Neil Coburn

A distributed system architecture for a distributed application environment

Advances in communications technology, development of powerful desktop workstations, and increased user demands for sophisticated applications are rapidly changing computing from a traditional centralized model to a distributed one. The tools and services for supporting the design, development, deployment, and management of applications in such an environment must change as well. This paper is concerned with the architecture and framework of services required to support distributed applications through this evolution to new environments. In particular, the paper outlines our rationale for a peer-to-peer view of distributed systems, presents motivation for our research directions, describes an architecture, and reports on some preliminary experiences with a prototype system.

The CORDS multidatabase project

In virtually every organization, data are stored in a variety of ways and managed by different database and file systems. Applications requiring data from multiple sources must recognize and deal with the specifics of each data source and must also perform any necessary data integration. The objective of a multidatabase system is to provide application developers and end users with an integrated view of and a uniform interface to all the required data. The view and the interface should be independent of where the data are stored and how the data are managed. CORDS is a research project focused on distributed applications. As part of this project, we are designing and prototyping a multidatabase system. This paper provides an overview of the system architecture and describes the approaches taken in the following areas: management of catalog information, schema integration, global query optimization, (distributed) transaction management, and interactions with component data sources. The prototype system gives application developers a view of a single relational database system. Currently supported component data sources include several relational database systems, a hierarchical database system, and a network database system.

Path constraints for graph-based data models: Towards a unified theory of typing constraints, equations, and functional dependencies

Virtually all semantic or object-oriented data models assume objects have an identity separate from any of their parts. These models allow users to define complex object types in which property values may be any other objects. Often the query language allows a user to navigate from object to object by following a property value path. In this paper, we consider the combination of three forms of constraints over complex object types: equations, functional dependencies, and typing constraints. The constraints are novel since component attributes may correspond to property paths instead of single properties. The kind of equational constraint we consider is also important: it abstracts the class of conjunctive queries for query languages that support property value navigation. Our form of typing constraint is novel for two reasons: it allows us to characterize well-formedness conditions on constraints in more appropriate semantic terms, and it can be used to support a form of molecular abstraction.

A logic for rule-based query optimization in graph-based data models

We present a wide-spectrum algebra and refinement calculus designed to allow one to reason about query optimization in graph-based data models.

A theory of specialization constraints for complex objects

Most semantic data models and object-oriented data models allow entity and object classes to be organized according to a generalization taxonomy. In addition, range restrictions (or property typing) may be specified not only on properties associated with a given class, but also on properties inherited from superclasses. In this paper, we consider a more general form of specialization constraint in which range restrictions are associated with property value paths, instead of with the properties themselves. One consequence is that the constraints enable a form of molecular abstraction, in which the internals of more complicated objects can be defined in terms of a collection of more primitive types. Sound and complete axiomatizations are given for two models: one not assuming a most specialized class rule (MSC), and another satisfying MSC together with an additional almost lower semilattice condition. Efficient decision procedures for both cases are also presented.