Don't look to a non-technical dictionary (esp. an en-gb one :) for
definitions of jargon.
Schema: representation of a data model in some canonical form. A set
of rules for how data are are allowed to be arranged in a datastore. An
SGML DTD is an example of a schema for SGML documents.
Scheme: A context in which to place a datum that allows its syntax (form)
and semantics (meaning) to be fully understood, processed and
interchanged.
Name Space: A (usually heirarchical) division of a logical terrain
instantiated physically as unique, labelled partitions.
DNS (Domain Name Service) manages a distributed namespace in that it
divides the universe of hostnames on the internet into managable
partitions known as domains. Instead of having to look up a host named
"metadatalistserver" as a peer of a billion other networked hosts (very
expensive and difficult to distribute and manage) the DNS makes us place
that machine into a name space (first .uk, then .ac, then .lut and finally
mrrl) so it can rule out the vast majority of other hosts and facilitate
speedier lookup. MIME (Multimedia Internet Mail Extensions) or Internet
Media Types are another example of a namespace, but this one is much
smaller than the DNS and is not distributed but centrally managed at the
ISI.edu.
The application of schemes in a name space to DC would be to allow
subject-domains to manage their own specialty schemes for elements like
SUBJECT without duplicating names or prefixes in the namespace that might
lead to namespace collisions.
Schemas describe data model for the 15 elements, their contents, qualfiers
and how subelements and their what falls under them (recursive
descendents?) will work.
-marc
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