DC includes an element called "Date". You display it like this:
<meta name="dc.Date" content="2011-06-28" />
But the idea of qualifiers lets you have a "Date Created" and "Date Updated." But is there a way to embed this correctly? I've seen this a couple ways:
<meta name="dc.Date" content="(Scheme=Created) 2011-06-28" />
<meta name="dc.Date" content="2011-06-28" scheme="Created" />
Is there a standard?
As I read the spec these things you are talking about are Element Refinements (like created, modified, etc. for date).
Element Refinement: These qualifiers make the meaning of an element narrower or more specific. A refined element shares the meaning of the unqualified element, but with a more restricted scope. A client that does not understand a specific element refinement term should be able to ignore the qualifier and treat the metadata value as if it were an unqualified (broader) element. The definitions of element refinement terms for qualifiers must be publicly available.
from dublincore.org
The spec suggests two equivalent ways of writing:
<meta name="DC.Date.modified" content="2001-07-18" />
<meta name="DCTERMS.modified" content="2001-07-18" />
A Scheme that you mention is used to define encoding, formatting of data. For example for dates, it can either be DCMI Period or W3C-DTF as seen on this page.
Encoding Scheme: These qualifiers identify schemes that aid in the interpretation of an element value. These schemes include controlled vocabularies and formal notations or parsing rules. A value expressed using an encoding scheme will thus be a token selected from a controlled vocabulary (e.g., a term from a classification system or set of subject headings) or a string formatted in accordance with a formal notation (e.g., "2000-01-01" as the standard expression of a date). If an encoding scheme is not understood by a client or agent, the value may still be useful to a human reader. The definitive description of an encoding scheme for qualifiers must be clearly identified and available for public use.
from dublincore.org
They can be used like:
<meta name="DC.date" scheme="DCTERMS.W3CDTF" content="2001-07-18" />