propositions that do not need an action to support them will wind up taking the null value by default. There are two types of constraints—the mutex constraints which say that certain proposition action combinations are infeasible, and activation constraints which state that when a proposition p takes an action a as its value, the propositions corresponding to the preconditions of a cannot then take null (“⊥”) values.
5.2. Communicating failure to the planner
If the resource allocation fails, the reason for the failure has to be extracted and communicated to the planner. The three steps are detailed next.
Explanation generation
Generating failure explanation for the scheduler can be done in a straightforward fashion by using the explanation-based backtracking techniques [18,19]. Specifically, if we employ a conflict-directed backjumping strategy [19,43] to guide the solution of the scheduling CSP, in the event the CSP cannot be solved, the conflict set at the root of the search tree shows the subset of variables of the scheduling CSP that are causing the failure.
Explanation translation
After we get the failure explanations from the scheduler in the form of nogoods, NG = (X 1 ,X 2 ,...,X n ), we have to transform them into the form that the planner can understand. On the face of it, this problem seems trivial—after all, as shown in Fig. 10, the variables of the scheduler should correspond to actions in the planner, and thus they should make sense to the planner directly. There are, however, two complicating factors:
• Contrary to the simplified view illustrated in Fig.10,the variables of the CSP problem, as set up in Section 4.1, do not have a one-to-one correspondence with the actions in the causal plan (see Fig. 23). Instead, the relation is more indirect—in terms of resource spans, positions, etc., some of which don’t make direct sense to the planner. Specifically, each variable in the scheduler’s CSP, and consequently in any failure
propositions that do not need an action to support them will wind up taking the null value by default. There are two types of constraints—the mutex constraints which say that certain proposition action combinations are infeasible, and activation constraints which state that when a proposition p takes an action a as its value, the propositions corresponding to the preconditions of a cannot then take null (“⊥”) values.5.2. Communicating failure to the plannerIf the resource allocation fails, the reason for the failure has to be extracted and communicated to the planner. The three steps are detailed next.Explanation generationGenerating failure explanation for the scheduler can be done in a straightforward fashion by using the explanation-based backtracking techniques [18,19]. Specifically, if we employ a conflict-directed backjumping strategy [19,43] to guide the solution of the scheduling CSP, in the event the CSP cannot be solved, the conflict set at the root of the search tree shows the subset of variables of the scheduling CSP that are causing the failure.Explanation translationAfter we get the failure explanations from the scheduler in the form of nogoods, NG = (X 1 ,X 2 ,...,X n ), we have to transform them into the form that the planner can understand. On the face of it, this problem seems trivial—after all, as shown in Fig. 10, the variables of the scheduler should correspond to actions in the planner, and thus they should make sense to the planner directly. There are, however, two complicating factors:•ขัดกับมุมมองแบบง่ายในตัวแปร Fig.10,the ของปัญหา CSP ภาพตามที่ตั้งค่าในส่วน 4.1 ไม่มีการติดต่อแบบหนึ่งต่อหนึ่งกับการดำเนินการในการเชิงสาเหตุวางแผน (ดูรูปที่ 23) แทน ความสัมพันธ์ที่เป็นทางอ้อมมากขึ้น — ในแง่ทรัพยากรครอบคลุม ตำแหน่ง ฯลฯ ซึ่งไม่ทำให้ความรู้สึกโดยตรงเพื่อ เฉพาะ แต่ละตัวแปรในตัวจัดกำหนดการ CSP และจากนั้นในความล้มเหลว
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