DataTypes in schema.org

Hi colleagues,
This is probably old discussions but probably someone can help me to 
understand why the schema.org accepts  plein-Literal where sxd dataType 
were expected? This for all DataTypes ?.
Predicates like schema:birthDate , schema:startDate etc we expected as 
object xsd:date but we have a string literal. Which is handicap for use of 
those predicate in semantic web. Actually with plein-literal we can use 
whatever in the quotes.
Can someone help me to see clear there?
Additionally is it true that schema.org accepts strings where objects were 
expected?

Kind Regards,

Marc Twagirumukiza | Agfa HealthCare
Senior Clinical Researcher | HE/Advanced Clinical Applications Research
T  +32 3444 8188 | M  +32 499 713 300

http://www.agfahealthcare.com
http://blog.agfahealthcare.com
Click on link to read important disclaimer: 
http://www.agfahealthcare.com/maildisclaimer