“There are times when metadata created using one standard will need to be transformed or crosswalked to another standard so that metadata can been shared between systems.”
Crosswalking can be tricky business, but there can be no “metadata schema to rule them all” since there are too many different systems and different contexts for which metadata is used. In most cases, it should be possible to convert a record to a different standard fairly well. It can be possible to lose data however, if there is no equivalent field in another schema, or if detailed schema needs to be simplified. These three records of the same dataset were provided for comparison: 1, 2, 3
While they all describe the same resource, they each do it in a slightly different way. Fields like title, contributor/credit and abstract/description convert fairly directly – though the original record has also has a “short title” which is not included in the other records. “Geographic keywords” (a specific kind of subject field) is translated to the more general “keyword” section on the other two, along with other non-geographic keywords that aren’t actually supplied in the original record. So it’s clear that they’ve done more than just appropriating the content of the original to its closest equivalent in the other schema. Some original metadata has been created.