Final answer:
The question discusses database architectures, specifically 2-tier and 3-tier models. The 2-tier consists of a client layer and a database server, with a middleware SQL and network layer. The 3-tier model adds an application/web server layer that separates the client from the database server, enhancing the system's organization and capabilities.
Step-by-step explanation:
Client-Server and Three-Tier Architectures
The question appears to concern different types of database architecture, particularly focusing on client-server models and how they vary in complexity and structure. A logical 2-tier architecture consists of a client layer (Layer 1) which interacts directly with the end user and a database server (Layer 2) where the data is stored and managed. Between these layers is a middleware layer, which in this case includes SQL and network protocols to communicate between the client and the server.
The three-tier architecture extends upon this by introducing a middle layer known as the application/web server (Layer 2). This layer contains the business logic and potentially the web server itself. It acts as an intermediary between the client (Layer 1) and the database server (Layer 3), improving structure, security, and scalability.