In many architectures, such as the three- and four-tier architectures (Figures 1 and 2), t...

In many architectures, such as the three- and four-tier architectures (Figures 1 and 2), the storage of persistent objects is handled by a dedicated layer. In your opinion, which design goals have lead to this decision?

Figure 1 Three-tier architectural style (UML component diagram). Objects are organized into three layers realizing the user interface, the processing, and the storage.

Figure 2 Four-tier architectural style (UML component diagram). The Interface layer of the threetier style is split into two layers to enable more variability on the user interface style.