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In the case of two-tier architecture, also known as a client-data server, or first-generation client-server, the client device is satisfied with assigning data management to another service. A specific example of this architecture is a management application that runs on a Windows or Linux operating system and accesses a central DataBase Management System (DBMS). This application makes it possible to benefit from the power of calculators deployed in a network in order to provide a user-friendly interface, while ensuring consistency of the data, which are always managed centrally.

A centralized DBMS handles data management and runs frequently on a dedicated server. This server is queried using a query language, usually Structured Query Language (SQL). The conversation between the client and the server can therefore be summarized as the sending of requests and, in response, data matching the requests.

Figure 1.7. Two-tier architecture (client-data server)

NOTE.– The exchange of messages between the client and the server is accomplished via a network by means of a middleware (the network layers and software services promoting conversation between the components of a distributed application).

Table 1.3. Benefits and disadvantages of two-tier architecture

Benefits	Disadvantages
User-friendly interface Centralized dataPowerful architecture for a reduced number of users (< 50)	Fat client: the client supports most application processingApplication updates must be deployed for all clientsLimited number of clients: changes in the number of clients cause a degradation in server performance