Final answer:
In three-tier architecture, the database tier executes queries requested from the application tier, and webserver processes manage user interactions. Application-tier processes can span multiple machines, and the database tier can also be distributed across servers, contrary to the claims in statements a) and d).
Step-by-step explanation:
The correct statements in the context of three-tier architecture are as follows:
- The database tier executes queries that are requested from the application tier.
- The webserver processes manage the interactions with the users.
To elaborate, three-tier architecture is a well-known software design pattern that separates the application into three logical tiers: the presentation tier, the application logic tier, and the database tier. Each tier is responsible for a specific aspect of the application. Statement b) is accurate as the database tier's primary responsibility is to execute queries and manage data persistence, typically in response to requests made by the application tier. Statement c) correctly notes that the webserver processes, as part of the presentation tier, manage the interactions with end-users, serving content, and capturing user inputs to pass to the application layer for processing.
Statement a) is incorrect as the application-tier processes may reside on multiple machines for scalability and fault tolerance purposes, not necessarily on one machine. Similarly, statement d) is not accurate because the database tier can also leverage multiple machines to manage large datasets, enhance performance, and ensure high availability.