This is a "Hello World" example that shows how to use ODB to perform basic
database operations, such as making objects persistent, loading, updating
and deleting persistent objects, as well as querying the database for
objects matching a certain criteria.

The example consists of the following files:

person.hxx
  Header file defining the 'person' persistent class.

person-odb.hxx
person-odb.ixx
person-odb.cxx 
person.sql
  The first three files contain the database support code and the last file
  contains the database schema for the person.hxx header.

  These files are generated by the ODB compiler from person.hxx using the
  following command line:

  odb -d <database> --generate-query --generate-schema person.hxx
  
  Where <database> stands for the database system we are using, for example,
  'mysql'.

database.hxx
  Contains the create_database() function which instantiates the concrete
  database class corresponding to the database system we are using.

driver.cxx
  Driver for the example. It includes the person.hxx and person-odb.hxx
  headers to gain access to the persistent classes and their database support
  code. It also includes database.hxx for the create_database() function
  declaration.
    
  In main() the driver first calls create_database() to obtain the database
  instance. Then it executes a number of database transactions on persistent
  objects.

To run the example we first need to create the database schema. Using MySQL
as an example, this can be achieved with the following command:

mysql --user=odb_test --database=odb_test < person.sql

Here we use 'odb_test' as the database login and also 'odb_test' as the
database name.

Once the database schema is ready, we can run the example (using MySQL as
the database):

./driver --user odb_test --database odb_test