You are completely right. It was missing "tomcat" cookbook in the type attribute of the databag.
Everything worked fine excepto with the tomcat cookbook. The process of starting tomcat gives back the following error.
[Thu, 12 Apr 2012 12:18:34 +0200] DEBUG: service[tomcat] runlevel 5, action start, priority 92
[Thu, 12 Apr 2012 12:18:34 +0200] DEBUG: Executing /usr/sbin/invoke-rc.d tomcat6 start
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: ---- Begin output of /usr/sbin/invoke-rc.d tomcat6 start ----
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: STDOUT: * Starting Tomcat servlet engine tomcat6
...fail!
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: STDERR: invoke-rc.d: initscript tomcat6, action "start" failed.
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: ---- End output of /usr/sbin/invoke-rc.d tomcat6 start ----
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: Ran /usr/sbin/invoke-rc.d tomcat6 start returned 1
[Thu, 12 Apr 2012 12:18:39 +0200] ERROR: service[tomcat] (tomcat::default line 42) has had an error
[Thu, 12 Apr 2012 12:18:39 +0200] ERROR: service[tomcat] (/var/cache/chef/cookbooks/tomcat/recipes/default.rb:42:in `from_file') had an error:
service[tomcat] (tomcat::default line 42) had an error: Chef::Exceptions::Exec: /usr/sbin/invoke-rc.d tomcat6 start returned 1, expected 0
---- Begin output of /usr/sbin/invoke-rc.d tomcat6 start ----
STDOUT: * Starting Tomcat servlet engine tomcat6
...fail!STDERR: invoke-rc.d: initscript tomcat6, action "start" failed.
---- End output of /usr/sbin/invoke-rc.d tomcat6 start ----
/usr/lib/ruby/vendor_ruby/chef/mixin/command.rb:127:in `handle_command_failures'
/usr/lib/ruby/vendor_ruby/chef/mixin/command.rb:74:in `run_command'
/usr/lib/ruby/vendor_ruby/chef/provider/service/init.rb:37:in `start_service'
/usr/lib/ruby/vendor_ruby/chef/provider/service.rb:57:in `action_start'
/usr/lib/ruby/vendor_ruby/chef/resource.rb:440:in `send'
/usr/lib/ruby/vendor_ruby/chef/resource.rb:440:in `run_action'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:45:in `run_action'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `converge'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `each'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `converge'
/usr/lib/ruby/vendor_ruby/chef/resource_collection.rb:94:in `execute_each_resource'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:116:in `call'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:116:in `call_iterator_block'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:85:in `step'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:104:in `iterate'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:55:in `each_with_index'
/usr/lib/ruby/vendor_ruby/chef/resource_collection.rb:92:in `execute_each_resource'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:76:in `converge'
/usr/lib/ruby/vendor_ruby/chef/client.rb:312:in `converge'
/usr/lib/ruby/vendor_ruby/chef/client.rb:160:in `run'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:239:in `run_application'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:229:in `loop'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:229:in `run_application'
/usr/lib/ruby/vendor_ruby/chef/application.rb:67:in `run'
/usr/bin/chef-client:25
[Thu, 12 Apr 2012 12:18:39 +0200] ERROR: Running exception handlers
[Thu, 12 Apr 2012 12:18:39 +0200] FATAL: Saving node information to /var/cache/chef/failed-run-data.json
[Thu, 12 Apr 2012 12:18:39 +0200] ERROR: Exception handlers complete
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: Re-raising exception: Chef::Exceptions::Exec - service[tomcat] (tomcat::default line 42) had an error: Chef::Exceptions::Exec: /usr/sbin/invoke-rc.d tomcat6 start returned 1, expected 0
---- Begin output of /usr/sbin/invoke-rc.d tomcat6 start ----
STDOUT: * Starting Tomcat servlet engine tomcat6
...fail!STDERR: invoke-rc.d: initscript tomcat6, action "start" failed.
