676 DESIGN CASE STUDY:MULTI-PANEL INTERACTIVE SYSTEMS $20.1 A typical panel,for the Enquiry on Flights state,might look like the following (only intended,however,to illustrate the ideas,and making no claim of realism or good ergonomic design).The screen is shown towards the end of a step;items in color italics are the user's answers,and items in bold color show an answer displayed by the system. -Enquiry on Flights- A panel Flight sought from: Santa Barbara To: Paris Departure on or after: 21Nov On or before: 22 Nov Preferred airline(s): Special requirements: AVAILABLE FLIGHTS:1 FIt#AA 42 Dep 8:25 Arr 7:45 Thru:Chicago Choose next action: 0一Exit 1-Help 2-Further enquiry 3-Reserve a seat The session begins in an initial state,and ends whenever it reaches a final state.We The figure also can represent the overall structure by a transition graph showing the possible states and include state num- the transitions between them.The edges of the graph are labeled by integers bers,for use later in the discussion. corresponding to the possible user choices for the next step at the end of a state.At the top of the facing page is a graph for a simple airline reservation system. The problem is to come up with a design and implementation for such applications, achieving as much generality and flexibility as possible.In particular: GI.The graph may be large.It is not uncommon to see applications with several hundred states and correspondingly many transitions. G2.The structure is subject to change.The designers are unlikely to foresee all the possible states and transitions.As users start exercising the system,they will come up with requests for changes and additions. G3.Nothing in the given scheme is specific to the choice of application:the airline reservation mini-system is just a working example.If your company needs a number of such systems,either for its own purposes or (in a software house)for various customers,it will be a big benefit to define a general design or,better yet, a set of modules that you can reuse from application to application.676 DESIGN CASE STUDY: MULTI-PANEL INTERACTIVE SYSTEMS §20.1 A typical panel, for the Enquiry on Flights state, might look like the following (only intended, however, to illustrate the ideas, and making no claim of realism or good ergonomic design). The screen is shown towards the end of a step; items in color italics are the user’s answers, and items in bold color show an answer displayed by the system. The session begins in an initial state, and ends whenever it reaches a final state. We can represent the overall structure by a transition graph showing the possible states and the transitions between them. The edges of the graph are labeled by integers corresponding to the possible user choices for the next step at the end of a state. At the top of the facing page is a graph for a simple airline reservation system. The problem is to come up with a design and implementation for such applications, achieving as much generality and flexibility as possible. In particular: G1 • The graph may be large. It is not uncommon to see applications with several hundred states and correspondingly many transitions. G2 • The structure is subject to change. The designers are unlikely to foresee all the possible states and transitions. As users start exercising the system, they will come up with requests for changes and additions. G3 • Nothing in the given scheme is specific to the choice of application: the airline reservation mini-system is just a working example. If your company needs a number of such systems, either for its own purposes or (in a software house) for various customers, it will be a big benefit to define a general design or, better yet, a set of modules that you can reuse from application to application. A panel – Enquiry on Flights – Flight sought from: Departure on or after: To: On or before: Preferred airline (s): Special requirements: AVAILABLE FLIGHTS: 1 Flt# AA 42 Dep 8:25 Arr 7:45 Thru: Chicago Choose next action: 0 — Exit 1 — Help 2 — Further enquiry 3 — Reserve a seat Santa Barbara 21 Nov Paris 22 Nov The figure also include state num￾bers, for use later in the discussion