Redmine

Hi ,
We need to integrate Redmine project with TFS for a particular project.
We are analysing the Redmine database Schema for the relationships between issues,users,comments and Journals and are referencing the attached diagram.

Had a question as to how a journal item can be linked to an issue? as according to the diagram it is only linked to a user id.
Would appreciate if some one can throw some light as to how an issue can be related to a Journal.

Regards,
KG