---- End output of /usr/sbin/invoke-rc.d tomcat6 start ----
/usr/lib/ruby/vendor_ruby/chef/mixin/command.rb:127:in `handle_command_failures'
/usr/lib/ruby/vendor_ruby/chef/mixin/command.rb:74:in `run_command'
/usr/lib/ruby/vendor_ruby/chef/provider/service/init.rb:37:in `start_service'
/usr/lib/ruby/vendor_ruby/chef/provider/service.rb:57:in `action_start'
/usr/lib/ruby/vendor_ruby/chef/resource.rb:440:in `send'
/usr/lib/ruby/vendor_ruby/chef/resource.rb:440:in `run_action'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:45:in `run_action'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `converge'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `each'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `converge'
/usr/lib/ruby/vendor_ruby/chef/resource_collection.rb:94:in `execute_each_resource'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:116:in `call'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:116:in `call_iterator_block'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:85:in `step'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:104:in `iterate'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:55:in `each_with_index'
/usr/lib/ruby/vendor_ruby/chef/resource_collection.rb:92:in `execute_each_resource'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:76:in `converge'
/usr/lib/ruby/vendor_ruby/chef/client.rb:312:in `converge'
/usr/lib/ruby/vendor_ruby/chef/client.rb:160:in `run'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:239:in `run_application'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:229:in `loop'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:229:in `run_application'
/usr/lib/ruby/vendor_ruby/chef/application.rb:67:in `run'
/usr/bin/chef-client:25
[Thu, 12 Apr 2012 12:18:39 +0200] FATAL: Stacktrace dumped to /var/cache/chef/chef-stacktrace.out
[Thu, 12 Apr 2012 12:18:39 +0200] DEBUG: Chef::Exceptions::Exec: service[tomcat] (tomcat::default line 42) had an error: Chef::Exceptions::Exec: /usr/sbin/invoke-rc.d tomcat6 start returned 1, expected 0
---- Begin output of /usr/sbin/invoke-rc.d tomcat6 start ----
STDOUT: * Starting Tomcat servlet engine tomcat6
...fail!STDERR: invoke-rc.d: initscript tomcat6, action "start" failed.
---- End output of /usr/sbin/invoke-rc.d tomcat6 start ----
/usr/lib/ruby/vendor_ruby/chef/mixin/command.rb:127:in `handle_command_failures'
/usr/lib/ruby/vendor_ruby/chef/mixin/command.rb:74:in `run_command'
/usr/lib/ruby/vendor_ruby/chef/provider/service/init.rb:37:in `start_service'
/usr/lib/ruby/vendor_ruby/chef/provider/service.rb:57:in `action_start'
/usr/lib/ruby/vendor_ruby/chef/resource.rb:440:in `send'
/usr/lib/ruby/vendor_ruby/chef/resource.rb:440:in `run_action'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:45:in `run_action'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `converge'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `each'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:81:in `converge'
/usr/lib/ruby/vendor_ruby/chef/resource_collection.rb:94:in `execute_each_resource'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:116:in `call'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:116:in `call_iterator_block'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:85:in `step'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:104:in `iterate'
/usr/lib/ruby/vendor_ruby/chef/resource_collection/stepable_iterator.rb:55:in `each_with_index'
/usr/lib/ruby/vendor_ruby/chef/resource_collection.rb:92:in `execute_each_resource'
/usr/lib/ruby/vendor_ruby/chef/runner.rb:76:in `converge'
/usr/lib/ruby/vendor_ruby/chef/client.rb:312:in `converge'
/usr/lib/ruby/vendor_ruby/chef/client.rb:160:in `run'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:239:in `run_application'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:229:in `loop'
/usr/lib/ruby/vendor_ruby/chef/application/client.rb:229:in `run_application'
/usr/lib/ruby/vendor_ruby/chef/application.rb:67:in `run'
/usr/bin/chef-client:25
[Thu, 12 Apr 2012 12:18:39 +0200] FATAL: Chef::Exceptions::Exec: service[tomcat] (tomcat::default line 42) had an error: Chef::Exceptions::Exec: /usr/sbin/invoke-rc.d tomcat6 start returned 1, expected 0
---- Begin output of /usr/sbin/invoke-rc.d tomcat6 start ----
STDOUT: * Starting Tomcat servlet engine tomcat6
...fail!STDERR: invoke-rc.d: initscript tomcat6, action "start" failed.
---- End output of /usr/sbin/invoke-rc.d tomcat6 start ----
However, the tomcat is up and running and the war application can be accessed at http://<ip>:8080/ since it is described in ROOT.xml