTime, default=func.now())
     updated_at = Column(DateTime, default=func.now(), onupdate=func.now())
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