What is labeled A in this diagram? 
Definitions:
Transaction
The act of buying or selling something; a business deal or financial exchange.
Customer Database
A collection of information about customers, including contact details, purchase history, and preferences, used by businesses to tailor marketing efforts and improve service.
Online Retailer
A business that sells products or services to customers through the internet, without a physical storefront.
Amazon.com
A global online retail platform and technology company that offers a wide range of products and services, including e-commerce, cloud computing, and artificial intelligence.
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