What does a three-tier client-server application architecture model include?

In a three-tier client-server application architecture, the model is divided into three distinct layers: the presentation tier, the application tier (or logic tier), and the data tier. The application layer is responsible for processing business logic and querying the data layer to retrieve or manipulate data as necessary. This means that it acts as an intermediary that handles requests from the presentation layer and communicates with the data tier to perform actions like querying databases or processing data.

This architecture allows for better separation of concerns, where each layer can be developed and maintained independently. By having this structured approach, developers can enhance the application more easily, scale it more effectively, and ensure that each layer can evolve without impacting the others directly.

The other options do not encompass the complete structure of a three-tier model. For instance, a single layer for client interactions does not represent the multi-layered nature of the architecture. Similarly, a data tier and a presentation tier alone would miss the crucial application layer that manages the interaction between the two. Direct communication between client and data tier ignores the application's role in processing requests and managing data queries, which is essential for functionality and security in a structured application.