You are developing an e-commerce application requiring complex transactions and relationships between entities, such as users, orders, and products. What type of database would be most appropriate, and what considerations should you have regarding normalization and indexing?

A relational database would be most appropriate for complex transactions and entity relationships in an e-commerce application. Considerations include normalization to eliminate data redundancy and indexing for efficient querying. Proper indexing strategies can significantly improve query performance in relational databases.