Page 183 - Building Digital Libraries

CHAPTER 7

Within organizations, metadata practices will change over time. Shifting
data models and formats have exacerbated this problem, as institutions
reevaluate data scope or migrate to new digital library systems. These types
of changes, while possibly advantageous within a local system, represent
barriers preventing an organization from participating in larger interoper-
ability efforts.

Schema Granularity
Very rarely does crosswalking occur between two metadata schemas that
share the same level of granularity. In part, this is due to the nature of
descriptive formats—they tend to be created to meet a specific need and
capture specific types of descriptive information. As a result, the crosswalk-
ing of metadata becomes a process of (1) deciphering how metadata ele-
ments are related, and (2) determining whether the crosswalk will result in
a loss of data granularity. In the best-case scenario, metadata crosswalkers
are looking for metadata elements that have one-to-one matches; that is, a
title in one schema that matches directly with the title element in another
schema so long as the granularity within the title elements is equal. In this
case, metadata can be directly mapped from one element to another. This
would be a lossless crosswalk—something really only achieved when mov-
ing data between MARC21XML and MARC. More likely, metadata cross-
walkers will need to deal with one-to-many and many-to-many matches.
This is where one metadata element in one schema matches the definition
of multiple metadata elements in a different schema; for example, moving
data between Dublin Core and MARC21. As noted in past chapters, Dublin
Core is a relatively low granular format utilizing only fifteen core metadata
elements. When crosswalking between Dublin Core and MARC, we see
a number of instances where a single Dublin Core field maps to multiple
MARC fields (see figure 7.4).
If we take a closer look at the Dublin Core creator field, we see very
clearly how granularity can affect metadata crosswalking. The Dublin Core
creator element, by definition, stores information relating to the publishers
of a work. This means that any individuals or organizations responsible for
the creation of the document should be tagged as a creator within the Dublin
Core schema. Within MARC21, entities are tagged according to the type of
entity (personal, corporate, etc.) and their relation to the work, that is, as
the main entry or contributor to a work. As such, the Dublin Core creator
element could theoretically map into one of seven different metadata ele-
ments within MARC21. What’s more, since Dublin Core doesn’t capture the

DUBLIN CORE MARC21
Creator 100, 110, 111, 700, 710, 711, 720

FIGURE 7.4
Dublin Core => MARC21 Author Crosswalk

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