Weak ontic necessity is the ontic necessity expressed by ``should'' or
``ought to'' in English. An example of it is ``I should be dead by now''. A
feature of this necessity is whether it holds does not have anything to do with
whether its prejacent holds. In this paper, we present a logical theory for
conditional weak ontic necessity based on context update. A context is a set of
ordered defaults, determining expected possible states of the present world.
Sentences are evaluated with respect to contexts. When evaluating the
conditional weak ontic necessity with respect to a context, we first update the
context with the antecedent, then check whether the consequent holds with
respect to the updated context. The logic is complete. Our theory combines
premise semantics and update semantics for conditionals.

本文提出了一种基于上下文更新的条件性弱本体必要性的逻辑理论，将前提语义和更新语义相结合。

基于环境更新的条件弱实在必要性逻辑理论

A logical theory for conditional weak ontic necessity based on context update

Logic programs under the stable model semantics, or answer-set programs,
provide an expressive rule-based knowledge representation framework, featuring
a formal, declarative and well-understood semantics. However, handling the
evolution of rule bases is still a largely open problem. The AGM framework for
belief change was shown to give inappropriate results when directly applied to
logic programs under a non-monotonic semantics such as the stable models. The
approaches to address this issue, developed so far, proposed update semantics
based on manipulating the syntactic structure of programs and rules.
More recently, AGM revision has been successfully applied to a significantly
more expressive semantic characterisation of logic programs based on SE-models.
This is an important step, as it changes the focus from the evolution of a
syntactic representation of a rule base to the evolution of its semantic
content.
In this paper, we borrow results from the area of belief update to tackle the
problem of updating (instead of revising) answer-set programs. We prove a
representation theorem which makes it possible to constructively define any
operator satisfying a set of postulates derived from Katsuno and Mendelzon's
postulates for belief update. We define a specific operator based on this
theorem, examine its computational complexity and compare the behaviour of this
operator with syntactic rule update semantics from the literature. Perhaps
surprisingly, we uncover a serious drawback of all rule update operators based
on Katsuno and Mendelzon's approach to update and on SE-models.

本文探讨了一种通过借鉴信仰更新领域的成果来解决更新 Logic 程序的问题的方法，证明了一种表示定理并定义了一种特定操作，从而更好地管理 Logic 程序的演变。