anymore if DVDs are added).

Complete PrintType (set to BOOK). Added DVD as PrintType where
appropriate.

number of updated publication attributes.

We distinguish between errors and warnings. Warnings are emitted
if the same industrial identifier has multiple publications.
All other problems are treated as errors. Errors have priority over
warnings. All issue messages (errors and warnings) are concatenated
to the exception message.

Added comments.

Emit warning if necessary.

and only then throw an exception. Previously we threw one after the
very first error.

Throw exception in case a book cannot be found.

Use JacksonFactory.getDefaultInstance() instead of new factory.

Removed debugging output.

Important note: do not use quotes for the key

without success so far.

retrieved from the Google Books API.

This list is partial (only about half of the books are
entered) and incomplete (in many cases only the ISBN
is available).

business objects to fail. Replaced arrays by Lists.

This directory is needed by Eclipse to build the software. It is automatically generated by 'mvn install'. Yet, if a programmer does not run maven on the console, the build in Eclipse will fail. Hence, we need to check in this directory. Yet, Git does not allow one to check in empty directories (it administers only files). Hence, we create an empty .gitignore file here.