Preface to the Second Edition

This second edition of Tale of Two Systems comprises an update of the original text. Several factors compelled this update:

• Quite a few of the links in the original text had become invalidated. Some of these could simply be updated, but others were pointing to places which have disappeared since the publication of the first edition of this text. The locations in the text where that applied had to be accordingly modified.
• Some of the places on the web which in the first edition were suggested as good places to practice and run coding exercises have disappeared.
• Some of the first-edition exercises can no longer be run on these public places because of security reasons.
• The first edition contained exercises in C# and PHP and used both RavenDB and MongoDB for NoSQL exercises. Not only does maintenance of instructions for each of these constitute quite a bit of work, but students of the text had to install and work with multiple platforms. Hence, we decided to change all exercises to use only Python and MongoDB.
• One of the appendices was removed and its contents integrated in one of the regular chapters.
• A new exercise was added to Chapter 2.
• A chapter on a recently added tool —The NGSS Explorer— and its architecture was added.
• A large number of editorial changes were made.
• References to new tools and texts were added.