Agent Theories, Architectures, and Languages: A Survey <s> Levesque -belief and awareness <s> As part of an on-going project to understand the foundations of Knowledge Representation, we are attempting to characterize a kind of belief that forms a more appropriate basis for Knowledge Representation systems than that captured by the usual possible-world formalizations begun by Hintikka. In this paper, we point out deficiencies in current semantic treatments of knowledge and belief (including recent syntactic approaches) and suggest a new analysis in the form of a logic that avoids these shortcomings and is also more viable computationally. <s> BIB001 </s> Agent Theories, Architectures, and Languages: A Survey <s> Levesque -belief and awareness <s> Several new logics for belief and knowledge are introduced and studied, all of which have the property that agents are not logically omniscient. In particular, in these logics, the set of beliefs of an agent does not necessarily contain all valid formulas. Thus, these logics are more suitable than traditional logics for modelling beliefs of humans (or machines) with limited reasoning capabilities. Our first logic is essentially an extension of Levesque's logic of implicit and explicit belief, where we extend to allow multiple agents and higher-level belief (i.e., beliefs about beliefs). Our second logic deals explicitly with "awareness," where, roughly speaking, it is necessary to be aware of a concept before one can have beliefs about it. Our third logic gives a model of "local reasoning," where an agent is viewed as a "society of minds," each with its own cluster of beliefs, which may contradict each other. <s> BIB002 </s> Agent Theories, Architectures, and Languages: A Survey <s> Levesque -belief and awareness <s> Logics of belief play an essential role in formal approaches to knowledge representation (KR). Such logics allow us to formalize the idea that a knowledge base (KB) represents an epistemic state, that is, a set of beliefs. In its simplest form, an epistemic state can be defined as the set of all beliefs that logically follow from believing the sentences that are explicitly stored in the KB. Reasoning can be understood as computing whether a belief follows logically from believing the sentences in the KB. Since the classical model of belief, possible-world semantics, renders reasoning undecidable, it is important to find weaker models with better computational properties. <s> BIB003 </s> Agent Theories, Architectures, and Languages: A Survey <s> Levesque -belief and awareness <s> 1. Logic 2. Information 3. Situation theory 4. Meaning and constraints 5. Some logical issues 6. Mental states 7. Perception and action 8. Situation semantics 9. Topics in situation semantics 10. Historical perspectives and future directions. <s> BIB004
In a 1984 paper, Levesque proposed a solution to the logical omniscience problem that involves making a distinction between explicit and implicit belief BIB001 . Crudely, the idea is that an agent has a relatively small set of explicit beliefs, and a very much larger (infinite) set of implicit beliefs, which include the logical consequences of the explicit beliefs. To formalise this idea, Levesque developed a logic with two operators; one each for implicit and explicit belief. The semantics of the explicit belief operator were given in terms of a weakened possible worlds semantics, by borrowing some ideas from situation semantics  BIB004 . The semantics of the implicit belief operator were given in terms of a standard possible worlds approach. A number of objections have been raised to Levesque's model [109, p135] : first, it does not allow quantification -this drawback has been rectified by Lakemeyer BIB003 ; second, it does not seem to allow for nested beliefs; third, the notion of a situation, which underlies Levesque's logic is, if anything, more mysterious than the notion of a world in possible worlds; and fourth, under certain circumstances, Levesque's proposal still makes unrealistic predictions about agent's reasoning capabilities. In an effort to recover from this last negative result, Fagin and Halpern have developed a 'logic of general awareness', based on a similar idea to Levesque's but with a very much simpler semantics BIB002 . However, this proposal has itself been criticised by some  .