Impossible Data Warehouse Situations: Solutions from the Experts [Paperback]

In the seminars, presentations, and classes we teach on data warehousing, we are often subjected to what appear to be "impossible situations.However, they do have solutions, and that's what this book is all about.

We took the 91 impossible situations discussed in this book from our classes, from the DM Review "Ask the Experts" forum, from data warehouse consultants, and from colleagues in the field who have experienced these situations. These are all real situations, but we have disguised them to protect the authors as well as to protect the organizations experiencing the situations from the attendant shame and humiliation. As a side note, reviewers of specific situations in our manuscript were quick to say, "I know what company this describes," and they were almost always wrong.

There is no reason that each organization, as it begins and continues to develop data warehouse projects, must wrestle with many of the very difficult situations that have confounded other organizations. The same impossible situations continue to raise their ugly heads, often with surprisingly little relation to the industry, the size of the organization, or the organizational structure. In this book we let you know you are not alone and your problems are not unique. We also offer hope to the perplexed who see no obvious solutions to their problems.

Some of the situations should resonate with those of you planning to enhance your data warehouse by adding new data, additional users, or new applications. It may be that the impossible situation has not yet emerged, but you definitely see it just around the bend. After reading this book, you should be able to avoid the situation rather than needing to fix it after it has developed.

Every stakeholder, data warehouse architect, data warehouse project manager, and user liaison responsible for any portion of a data warehouse faces the challenges identified in these pages. These people are looking for solutions to situations that, at first, appear to have no possible answer.

This book does not present an introduction to data warehousing. To benefit most from this book, you should have some level of familiarity with data warehousing through practical experience, conferences, or previous reading of data warehouse texts. This book is also not geared to any primary topic such as meta data or data quality; instead, it covers a broad range of areas. The reference section lists both introductory and more advanced suggested reading material.

User liaisons and managers may wish to read only Part I (Impossible Management Situations). All others will want to read both Part I and Part II (Impossible Technical Situations).

As mentioned, the first part of the book deals with managerial situations and the second part with technical situations. The order within these sections is very roughly the order in which projects are developed and situations are encountered, but each chapter stands alone without depending on those that precede it. You can read the book from front to back, but more likely you will be drawn to the chapters describing the problems that cause you the most pain. For example, if you struggle with data quality issues, Chapter 11, Data Quality, is the place to start. Each subsection of a chapter presents a different impossible situation related to the chapter's topic, followed by the experts' suggested solutions (presented in the alphabetical order of the experts' last names).

The Data Warehouse Glossary at the back of the book clarifies some terms and helps keep you from going down the wrong path. Misunderstanding the terminology used in this fast-changing field has caused significant misinterpretation that has resulted in wasted time and money, dissension, and hurt feelings. The Data Warehouse Glossary contains acronyms as well as data warehouse and information technology terms. A few of these have more than one definition. Please refer to the definitions to avoid any misunderstandings as you read through the situations and solutions. If your native language is not English, you will find the Colloquialism Glossary useful since the experts used many colloquial expressions in their contributions to this book.

You will notice strong biases in the experts' responses. The experts came to these dearly held opinions honestly through extensive experience in real-world situations. A few of the answers are embarrassingly similar, while some sharply disagree, appearing to contradict each other. Recognizing that there is usually more than one answer to every problem, very much depending on the organization and the situation, we made no attempt to reconcile the differences. We trust you will astutely choose the solution that will work best in your organization.

The following people contributed their expertise to address the situations we present in this book:

• Sid Adelman
• Joyce Bischoff
• Jill Dyche
• Douglas Hackney
• Sean Ivoghli
• Chuck Kelley
• David Marco
• Larissa Moss
• Clay Rehm

True experts, these men and women have worked in the data warehouse arena for a cumulative 142 years. If anyone can address these impossible situations, they can.

The experts suggested best practices based on their experiences with both successful and unsuccessful implementations. The experts correctly identified many of the situations as reflecting the symptoms of a dysfunctional organization, knowing that without understanding the real causes, no effective solution could be honestly recommended. When presented with insufficient information, the experts resorted to making assumptions about the situations.

The experts' bios appear in the back of the book.

A number of impossible situations came to our attention after the experts received the original batch of 91 situations, and we all feel sure more will appear. If you want to contribute a new situation for consideration, please send it to impossibles@sidadelman.com. We may include your situation in a second edition of this book.

The situations in this book were gleaned from a variety of sources. A major source was my Data Warehouse Project Management Seminar, in which students would present seemingly impossible situations. I'd like to thank all the students in this seminar who were brave enough to expose their extremely difficult if not impossible situations.

My clients, my colleagues, and the experts represented in this book contributed many of the other situations. There are no attributions for the impossible situations themselves. This was intentional to protect the reputations and careers of those who submitted them.

A number of situations were pulled from submissions to DM Review's "Ask the Experts" forum, mentioned earlier. My thanks to the publishers of DM Review who allowed us to use those submissions and to Mary Jo Nott, the Web Editor at DM Review who manages the forum.

This book is a compilation of hard-won wisdom from the experts—my colleagues I've been privileged to know and work with. As you will see in their solutions, there would not have been a book without their insightful contributions. Thanks especially to Larissa Moss and Joyce Bischoff for their excellent ideas and suggestions that went well beyond their expert solutions.

Thanks also go to the original reviewers who made excellent suggestions about ways to improve the book and make it more readable and informative. Thanks to Jean Schauer, Editor in Chief of DM Review; Majid Abai, President of Seena Technologies; and Dennis Fitzpatrick. I also thank Lou Russell and Cort Pahl for their ideas and insights.

Anyone who has written a book knows the work and expertise of the various editors. I salute the editing savvy of the folks at Addison-Wesley, including Mary O'Brien, Alicia Carey, and Simone Payment. Steven King in On Writing wrote that your editor is always right. This was especially true for this book. Special thanks to my copyeditor, Chrysta Meadowbrooke.

If you are actually reading this book, it's due to the marketing skills of Curt Johnson and Chanda Leary-Coutu.

Any finally thanks to Sisyphus who graces the book's cover for being the model for all those who believe their role in this difficult data warehousing environment is an uphill struggle with no solution in sight.