图灵奖得主James.Gray关于SQL99研究资料

GuyDeng

All China Database Union

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2021-01-10

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Foreword

Jim Gray

Microsoft Research

In the last decade, SQL has evolved from the pure-relational model to a post-

relational model. This book is a lucid explanation of that evolution. At its core,

the old SQL is tables-of-rows-and-columns. The new SQL adds typed-tables, each

containing a set of objects accessed via methods. This is an enormous advance

in the utility and applicability of the SQL languagemand it goes a long way

toward reducing the impedance mismatch between databases and programming

languages.

SQL's new object model is the basis of the extensions to text, spatial, image

and data mining data types and methods. SQL has also grown to support OLAP

(on-line analytic processing) operations and functions, as well as better integra-

tion with Java, and to have cleaner support for data links (external files as values)

and data wrappers (foreign data sources).

All these changes are documented in the SQL standards. Unfortunately, those

standards are written by language lawyers and are very difficult to read. Fortu-

nately, Jim Melton, who is the editor of the SQL:1999 standard (and the SQL-92

standard), is also able to write lucid descriptions that most of us can read. Jim

wrote a previous volume that explained the "classical" aspects of SQL:1999: the

table-row-column stuff. 1 This book explains the post-relational SQL:1999 aspects:

objects, links, wrappers, and OLAP. It also hints at the progress in the emerging

topics of XML, text, spatial, image, and data mining.

SQL must interoperate with almost all languages, it must be persistent, and it

has to worry about security and schema evolution. These are not issues that most

Jim Melton and Alan Simon,

SQL:1999mUnderstanding Relational Language Components

(San

Francisco: Morgan Kaufmann Publishers, 2002).

vii

viii Foreword

object-oriented systems need to address, but they are central to SQL. Conse-

quently, designing the SQL object model was a pioneering and extremely deli-

cate task. Melton does a wonderful job describing the issues the designers faced

and explaining why they chose the path they did. He gives one of the more

insightful discussions of the concepts and issues that underlie object models. In

the end, you come away understanding the tradeoffs the designers made and

have a clear understanding of the final design. The result is quite elegant.

The SQL:1999 standard will influence commercial products for years to come.

This book is an excellent guidepost for features that products will likely add in

the future. It also gives a vendor-neutral and very readable view of the SQL lan-

guage. Hence, the book will be an indispensable reference both for expert SQL

users and for SQL implementers.

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