Scott Weinstein

PROVIDING A UNIFIED ACCOUNT OF DEFINITE NOUN PHRASES IN DISCOURSE

Citation Grosz, Barbara J., Aravind K. Joshi, and Scott Weinstein. 1983. Providing a unified account of definite noun phrases in discourse. In 21st Annual Meeting of the Association for Computational Linguistics: proceedings of the conference : 15-17 June 1983, Massachusetts Institute of Technology, Cambridge, Massachusetts, ed. Association for Computational Linguistics, 44-50. Morristown, N.J.: Association for Computational Linguistics.

Constraints for semistructured data and XML

Integrity constraints play a fundamental role in database design. We review initial work on the expression of integrity constraints for semistructured data and XML.

Path constraints on semistructured and structured data

We present a class of path constraints of interest in connection with both structured and semistructured databases, and investigate their associated implication problems. These path constraints are capable of expressing natural integrity constraints that are not only a fundamental part of the semantics of the data, but are also important in query optimization. We show that in semistructured databases, despite the simple syntax of the constraints, their associated implication problem is r.e. complete and nite implication problem is co-r.e. complete. However, we establish the decidability of the implication problems for several fragments of the path constraint language, and demonstrate that these fragments su ce to express important semantic information such as inverse relationships and local database constraints commonly found in object-oriented databases. We also show that in the presence of types, the analysis of path constraint implication becomes more delicate. We demonstrate some simple decidability results for two practical object-oriented data models.

Formal Learning Theory

Disputes about human nature inevitably evolve into disputes about the acquisition of knowledge, since the core issue in each controversy is the interaction of environment and human genetic endowment. Over the past two decades, a novel approach to this interaction has been developed by automata theorists and mathematicians. Within this approach, the impact of experience on the emerging competence of an organism is construed as a species of functional dependency. Using methods proper to the theory of computation, this construal has yielded mathematical insights that occasionally permit speculation about the acquisition of competence to be cast in sharper terms than heretofore. This cluster of related mathematical results has come to be known as (formal) learning theory. 1

Learning Theory and Natural Language

Abstract Formal Learning Theory may be conceived as a means of relating theories of comparative grammar to studies of linguistic development. After a brief review of relevant concepts, the present paper surveys formal results within Learning Theory that suggest correponding constraints on linguistic theory. Particular attention is devoted to the question: How many possible natural languages are there?

Path Constraints in Semistructured Databases

We investigate a class of path constraints that is of interest in connection with both semistructured and structured data. In standard database systems, constraints are typically expressed as part of the schema, but in semistructured data there is no explicit schema and path constraints provide a natural alternative. As with structured data, path constraints on semistructured data express integrity constraints associated with the semantics of data and are important in query optimization. We show that in semistructured databases, despite the simple syntax of the constraints, their associated implication problem is r.e. complete and finite implication problem is co-r.e. complete. However, we establish the decidability of the implication and finite implication problems for several fragments of the path constraint language and demonstrate that these fragments suffice to express important semantic information such as extent constraints, inverse relationships, and local database constraints commonly found in object-oriented databases.

A note on formal learning theory

A defining feature of natural language is that precisely the natural languages can be learned by normal human infants in the ordinary way.’ Consequently, one sondition on a theory of natural language is that it specify a class of languages that are learnable in this sense. Call this the Zearnabiiity condition. In a seminal paper, Gold (1967) offered a precise formulation of the leamability condition, a formulation that has already played a useful role in evaluating contemporary theories of natural language (see Pinker, 1979; Wexler and Culicover, 1980). Central to Gold’s treatment is the definition of ‘language identification in the limit’.” The purpose of the present note IS to expose a limitation in that definition, and thus to raise doubts about the a,)propriateness of the learnability condition that is based upon it, We proceed as follows. After some formal preliminaries (Section l), the Gold definition of language identification is presented, along with the leamability condition based upon it (Section 2). In Section -3, we criticize the Gold definition and its associated learnability cond.ition; ;i new definition of language identification is offered, and its consequences are discussed. Concluding remarks occupy Section 4.

Interaction between path and type constraints

XML [7], which is emerging as an important standard for data exchange on the World Wide Web, highlights the importance of the semistructured data. Although the XML standard itself does not require any schema or type system, a number of proposals [6, 15, 18] have been developed that roughly correspond to data definition languages. These allow one to constrain the structure of XML data by imposing a schema on it. These and other proposals also advocate the need for integrity constraints, another form of constraints that should, for example, be capable of expressing inclusion constraints and inverse relationships. The latter have recently been studied as path constraints in the context of semistructured data [4, 11]. It is likely that future XML proposals will involve both forms of constraint, and it is therefore appropriate to understand the interaction between them. This paper investigates that interaction. In particular it studies constraint implication problems, which are important both in understanding the semantics of type/constraint systems and in query optimization. A number of results on path constraint implication are established in the presences and absences of type systems. These results demonstrate that adding a type systems may in some cases simplify reasoning about path constraints and in other cases make it harder. For example, it is shown that there is a path constraint implication problem that is decidable in PTIME in the untyped context, but that becomes undecidable when a type system is added. On the other hand, there is an implication problem that is undecidable in the untyped context, but becomes not only decidable in cubic time but also finitely axiomatizable when a type system is imposed. Comments University of Pennsylvania Department of Computer and Information Science Technical Report No. MSCIS-98-16. This technical report is available at ScholarlyCommons: http://repository.upenn.edu/cis_reports/106

Aggregating inductive expertise

The aggregation problem is to design an inferential agent that makes intelligent use of the theories offered by a team of inductive inference machines working in a common environment. The present paper formulates several versions of the aggregation problem and investigates them from a recursion theoretic point of view.

Query Optimization for Semistructured Data Using Path Constraints in a Deterministic Data Model

Path constraints have been studied for semistructured data modeled as a rooted edge-labeled directed graph [4, 11-13]. In this model, the implication problems associated with many natural path constraints are undecidable [11, 13]. A variant of the graph model, called the deterministic data model, was recently proposed in [10]. In this model, data is represented as a graph with deterministic edge relations, i.e., the edges emanating from any node in the graph have distinct labels. This model is more appropriate for representing, e.g., ACeDB [27] databases and Web sites. This paper investigates path constraints for the deterministic data model. It demonstrates the application of path constraints to, among others, query optimization. Three classes of path constraints are considered: the language Pc introduced in [11], an extension of Pc, denoted by Pcw, by including wildcards in path expressions, and a generalization of Pcw, denoted by P*c, by representing paths as regular expressions. The implication problems for these constraint languages are studied in the context of the deterministic data model. It is shown that in contrast to the undecidability result of [11], the implication and finite implication problems for Pc are decidable in cubic-time and are finitely axiomatizable. Moreover, the implication problems are decidable for Pcw. However, the implication problems for P*c are undecidable.