Possible metadata implementations (already available or planed in a future Geotools version) are:
{@link org.geotools.metadata.iso}: concrete implementation of ISO interfaces, including ISO 19115.
{@code org.geotools.metadata.dublin}: concrete implementation of Dublin core interfaces. Not yet implemented.
{@link org.geotools.metadata.sql}: implementation of metadata interfaces backed by a SQL database. The metadata interfaces doesn't need to be ISO ones, which is why this package is not a sub-package of the ISO's one.
{@code org.geotools.metadata.xml}: implementation of metadata interfaces backed by a XML files. The metadata interfaces doesn't need to be ISO ones, which is why this package is not a sub-package of the ISO's one. Not yet implemented.