Chapter 8:

Summary

In this chapter, we discuss the programming support that is provided for the implementation of an interactive system. We have spent much effort up to this point considering design and analysis of interactive systems from a relatively abstract perspective.  

Window systems provide only the crudest level of abstraction for the programmer, allowing her to gain device independence and multiple application control. They do not, however, provide a means of separating the control of presentation and application dialog. We described two paradigms for interactive programming, and saw that these relate to two means of controlling that dialog – either internal to the application by means of a read–evaluation loop or external to the application by means of notification-based programming. Toolkits used with particular windowing systems add another level of abstraction by combining input and output behaviors to provide the programmer with access to interaction objects from which to build the components of the interactive system. Toolkits are amenable to external dialog control by means of callback procedures within the application. Other dialog control techniques are provided with yet another level of abstraction in interactive system development: user interface management systems. UIMS provide a conceptual architecture for dividing up the relationship between application and presentation, and various techniques were described to implement the logical components of a UIMS. An interesting additional means of dialog control can be seen to emerge in the use of graphical specification languages which move dialog control all the way across the spectrum to reside entirely within the presentation language. This presentation control opens up interactive programming to the non-expert programmer, but at the cost of a loss of expressiveness.

A programming tools for interactive systems provide a means of effectively translating abstract designs and usability principles into an executable form. These tools provide different levels of services for the programmer. Windowing systems are a central environment for both the programmer and user of an interactive system, allowing a single workstation to support separate user-system threads of action simultaneously. Interaction toolkit abstract away from the physical separation of input and output devices, allowing the programmer to describe behaviors of objects at a level similar to how the user perceives them. User interface management systems are the final level of programming support tools, allowing the designer and programmer to control the relationship between the presentation objects of a toolkit with their functional semantics in the actual application.

8.2 ELEMENTS OF WINDOWING SYSTEMS

A windowing system is its ability to provide programmer independence from the specifics of the hardware devices. A typical workstation will involve some visual display screen, a keyboard and some pointing device, such as a mouse. Any variety of these hardware devices can be used in any interactive system and they are all different in terms of the data they communicate and the commands that are used to instruct them.

A given windowing system will have a fixed generic language for the abstract terminal which is called its imaging model. The imaging models are sufficient to describe very arbitrary images. For efficiency reasons, specific primitives are used to handle text images, either as specific pixel images or as more generic font definitions.

Examples of imaging models 

Pixels The display screen is represented as a series of columns and rows of points – or pixels – which can be explicitly turned on or off, or given a color. This is a common imaging model for personal computers and is also used by the X windowing system.

Graphical kernel system (GKS) 
An international standard which models the screen as a collection of connected segments, each of which is a macro of elementary graphics commands.

Programmer’s hierarchical interface to graphics (PHIGS) 
Another international standard, based on GKS but with an extension to model the screen as editable segments.

PostScript
A programming language developed by Adobe Corporation which models the screen as a collection of paths which serve as infinitely thin boundaries or stencils which can be filled in with various colors or textured patterns and images.

8.2.1 ARCHITECTURE OF WINDOWING SYSTEMS

Bass and Coutaz [29] identify three possible architectures for the software to implement the roles of a windowing system. 

A classic example of a window system based on the client–server architecture is the industry-standard X Window System (Release 11), developed at the Massachusetts Institute of Technology (MIT) in the mid-1980s. Figure 8.3 shows the software architecture of X. X (or X11), as we mentioned earlier, is based on a pixel-based imaging model and assumes that there is some pointing mechanism available. What distinguishes X from other window systems, and the reason it has been adopted as a standard, is that X is based on a network protocol which clearly defines the server–client communication. The X Protocol can be implemented on different computers and operating systems, making X more device independent. 

The X server performs the following tasks:

* allows (or denies) access to the display from multiple client applications;
* interprets requests from clients to perform screen operations or provide other information;
* demultiplexes the stream of physical input events from the user and passes them to the appropriate     client;
* minimizes the traffic along the network by relieving the clients from having to keep track of certain    display information, like fonts, in complex data structures that the clients can access by ID numbers.

