Foreword by Michael J. Carey, Ph. D., UC Irvine It is a pleasure to introduce this new book by Don Chamberlin, as I have known Don for many years and his writings are always exceptional. I first came to know Don personally during several sabbatical visits from the University of Wisconsin to the database research group at IBM Almaden Research Center. I later had the pleasure of working with Don as an IBM colleague on object-relational extensions to SQL (SQL: 1999 and SQL: 2003) and to DB2, and later still on XQuery, the W3C query language standard for XML data, when I was doing information integration work at BEA Systems and he was representing IBM Research center in San Jose, in the brave new world of XML and XML queries. My experience with Don is that, in addition to being way too modest for someone who is the IBM Fellow who co-invented SQL and the world’s leading expert on query language design, he asks tough questions that get to the heart of problems, illustrates things in the clearest possible terms using insightful examples, and has a way of explaining things to make them readily accessible to readers at all levels. In my opinion, Don’s book “A Complete Guide to DB2 Universal Database” from the 1990s was, and still is, one of the best books ever written for someone who wants to learn about SQL and its realization in IBM’s DB2 system for Unix-and Windows-based platforms.

In my role as a part-time consultant to Couchbase, Inc., I was excited when another chance to work with Don came about: Don’s interest in query languages somehow landed him at an early Couchbase seminar on the first version of N1QL, an SQL-inspired language for JSON data, and he became intrigued. Meanwhile, my work as an architect for Apache AsterixDB and Couchbase Analytics put me in a position to be intrigued by SQL++, a SQL for JSON query language initially designed by Yannis Papakonstantinou and students at University of California, San Diego. I was beginning to tire of trying to convince our AsterixDB users that its initial query language (AQL, inspired by XQuery) was what they should really want for semi-structured data, Yannis had a thoughtfully designed alternative (and Couchbase was working with UCSD on N1QL), and Don was freshly retired from IBM but not from thinking about query language design. We joined forces and, together with some technical leads at Couchbase and elsewhere, SQL++ has been refined into a potential standard for querying JSON and JSON-like data.