Abstract. Flora-2 is a rule-based object-oriented knowledge base system designed for a variety of automated tasks on the Semantic Web, ranging from meta-data management to information integration to intelligent agents. The Flora-2 system integrates F-logic, HiLog, and Transaction Logic into a coherent knowledge representation and inference language. The result is a flexible and natural framework that combines rule-based and object-oriented paradigms. This paper discusses the principles underlying the design of the Flora-2 system and describes its salient features, including meta-programming, reification, logical database updates, encapsulation, and support for dynamic modules. 1

Abstract. Current technologies for Web Services are based on syntactical descriptions and, therefore, lend themselves to only limited amount of automation. Research efforts in Semantic Web Services, such as WSMO, try to overcome this major deficiency by providing a complete semantic description for Web Services and their related aspects. In this paper we present a logical framework which exploits such formal descriptions in order to dynamically discover Web Services that match requester goals. We consider two kinds of user goals: discovery and contracting. Based on the WSMO conceptual model, we define proof obligations that formalize the concepts of a match in these two cases. We also describe a concrete realization of this framework in the F-Logic reasoning engine F LORA-2. Such a realization requires an extension of F-Logic in order to support rule reification. With this extension, F-logic becomes a suitable framework for describing and reasoning about Semantic Web Services and their capabilities. 1

Abstract. Anonymous resources and meta statements are two of the more interesting features of RDF — an emerging standard for representing semantic information on the Web. Ironically, when RDF was standardized by W3C over three years ago [24], it came without a semantics. There is now growing understanding that a Semantic Web language without a semantics is an oxymoron, and a number of efforts are directed towards giving RDF a precise semantics [17,15,11]. In this paper we propose a simple semantics for anonymous resources and meta statements in F-logic [23] — a frame-based logic language, which is a popular formalism for representing and reasoning about semantic information on the Web [29,14,16,13,12]. The choice of F-logic (over RDF) as a basis for our semantics is motivated by the fact that F-logic provides a comprehensive solution for the problem of integrating frames, rules, inheritance, and deduction, and it has been shown to provide an effective inference service for RDF [13,28]. 1

A requirements analysis in the emerging field of Semantic Web Services (SWS) (see

. Transaction Logic was designed as a general logic of state change for deductive databases and logic programs. It has a model theory, a proof theory, and its Horn subset can be given a procedural interpretation. Previous work has demonstrated that the combination of declarative semantics and procedural interpretation turns the Horn subset of Transaction Logic into a powerful language for logic programming with updates [BK98,BK94,BK93,BK95]. In this paper, we focus not on the Horn subset, but on the full logic, and we explore its potential as a formalism for reasoning about logic programs with updates. We first develop a methodology for specifying properties of such programs, and then provide a sound inference system for reasoning about them, and conjecture a completeness result. Finally, we illustrate the power of the inference system through a series of examples of increasing difficulty. 1 Introduction Updates are a crucial component of any database programming language. Even the si...

. Updates are a crucial component of any database programming language. Even the simplest database transactions, such as withdrawal from a bank account, require updates. Unfortunately, updates are not accounted for by the classical Horn semantics of logic programs and deductive databases, which limits their usefulness in real-world applications. As a short-term practical solution, logic programming languages have resorted to handling updates using ad hoc operators without a logical semantics. A great many works have been dedicated to developing logical theories in which the state of the underlying database can evolve with time. Many of these theories were developed with specific applications in mind, such as reasoning about actions, database transactions, program verification, etc. As a result, the different approaches have different strengths and weaknesses. In this survey, we review a number of these works, discuss their application domains, and highlight their strong and weak points...

1 Introduction RDF [18] was proposed as a standard for representing semantic information on the Web. Ironically, the specification of RDF did not formally define a semantics. Fortunately this peculiar situation is currently being rectified by a number of efforts [12, 10].

Abstract not found

, and I.V. Ramakrishnan 2 1

: Traditional logic-based specification approaches fix the structure and the dynamics of an object system at specification time. Information systems are applications with a very long life-time. Therefore, object and specification evolution is needed to react to changing requirements. Hence, this is a relevant aspect of describing information systems as object societies. We present a logical specification framework for evolving objects. Our framework is based on the concepts of object developed for the languages Troll and Gnome and the underlying temporal logic OSL. The syntactic notion of object descriptions is extended to explicitly manipulate temporal axioms during behaviour evolution. An extension of OSL called dyOSL establishes a logical framework where basic temporal formulae are evaluated by a second logical layer. dyOSL allows to explicitly manipulate state-dependent sets of temporal formulae to model evolution of object axioms. 199 200 LOGICS FOR DATABASES AND INF...