Randal J. Peters

Tigukat: a uniform behavioral objectbase management system

We describe the TIGUKAT objectbase management system, which is under development at the Laboratory for Database Systems Research at the University of Alberta. TIGUKAT has a novel object model, whose identifying characteristics include a purely behavioral semantics and a uniform approach to objects. Everything in the system, including types, classes, collections, behaviors, and functions, as well as meta-information, is a first-class object with well-defined behavior. In this way, the model abstracts everything, including traditional structural notions such as instance variables, method implementation, and schema definition, into a uniform semantics of behaviors on objects. Our emphasis in this article is on the object model, its implementation, the persistence model, and the query language. We also (briefly) present other database management functions that are under development such as the query optimizer, the version control system, and the transaction manager.

Axiomatization of dynamic schema evolution in object bases

The schema of a system consists of the constructs that model its entities. Schema evolution is the timely change and management of the schema. Dynamic schema evolution is the management of schema changes while the system is in operation. We propose a sound and complete axiomatic model for dynamic schema evolution in object-base management systems (OBMSs) that support subtyping and property inheritance. The model is formal, which distinguishes it from the traditional approach of informally defining a number of invariants and rules to enforce them. By reducing systems to the axiomatic model, their functionality with respect to dynamic schema evolution can be compared within a common framework.<<ETX>>

Reflection in a Uniform Behavioral Object Model

We present the uniform meta-architecture of the TIGUKAT object model and show how it provides reflection in objectbase management systems. Reflection is the ability for a system to manage information about itself and to access (or reason about) this information through the regular access primitives of the model. The TIGUKAT object model is purely behavioral in nature, supports full encapsulation of objects, defines a clear separation between primitive components such as types, classes, collections, behaviors, functions, etc., and incorporates a uniform semantics over objects. The architecture of its meta-system is uniformly represented within itself, which gives a clean semantics for reflection.

Managing Schema Evolution Using a Temporal Object Model

The issues of schema evolution and temporal object models are generally considered to be orthogonal and are handled independently. This is unrealistic because to properly model applications that need incremental design and experimentation (such as CAD, software design process), the evolutionary histories of the schema objects should be traceable. In this paper we propose a method for managing schema changes by exploiting the functionality of a temporal object model. The result is a uniform treatment of schema evolution and temporal support for many object database management systems applications that require both.

An extensible query model and its languages for a uniform behavioral object management system

In this paper, we present an extensible, uniform, behavioral query model and its languages for the TIGUKAT object management system [POS92]. The TIGUKAT model is purely behavioral in nature, supports full encapsulation of objects, defines a clear separation between primitive components such as types, classes, collections, behaviors, functions, etc., and incorporates a uniform semantics over objects which makes it a favorable basis for a query model. Queries are modeled as type and behavior extensions to the base object model, thus incorporating queries as an extensible part of the model itself. We present the framework of the complete query model definition that includes the extended types and behaviors, a formal object calculus with safety based on the evaluable class of queries, an equivalent object algebra, an SQL-like ad hoc query language for user-level querying and proof of its completeness.

TIGUKAT: An Object Model for Query and View Support in Object Database Systems

Object oriented computing is in uencing many areas of computer science including software en gineering user interfaces operating systems programming languages and database systems The appeal of object orientation is attributed to its higher levels of abstraction for modeling real world concepts its support for incremental development and its potential for interoperability Despite many advances object oriented computing is still in its infancy and a universally acceptable def inition of an object oriented data model is virtually nonexistent although some standardization e orts are underway This report presents the TIGUKAT object model de nition that is the result of an investigation of object oriented modeling features which are common among earlier proposals along with some distinctive qualities that extend the power and expressibility of this model beyond others The literature recognizes two perspectives of an object model the structural view and the behavioral view Most object oriented formalisms have concentrated on one or the other of these two perceptions The TIGUKAT object model i favors formal speci cations for both the behavioral and structural components and ii shows an integration of the two components into a complete model de nition Furthermore the model emphasizes iii a clean separation and precise de nition of object modeling features which are usually bundled and only intuitively de ned in other models and iv a uniform approach to object modeling which encompasses all information including meta data as objects within the primitive de nitions The establishment of a formal object model provides a theoretical foundation from which inves tigations of other object database features will be pursued The rst of these involves the de nition of an object query model with complete calculus and algebra speci cations including an equiv alence transformation proof between the two Based on the query model object views and view management with update semantics will be examined The intention is to incorporate very powerful and dynamic object de nition and manipulation language features into the model In parallel with this a dynamic schema evolution policy will be developed for integrating new types into the model We are currently in the process of implementing the model presented in this report to establish a workable software base with the long range goal of developing a full featured object database management system TIGUKAT tee goo kat is a term in the language of the Canadian Inuit people meaning objects The Canadian Inuits commonly known as Eskimos are native to Canada with an ancestry originating in the Arctic regions of the country

Change Propagation in an Axiomatic Model of Schema Evolution for Objectbase Management Systems

Schema evolution is an important component of advanced information systems such as objectbase management systems. These systems typically support volatile and complex application domains that include engineering design, CAD/CAM, multimedia, and geo-information systems. The schema of these applications must be able to evolve along with the changing environment. There are two problems to consider in schema evolution: (i) semantics of change and (ii) change propagation. The first deals with the effects of the schema change on the overall type system. For example, the deletion of a property in a type affects the subtypes inheriting that property. Our previous work has introduced a sound and complete axiomatic model to deal with the semantics of change problem. The second problem deals with the techniques for propagating schema changes to the underlying objects. For example, the addition of an attribute to a type requires additional memory to be allocated to the objects so that values for the attribute may be stored. The first step of change propagation is to identify the affected objects. Subsequent steps carry out the actual changes. This paper deals with the first step by extending the axiomatic model with semantics to determine a sound and complete set of objects affected by a schema change. The extended model can be used with any method for carrying out the changes such as the conversion, screening, and filtering approaches proposed in the literature.

WWW in DSM: collaborative caching on the Web

The World Wide Web (WWW) is a large distributed system consisting of multiple servers and clients. The paper briefly describes a model called WWW in DSM that provides a collaborative cache through an underlying distributed shared memory (DSM) paradigm. The model allows sharing of retrieved documents among browsers using the DSM. The authors have implemented a prototype system that shares documents among browsers in a local network, in an intranet, and across the Internet.