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.

We present a novel language for querying object-oriented databases. The language is built around the idea of extended path expressions that substantially generalize [ZAN83], and on an adaptation of the first-order formalization of object-oriented languages from [KW89, KLW90, KW92]. The language incorporates features not found in earlier proposals; it is easier to use and has greater expressive power. Some of the salient features of our language are: ffl Precise model-theoretic semantics. ffl A very expressive form of path expressions that not only can do joins, selections and unnesting, but can also be used to explore the database schema. ffl Views can be defined and manipulated in a much more uniform way than in other proposals. ffl Database schema can be explored in the very same language that is used to retrieve data. Unlike in relational languages, the user needs not know anything about the system tables that store schema information. ffl The notions of a type and type-correctness have precise meaning. It accommodates a wide variety of queries that might be deemed well- or ill-typed under different circumstances. In particular, we show that there is more than one way of settling the issue of type correctness. For expository purposes and due to space limitation, we chose to make a number of simplifying assumptions and left some features out. A more complete account can be found in [KSK92].

This paper describes a language that is intended to support software engineers in the development of information systems throughout the software lifecycle. This language is not a programming language. Following the example of a number of other software engineering projects, our work is based on the premise that information system development is knowledge-intensive and that the primary responsibility of any language intended to support this task is to be able to formally represent the relevant knowledge.

We describe a novel logic, called HiLog, and show that it provides a more suitable basis for logic programming than does traditional predicate logic. HiLog has a higher-order syntax and allows arbitrary terms to appear in places where predicates, functions and atomic formulas occur in predicate calculus. But its semantics is first-order and admits a sound and complete proof procedure. Applications of HiLog are discussed, including DCG grammars, higher-order and modular logic programming, and deductive databases.

Real-scale Semantic Web applications, such as Web Portals and E-Marketplaces, require the management of voluminous metadata repositories containing descriptive information (i.e., metadata) about the available Web resources and services. Better knowledge about the meaning, usage, accessibility or quality of these resources and services will considerably facilitate the automated processing of both Web content and services. In this context, the Resource Description Framework (RDF) enables the creation and exchange of metadata as any other Web data. Although large volumes of RDF descriptions are already appearing (e.g., as exported Portal catalogs or service descriptions), sufficiently expressive declarative languages for querying both RDF descriptions and schemas are still missing. In this paper, we propose RQL, a new RDF query language, relying on a formal graph model that permits the interpretation of superimposed resource descriptions. RQL is an OQL-inspired adaptation of XML query languages to the peculiarities of RDF but, foremost, is an extension of this functionality for uniformly querying both descriptions and schemas. We illustrate the syntax, semantics and core functionality of RQL bymeans of a set of benchmark queries and report on the performance of RSSDB, our persistent RDF Store, for storing and querying voluminous RDF descriptions.

One of the main tasks of mediators is to fuse information from heterogeneous information sources. This may involve, for example, removing redundancies, and resolving inconsistencies in favor of the most reliable source. The problem becomes harder when the sources are unstructured/semistructured and we do not have complete knowledge of their contents and structure. In this paper we show how many common fusion operations can be specified non-procedurally and succinctly. The key to our approach is to assign semantically meaningful object ids to objects as they are "imported " into the mediator.

Mediators are used for integration of heterogeneous information sources. We present a system for declaratively specifying mediators. It is targeted for integration of sources with unstructured or semi-structured data and/or sources with changing schemas. We illustrate the main features of the Mediator Specification Language (MSL), show how they facilitate integration, and describe the implementation of the system that interprets the MSL specifications.

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Information integration systems have to cope with the different and limited query interfaces of the underlying information sources. First, the integration systems need descriptions of the query capabilities of each source, i.e., the set of queries supported by each source. Second, the integration systems need algo-rithms for deciding how a query can be an-swered given the capabilities of the sources. Third, they need to translate a query into the format that the source understands. We present two languages suitable for descrip-tions of query capabilities of sources and com-pare their expressive power. We also de-scribe algorithms for deciding whether a query “matches ” the description and show their ap-plication to the problem of translating user queries into source-specific queries and com-mands. Finally, we propose new improved al-gorithms for the problem of answering queries using these descriptions. 1

Data integration often requires a clean abstraction of the different formats in which data are stored, and means for specifying the correspondences/relationships between data in different worlds and for translating data from one world to another. For that, we introduce in this paper a middleware data model that serves as a basis for the integration task, and a declarative rules language for specifying the integration. We show that using the language, correspondences between data elements can be computed in polynomial time in many cases, andmay require exponential time only when insensitivity to order or duplicates are considered. Furthermore, we show that in most practical cases the correspondence rules can be automatically turnedinto translation rules to map data from one representation to another. Thus, a complete integration task (derivation of correspondences, transformation of data from one world to the other, incremental integration of a new bulk of data, etc.) can be specified using a single set of declarative rules.