MODELS OF INFORMATION: THE FEASIBILITY OF MEASURING THE STABILITY OF DATA MODELS Myron Murray Marche London School of Economics and Political Science Submitted in fulfilment of the requirements for the award of the degree of Doctor of Philosophy of the University of London LONDON, ENGLAND SUMMER, 1991 UMI Number: U061829 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U061829 Published by ProQuest LLC 2014. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT The theory of data modelling makes a variety of claims about schema stability. This research determined the current state of data modelling practice, and tested hypotheses related to measuring model stability. The research developed a method whereby the major elements of a data model can be consistently represented whatever process was originally used for modelling. This was achieved through a construction of a logical relational schema from the record design. The construction/reconstruction process attempted to identify the primary meaning primitives of a data model in order to track changes to them in different iterations of the application. The stability data collection process was applied to a case study followed by a series of models to generate further data. The early evidence indicated that data model instability has it roots in errors in modelling, errors in the semantic analysis whether done consciously or intuitively, and in changes to the requirements brought on by changes to the "reality". This research suggested that some of the elements of a data model are significantly more important than others. The research documented problems associated with the transformation of natural language into the constraints of data dictionaries. This exploration into the potential application of linguistic research into systems theory and practice identified a number of theoretically interesting problems, such as variable semantic determination. The discussion outlined some specific techniques an analyst can use to improve the process of semantic analysis. The work suggested that there should be greater concentration on the question of data model evolvability, and the appropriate preservation of meaning across model versions, and not necessarily on data model stability. To Michael, Stephen, and Janet ACKNOWLEDGEMENTS While there is only one name on the title page of this work, there can be no question that it exists only due to the effort of many people. I must first acknowledge the original support of Professor Ronald Stamper, who encouraged me to begin studies at the London School of Economics, and who was willing to let his students think in very broadest of terms. While beginnings are very important, endings are just as important, and often substantially more difficult. Coming to the end of the research was in no small measure due to the efforts of Dr Jonathan Liebenau who provided effective supervision over most of the life of this research, and this he did with sensitivity, unfailing good humour, and good grace. All systems professionals appreciate the importance of strong project management. I must thank the project manager for the data collection phase of this work, Mr. Ian Cameron, who in his typical fashion did not take no for an answer. The encouragement and confidence of many friends, clients, and business associates is also gratefully acknowledged. I have invariably learned more from them than they have from me. My colleagues and friends at the London School of Economics have always made it a place for the best kind of open intellectual exploration. Thanks especially to Dr Jim Backhouse, and Professor Ian Angell. Finally, the love and support of my wife Janet, as well as the patience of my children, Michael and Stephen were instrumental in reaching this goal. Graduate schools should really award research degrees to families, not to individuals. TABLE OF CONTENTS PART I THE THEORY AND PRACTICE OF DATA MODELLING P reface....................................................................................................................... viii Chapter 1 - INTRODUCTION ................................................................................. 1 Chapter 2- THE INTELLECTUAL FOUNDATIONS OF DATA MODELLING....................................................................................... 5 A. The Roots of Data Modelling Theory ............................................... 6 B. T h e Philosophical Foundations of Data M odelling ............................................................................................ 12 1. Is Reality Subjective or is it Objective? .............................. 12 2. Semantics .................................................................................. 20 3. Schemas and Databases as Forms of Communication . 34 C. Data Modelling - Theory Into Practice ............................................ 39 Chapter 3 - A SURVEY OF DATA MODELLING PRACTICES IN CANADA ......................................................................................... 51 PART II - DEVELOPING AND APPLYING A TOOL FOR STABILITY MEASUREMENT Chapter 4 - DEVELOPING THE STABILITY MEASUREMENT TOOL . 62 A. What Do We Mean By Measurement? ............................................ 62 B. The Characteristic of Stability in a Data Model ................. •............................................................................. 64 1. The Literature is Not Specific in its References to Stability .................................................................................. 64 2. The Consequences of Instability .......................................... 69 C. The Data Model and Its Important Elements .................................. 71 1. Physical Database Design ................................................... 71 2. The Conceptual Data Model ................................................. 71 3. The Logical Data Model . ................................................. 73 4. Elements to a Data Model Which Might Be Important to Stability Measurement .................................................... 75 D. Creating the Data Collection Sheets for Model Changes 77 1. Creating the Attribute Data Collection Sheet .................... 78 2. Creating the Entity Data Collection Sheet ......................... 80 3. Creating the Relationship Data Sheet .................................. 81 4. Creating the Background and Model Summary Data Collection Sheet ................................................................... 82 TABLE OF CONTENTS (continued) Chapter 5 - A CASE STUDY OF THE TOOL IN U S E ...................................... 85 A. Introduction to the Case Study ............................................... 85 B. The Distribution of Office Space System ....................................... 86 C. The Space Recording and Control System (1) - October 1988 . 92 D. The Space Recording and Control System (2) - August, 1989 . 99 E. Analysis of the Case Study Results ........................................ 104 Chapter 6 - THE RESULTS OF THE SUMMARISED CASES ....................... 107 A. A Quantitative Assessment of the Models and Their Changes . 108 B. Qualitative C om m ents .............................................................. 115 C. Judging And Assessing the Performance of the Measurement Process ............................................................................................ 117 1. Summarising the Stability Measurement Process 117 2. Applying the Criteria of Measurement Effectiveness .. 119 PART III - TOWARDS A CRITICAL THEORY OF DATA MODELLING Chapter 7 - DATA MODELLING STABILITY, INSTABILITY, AND EVOLV ABILITY ............................................................... 123 A. General Observations From Applying the Measurement P rotocol ................................................................................ 124 B. Why Do Models Appear Stable at All? ...................................... 127 C. Stability Versus Evolvability in Data M odels ................. 131 Chapter 8- DATA MODELLING THEORY, PRACTICE, AND PROSPECTS .................................................................................. 135 A. Data Modelling - An Example of How It Is Practised .............. 135 1. An Initial Definition of Building Was Prepared ............ 139 2. Testing the Idea of Building, and Its Attributes 141 B. Learning From The Problems Of Data Modelling ......... 145 C. Hermeneutics And Semantic Analysis - Coming to the Meaning of T h in g s .............................................................................. 150 1. Hermeneutics - The Process of Interpretation ................. 151 2. The Prospects for Extending Semantic Analysis and Data Modelling ................................................................... 155 TABLE OF CONTENTS (continued) Chapter 9 - CONCLUSIONS AND FURTHER RESEARCH CONSIDERATIONS......................................................................... 165 A. General Summary of the Research ...................................... 165 B. Other Research