Hello Hugh,
first of all, there is no reason why LRMI isBasedOnUrl (as it is
currently called, though that may change) should make a unique
contribution over and above DC terms. LRMI properties were designed
to supplement *
schema.org* to enable the description of learning
resources. If there were terms useful for describing educational
properties and relationships in the DC namespace that were not part
of
schema.org, then they were candidates for being included in LRMI.
Of course, there are differences in approach between and history
between
schema.org and DC which mean that they might not look the
same once they get there.
That said, the answer to your question is:
The use case for isBasedOnUrl was that very often open educational
resources are repurposed before being reused. For example, I, in the
UK, may take a resource which compares rainfall between US cities
(Seattle and Utah) and change it to make reference to UK cities
(Manchester and Norwich) and therefore more suitable for my
students. isBasedOnUrl allows me to express the relationship between
my resource and the original.
Looking at the the DC terms you mention:
* hasPart, isPartOf: no, being based on a resource is not the same
as being part of it (and
schema.org has
http://schema.org/hasPart
and
http://schema.org/isPartOf)
* isFormatOf / hasFormat: no, this would do for changing a Word file
to PDF, but that's not a substantive change (and
schema.org has
http://schema.org/encoding which can be used for this)
* hasVersion: yes, in the sense that this links to "A related
resource that is a version, edition, or adaptation of the described
resource"-- isBasedOnUrl covers the 'adaptation of the described
reasource.' Schema.org has
http://schema.org/workExample /
http://schema.org/workExample which covers some of the same ground
as hasVersion
Hope this helps, Phil