 Evaluation

1. It is the core support for separate and simultaneous user-system activity.

(a). windowing systems                                                 b. programming tools

c. programming applications                                            d. interaction toolkit

2. It has levels of services for programmers.

a. windowing systems                                                      (b). programming tools

c. programming applications                                             d. interaction toolkit

3. It brings programming closer to level of user perception

a. windowing systems                                                      b. programming tools

c. programming applications                                           (d) . interaction toolkit

4. It controls relationship between presentation and functionality.

a. windowing systems                                                      b. programming tools

(c). user interface management system                      d. interaction toolkit

5. Which of the following is NOT part of the layers of development tools?

a. windowing systems                                                      b. interaction toolkits

c. user interface management systems                          (d.). system model

6. It is about programming the abstract terminal device drivers

image models for output and (partially) input.

a. device update                                                              b. system update

(c). device independence                                              d. software quality

7. It is achieving simultaneity of user tasks.

a. communication point                                                    b. file back up

c. file sharing                                                                   (d). resource sharing

8. Which of the following is NOT part of the possible software architecture.

a. each application manages all processes

b. management role within kernel of operating system

c. management role as separate application

(d). each devices are connected to a network

9. It has pixel imaging model with some pointing mechanism.

a. Pixel Software architecture                                         b. System architecture

c. Mac architecture                                                         (d). X Windows architecture

10. It affects the interfaces especially modal dialogue box and non-modal dialogue box.

a. system file                                                                  (b). system style

c. program information                                                    d. file category

11. It can be an input, output and intrinsically linked.

(a). interaction object                                                   b. linked object

 c. attached object                                                          d .embedded objects

12. It is a type of AWT (abstract windowing toolkit) .

(a). Java toolkit                                                             b. Web toolkit

 c. Electrical Toolkit                                                        d. Mechanical Toolkit

13. This toolkit built on top of AWT with higher level features.

a. run toolkit                                                                  (b). swing toolkit

c. error toolkit                                                                 d. function toolkit

14. Which of the following is NOT part of the concern of User Interface Management Systems (UIMS)?

a. conceptual architecture                                             (b). manual techniques

c. implementation techniques                                         d. support infrastructure

15. It is an example of a UI development environment

 a. web sitemaps                                                             b. C programming language

(c). Visual Basic                                                            d. COBOL (Common Business-
                                                                                            Oriented Language

16. It has separation between application semantics and presentation.

 a. UIMS model algorithms                                             b. UIMS system design

(c). UIMS conceptual architecture                              d. UIMS interface

17. Which of the following is an example of lexica under Seeheim model?

a. dialogue control                                                         (b). presentation

c. functionality                                                                 d. dependence

18. Which of the following is an example of syntactic under Seeheim model?

(a). dialogue control                                                     b. Presentation

c. Functionality                                                               d. Dependence

19. Which of the following is an example of semantic under Seeheim model?

a. Dialogue control                                                         b. Presentation

(c). Functionality                                                          d. Dependence

20. It arose out of implementation experience but principal contribution is conceptual.

a. Arch model                                                                 b. Waterfall model

(c). Seeheim model                                                      d. Slinky model

21. It draws components on screen and set actions with scripts or links to program.

a. graphical identification                                                b. graphical user

c. graphical interaction                                                  (d). graphical specification

22. 

Which of the following is NOT a technique for a dialogue controller?

a. menu networks                                                          b. grammar notations

c. declarative language                                                (d). manual errors

23. It manages hierarchy and multiple views.

(a). PAC model                                                             b. Seeheim model

c. MVC model                                                                d. Slinky model

24. It is largely a pipeline model with graphics interface.

a.  PAC model                                                               b. Seeheim model
(c). MVC model                                                            d. Slinky model

25. It has more layers and distinguishes lexical/physical like a ‘slinky’ spring different layers may be thicker (more important) in different systems.

a. PAC model                                                                  b. Seeheim model

c. MVC model                                                                (d). Slinky model

26. 

It is a kind of feedback like a movement of mouse.

(a). lexical                                                                       b. syntactic

c. Semantic                                                                      d. logical

27. It is a kind of feedback like a menu highlights.

a. Lexical                                                                        (b). syntactic

c. Semantic                                                                     d. logical

28. It is a kind of feedback like a sum of numbers changes.

 a. Lexical                                                                         b. syntactic

(c). semantic                                                                   d. logical

29. It has independent of application semantics or presentation.

 a. internal control                                                            b. presentation control

(c). external control                                                       d. input control

30. It has read-evaluation loop for a system software.

(a). internal control                                                        b. presentation control

 c. external control                                                           d. input control