I don't think that this is what the guidelines say.
is used (I have supplied the missing terminal quotation marks). Here authorityURI points to the authority itself and valueURI to the value according to the same authority. This also agrees with the definition given above that an authorityURI is a "URI uniquely identifying the vocabulary from which the controlled term has been selected," whereas a valueURI is a "URI uniquely identifying the term or controlled value from a vocabulary." This could have been expressed more clearly, but there is no difference here between a term or a value.
Of course, duplicating "http//id.loc.gov/authorities
" is quite verbose, but while we can reason from the valueURI to the authority scheme used in it, this is not possible for a computer.
Hope this help you, As you know the attribute authority may be used to indicate that an element (title, name, etc.) is controlled by a record in an authority file (e.g. authority="naf"). In version 3.3, if you wanted to link the element to an authority list you must use this form "authority="???" xlink:href=" (e. g. <titleInfo type="uniform" authority="naf" xlink:href="http://www.loc.gov/sru-lccn/?query=n 93028706">). The attributes authorityURI and valueURI have been added to MODS from version 3.4, I think instead of this form and based on the linked data approach.But their difference, when you use an authority list (like LCSH, NAF, MeSH, ...) you should use authorityURI, and when you use a value list (like Relators and Roles, MARC Form of Item Term List, MARC Genre Term List
, ...) you should use valueURI. Because there are differences between the authority lists and the value lists.