epub3                                  epub2
   metadata                               metadata
+     identifier                       +     identifier
?        id                            ?        id
?m       identifier-type
?m       scheme                        ?        scheme
+     title                            +     title
?        lang                          ?        lang
?m       title-type
?m       display-seq
+     language                         +     language
*     contributor                      *     contributor
?m       role                          ?        role
?m       file-as                       ?        file-as
?m       display-seq
*     creator                          *     creator
?m       role                          ?        role
?m       file-as                       ?        file-as
?m       display-seq
?     date                             *     date
      [simpler than it used to be 1]   ?        event
 m    modified [this one is special 2]
?     source                           *     source
?     type                             *     type
*     coverage                         *     coverage
*     description                      *     description
*     format                           *     format
*     publisher                        *     publisher
*     relation                         *     relation
*     rights                           *     rights
*     subject                          *     subject

[1] date is simpler than it used to be, I believe it means "when this book was originally written or created", and looks like this:

   <dc:date>2012</dc:date>

[2] modified metadata looks like this:

   <meta property="dcterms:modified">2011-01-01T12:00:00Z</meta>