Different names (and languages) for the same thing (journal_article vs SerialArticleWork)
Data
elements at different levels of speciality (title vs FullTitle,AlternativeTitle).
Different
allowed values for elements (pii vs not pii)
Data at
different levels of granularity (journal_article vs SerialArticleWork/SerialArticleVersion).
Data in
different structures
(article as attribute of journal or vice versa).
Data from
different sources
(local codes vs ONIX codes).
Contextual
meaning (DOI of
what
?)
Different
representation (1
title vs n titles).
Different
mandatory requirements
(ISSN mandatory vs optional).
Schemas are
being updated all the time.
All this is tricky one-to-one.
Many-to-many it is a nightmare.
A common,
structured, Data Dictionary can solve the problem
Indecs (and
subsequent development) has done so: now used by DOI