Firm foundation in the main hci principles, the book provides a working

5.4 Summary
In this chapter, we looked at the inner workings of the general under-
lying software structure (UI layer or UI execution framework) on 
which interactive programs operate. Most UI frameworks operate in 
similar ways according to an event-driven structure. The hardware 
input devices generate events that are conveyed to the software inter-
faces (i.e., UI objects), and they are processed to produce output by the 
event-handling codes. The UI layer sitting above the operating system 
(OS) provides the computational framework for such an event-driven 
processing model and makes useful abstractions of the lower OS details 
for easier and intuitive interactive software and interface development. 
The next chapters introduce toolkits and development frameworks that 
make the interface development even more convenient and faster.

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9 3
U S E R I N T E R FA C E L AY E R
Reference
1. Olsen, Dan. 1998. Developing user interfaces: Interactive technologies. San 
Francisco, CA: Morgan Kaufman.

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9 5
6
UI D
E V E LO P M E N T
T
O O L K I T
Now that we have the basic understanding of how the user-interactive 
(UI) software operates with events (most of them predefined and some-
times newly defined by the user), UI objects, and event handlers, the 
next question will be: “What are the programming constructs that allow 
us to specify these for actual implementation of a working interactive 
program?” As was mentioned in the early part of Chapter 4 and as 
illustrated in Figure 5.1, interactive programs and their interfaces are 
often developed using UI development toolkits. To be more precise, 
interfaces are developed using the UI toolkits and the core application 
logics using conventional programming languages. Obviously, the UI 
toolkits are closely related to the UI execution framework (Chapter 5) 
upon which the resulting interactive program would be running.
In the larger scheme of things, we can also think of a UI develop-
ment framework (Chapter 7) as a methodology for the interactive pro-
gram development as a whole. One such example might be a modular 
approach, where the core computational and interface parts are devel-
oped separately and combined in a flexible manner. This allows the 
concept of plugging in different interfaces for the same model com-
putation and thus easier maintenance of the overall program. We first 
take a look at the UI toolkit.