Storing incomplete dates in database

[lfoppiano]

See #61 .
We need to look how it is done, as I've seen this problem already in different projects.

[lfoppiano]

Some links for inspiration:

• http://stackoverflow.com/questions/9134497/mysql-datatype-to-store-month-and-year-only
• http://stackoverflow.com/questions/6882788/store-incomplete-date-in-mysql-date-field

[Aazhar]

Actually , the benefit of OAI-PMH is to inform about the changing state of the repository, so instead of the publication date we should consider the modification date actually