tailieunhanh - Software Engineering A PRACTITIONER’S APPROACH phần 8

một quá trình thiết kế tổ chức phải được tiến hành. Thiết kế giao diện người dùng bắt đầu với việc xác định người sử dụng, nhiệm vụ, và các yêu cầu môi trường. Nhiệm vụ phân tích là một hoạt động thiết kế xác định nhiệm vụ của người sử dụng và hành động bằng cách sử dụng một cách tiếp cận elaborative hoặc hướng đối tượng. | 596 PART FOUR OBJECT-ORIENTED SOFTWARE ENGINEERING FIGURE A representation of active state transitions an object-behavior model is a simple representation of the active states for each object and the events triggers that cause changes between these active states. Figure illustrates a simple representation of active states for the control panel object in the SafeHome system. Each arrow shown in Figure represents a transition from one active state of an object to another. The labels shown for each arrow represent the event that triggers the transition. Although the active state model provides useful insight into the life history of an object it is possible to specify additional information to provide more depth in understanding the behavior of an object. In addition to specifying the event that causes the transition to occur the analyst can specify a guard and an action CHA93 . A guard is a Boolean condition that must be satisfied in order for the transition to occur. For example the guard for the transition from the at rest state to the comparing state in Figure can be determined by examining the use-case if password input 4 digits then make transition to comparing state In general the guard for a transition usually depends upon the value of one or more attributes of an object. In other words the guard depends on the passive state of the object. An action occurs concurrently with the state transition or as a consequence of it and generally involves one or more operations responsibilities of the object. For example the action connected to the password entered event Figure is an operation that accesses a password object and performs a digit-by-digit comparison to validate the entered password. CHAPTER 21 OBJECT-ORIENTED ANALYSIS 597 FIGURE A partial event trace for SafeHome Homeowner Control panel System System ready Enters password Initiates beep Beep sounded Ready for activation deactivation Selects stay away Activate deactivate .