Yuri Leontiev

Temporal granularity for unanchored temporal data

Granularity is an integral feature of bothanchored(e.g., 25 October 1995 , July 1996) andunanchored(e.g.,3 minutes, 6 hours 20 minutes , 5 days, 1 week) temporal data. In supporting temporal data that is specified in different gran ularities, numerous approaches have been proposed to deal with the issues of converting temporal data from one granularity to another. The emphasis, however, has only been on granularity conversions with respect to anchored temporal data. This is because a granularity in these approaches i s modeled as an anchoredpartitioning of the time axis, thereby making it difficult to deal with granularity conversions in u anchored temporal data. In this paper we provide a novel approach to the treatment of granularity in temporal data. A granularity is modeled as a special kind of unanchored temporal primitive that can be used as a unit of time. That is, a granularity is modeled as a unit unanchored temporal primitive. Granularities are accommodated within the context of calendarsand granularity conversions are presented and discussed in terms of unanchored durations of time. This allows us to consistently model and operate on unanchored temporal data that is comprised of different and mixed granularities. Specifically, we show how unanchored temporal data is represented, give procedures for converting the data to a given granularity, provide canonical forms for the data, an d describe how operations between the data are performed.

Multi-method Dispatch Using Multiple Row Displacement

Multiple Row Displacement (MRD) is a new dispatch technique for multi-method languages. It is based on compressing an n-dimensional table using an extension of the single-receiver row displacement mechanism. This paper presents the new algorithm and provides experimental results that compare it with implementations of existing techniques: compressed n-dimensional tables, look-up automata and single-receiver projection. MRD uses comparable space to the other techniques, but has faster dispatch performance.

Modeling temporal primitives: back to basics

The fundamental question about a temporal model is “what is its underlying temporal structure?” More specifically, what are the temporal primitives supported in the model, what temporal domains are available over these primitives, and whether the primitives are determinate or indeterminate? In this paper a simple, general framework for supporting temporal primitives (instants, intervals, sets of intervals) is presented. The framework allows seamless integration of dense and discrete temporal domains of time over a linearly ordered, unbounded point structure. The framework also provides a set-theoretic basis that allows uniform treatment of determinate and indeterminate temporal primitives.

Modeling Time: Back to Basics

Most of the work in modeling time in information systems has concentrated on issues such as support for historical information and providing query facilities to manipulate such information. In doing so, some simplistic view of the underling nature of time has been assumed. However, the domain of time is far from being simplistic. In this paper, we outline the various issues which arise in modeling basic temporal entities and propose solutions to these issues. More speci cally, we note that the nature of temporal information can either be anchored (e.g., October 25; 1995) or unanchored (e.g., 1 week), and is usually available in multiple granularities (e.g., the airline ight departure and arrival times are usually given in minutes, while the history of the salary of an employee is usually recorded in days). Physical temporal information also needs to be represented in a manner so as to be human readable. This is achieved using calendars. In this work, we show how both anchored and unanchored temporal entities are represented within the context of calendars. We discuss how calendars provide relationships between multiple granularities and facilitate the conversion of anchored and unanchored times from one granularity to another. We also give the semantics of various operations on anchored and unanchored times.

A Uniform Behavioral Temporal Object Model

In this work we present a uniform behavioral temporal object model which includes a rich and extensible set of types and behaviors to support various notions of time. Our temporal model supports the continuous and discrete domains of time. It also supports various speci cations of time namely, time instants, time intervals, and time spans. Two issues which deal with temporal information that frequently arise in real-world applications are the need to consistently store and operate on temporal information that is comprised of di erent granularities, and the ability to represent indeterminate temporal information. Temporal indeterminacy arises when we know for certain that an event did occur, but exactly when it occured is unknown. Our model provides a uniform framework that supports di erent granularities of time and temporal indeterminacy. We show how di erent granularities can be converted to each other, and how this leads to temporal indeterminacy. We further show how continuous and discrete indeterminate time intervals, spans, and instants are consistently modeled in our framework.

Type system for an object-oriented database programming language

The concept of an object-oriented database programming language (OODBPL) is appealing because it has the potential of combining the advantages of object orientation and database programming to yield a powerful and universal programming language design. A uniform and consistent combination of object orientation and database programming, however, is not straightforward. Since one of the main components of an object-oriented programming language is its type system, one of the first problems that arise during an OODBPL design is related to the development of a uniform, consistent, and theoretically sound type system that is sufficiently expressive to satisfy the combined needs of object orientation and database programming. This dissertation presents the design of a type system suitable for object-oriented database programming. The type system has a unique combination of uniformity, expressibility, verifiability, and theoretically proven soundness. It also possesses features that make it suitable for database programming, such as seamless integration of imperative types and features, precise query typing via union and intersection types, separation among three abstraction layers providing a high degree of code reuse, parametric polymorphism, extensibility, and dynamic type analysis capabilities. In the process of type system development, a theoretical framework for dealing with type systems that combine parametric and inclusion polymorphism is established. Due to its modular construction, this framework can be easily extended and used beyond the scope of this dissertation. Another contribution of this work is an extensive analysis of existing and proposed type systems from the point of view of the set of requirements related to object orientation and database programming. This research leads to the development of a uniform and theoretically sound OODBPL that can successfully utilize the power inherent in both object orientation and database programming paradigms. This will eventually lead to the development and implementation of a uniform object-oriented database system that will use the OODBPL as its main programming and query engine.