We propose a novel formalism, called Frame Logic (abbr., F-logic), that accounts in a clean and declarative fashion for most of the structural aspects of object-oriented and frame-based languages. These features include object identity, complex objects, inheritance, polymorphic types, query methods, encapsulation, and others. In a sense, F-logic stands in the same relationship to the objectoriented paradigm as classical predicate calculus stands to relational programming. F-logic has a model-theoretic semantics and a sound and complete resolution-based proof theory. A small number of fundamental concepts that come from object-oriented programming have direct representation in F-logic; other, secondary aspects of this paradigm are easily modeled as well. The paper also discusses semantic issues pertaining to programming with a deductive object-oriented language based on a subset of F-logic.

This paper proposes a new logic programming language called GOLOG whose interpreter automatically maintains an explicit representation of the dynamic world being modeled, on the basis of user supplied axioms about the preconditions and effects of actions and the initial state of the world. This allows programs to reason about the state of the world and consider the effects of various possible courses of action before committing to a particular behavior. The net effect is that programs may be written at a much higher level of abstraction than is usually possible. The language appears well suited for applications in high level control of robots and industrial processes, intelligent software agents, discrete event simulation, etc. It is based on a formal theory of action specified in an extended version of the situation calculus. A prototype implementation in Prolog has been developed.

We propose Concurrent Transaction Logic (CT R) as the language for specifying, analyzing, and scheduling of workflows. We show that both local and global properties of workflows can be naturally represented as CT R formulas and reasoning can be done with the use of the proof theory and the semantics of this logic. We describe a transformation that leads to an efficient algorithm for scheduling workflows in the presence of global temporal constraints, which leads to decision procedures for dealing with several safety related properties such as whether every valid execution of the workflow satisfies a particular property or whether a workflow execution is consistent with some given global constraints on the ordering of events in a workflow. We also...

In previous work, we developed Transaction Logic (or T R), which deals with state changes in deductive databases. T R provides a logical framework in which elementary database updates and queries can be combined into complex database transactions. T R accounts not only for the updates themselves, but also for important related problems, such as the order of update operations, non-determinism, and transaction failure and rollback. In the present paper, we propose Concurrent Transaction Logic (or CT R), which extends Transaction Logic with connectives for modeling the concurrent execution of complex processes. Concurrent processes in CT R execute in an interleaved fashion and can communicate and synchronize themselves. Like classical logic, CT R has a "Horn" fragment that has both a procedural and a declarative semantics, in which users can program and execute database transactions. CT R is thus a deductive database language that integrates concurrency, communication, and updates. All th...

In this paper, we show that there is a simple connection between logic programming and planning. The main result of this paper is the following: given any planning domain consisting of an initial state, and a set of operation definitions, this domain can be translated, in linear-time, to a logic program such that a given goal G is achievable in the planning domain iff a related goal G ? is true in some stable model of the logic program obtained by the translation. We show that this translation yields at least two interesting consequences: (1) methods to update databases can be used to handle surprises when executing plans (i.e. a surprise occurs when an initial plan is partly executed, but one of the resulting intermediate states differs, perhaps due to external reasons, from what is predicted). (2) rigid actions, which are actions that must be executed when their pre-conditions are true, can be easily accommodated within our framework as well. 1 Introduction One of the fundamental ...

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

: We propose an extension of classical predicate calculus, called Transaction Logic, which provides a logical foundation for the phenomenon of state changes in logic programs and databases. Transaction Logic comes with a natural model theory and a sound and complete proof theory. The proof theory not only verifies programs, but also executes them, which makes this logic an ideal tool for declarative programming of database transactions and state-modifying logic programs. The semantics of Transaction Logic leads naturally to features whose amalgamation in a single logic has proved elusive in the past. These features include hypothetical and committed updates, dynamic constraints on transaction execution, non-determinism, and bulk updates. Finally, Transaction Logic holds promise as a logical model of hitherto non-logical phenomena, including so-called procedural knowledge in AI, and the behavior of object-oriented databases, especially methods with side effects. This paper presents the...

We study data-driven Web services provided by Web sites interacting with users or applications. The Web site can access an underlying database, as well as state information updated as the interaction progresses, and receives user input. The structure and contents of Web pages, as well as the actions to be taken, are determined dynamically by querying the underlying database as well as the state and inputs. The properties to be verified concern the sequences of events (inputs, states, and actions) resulting from the interaction, and are expressed in linear or branchingtime temporal logics. The results establish under what conditions automatic verification of such properties is possible and provide the complexity of verification. This brings into play a mix of techniques from logic and automatic verification.

The design of webbases, database systems for supporting Webbased applications, is currently an active area of research. In this paper, we propose a 3-layer architecture for designing and implementing webbases for querying dynamic Web content (i.e., data that can only be extracted by filling out multiple forms). The lowest layer, virtual physical layer, provides navigation independence by shielding the user from the complexities associated with retrieving data from raw Web sources. Next, the traditional logical layer supports site independence. The top layer is analogous to the external schema layer in traditional databases. Within this architectural framework we address two problems unique to webbases — retrieving dynamic Web content in the virtual physical layer and querying of the external schema by the end user. The layered architecture makes it possible to automate data extraction to a much greater degree than in existing proposals. Wrappers for the virtual physical schema can be created semiautomatically, by asking the webbase designer to navigate through the sites of interest — we call this approach mapping by example. Thus, the webbase designer need not have expertise in the language that maps the physical schema to the raw Web (this should be contrasted to other approaches, which require expertise in various Web-enabled flavors of SQL). For the external schema layer, we propose a semantic extension of the universal relation interface. This interface provides powerful, yet reasonably simple, ad hoc querying capabilities for the end user compared to the currently prevailing “canned” form-based interfaces on the one hand or complex Web-enabling extensions of SQL on the other. Finally, we discuss the implementation of the proposed architecture.

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