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Dissertation Information for Rajiv Mohan Dewan

NAME:
- Rajiv Mohan Dewan

DEGREE:
- Ph.D.

DISCIPLINE:
- Computer Science

SCHOOL:
- University of Rochester (USA) (1986)

ADVISORS:
- None

COMMITTEE MEMBERS:
- None

MPACT Status: Incomplete - Not_Inspected

Title: ON COMBINED LOGICAL AND PHYSICAL DESIGN OF DATABASES

Abstract: In the conventional approach to database design, the design task is dichotomized into separate logical and physical design tasks. Because of this dichotomy, numerous tradeoffs are ignored. This dissertation studies the combined logical and physical database design problem. To provide a framework for analysis, the combined problem is formulated as an integer mathematical program. To evaluate a logical schema, physical characteristics and transaction implementation procedures have to be chosen such that the total operational costs, given the logical schema, are minimized. The logical schema that satisfies constraints that arise from user semantics and has minimum cost is chosen. This model provides new insights into the problem. It is shown that the set of relations used by a query, in the optimal solution, is a superset of set of relations required to satisfy the 'logical' data requirements alone. The 'extra' relations serve to reduce the cost of answering the query. The problem and its epsilon-approximation are shown to be NP-Hard. The formulation is very complex, and hence the problem is studied in a variety of restricted settings wherein the problem is greatly simplified. One of them, the problem of generating a denormalized schema and its physical characteristics, is considered for databases that have a high ratio of query activity to updates. Solution methods for the denormalized schema selection problem are developed. Experiments show the effect of data redundancy characteristics, transaction relative frequency and availability of secondary indexing on the optimal conceptual relational schema. In many cases, the best schema found is not in the Normal Form.

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