Moving Between Standards (Crosswalking)
Crosswalks are human- or computer-readable documents that map metadata elementsIndividual instance of a metadata label and value pair. For example, "creator: John Doe" is a metadata element. Related Guide between different metadataData about data. Metadata provides a context for research findings, ideally in a machine-readable format. It enables discovery of data via an electronic interface, and correct use and attribution of findings. Related Guide standards.
Crosswalks can apply to content standardsA list or hierarchy of required metadata elements to be included in the metadata description. Related Guide, vocabulariesA set of terms (e.g., words) that are used in a specific community. Related Guide, or both. An automated crosswalk process may take an instanceA metadata document describing a resource in a standards-compliant manner For example, the Everglades Hydrology and Water Quality Data document provided in XML by the USGS. Also, see other MMI-provided metadata instance examples. of a metadata description that is presented in a particular format and change the format and element names and the valuesMetadata values are the content connected to metadata labels in a metadata element. For example, if the metadata label is "date", the metadata value could be "May 13, 2007". Related Guide within those elements (i.e., the vocabulary) to meet the requirements of the second standard.
Crosswalking is generally done when datasets using different metadata standards or vocabularies need to be integrated. For example, consider a website providing a searchable metadata directory. If the different datasets composing the directory were described using different standards and vocabularies, it would be difficult for a user to search across them effectively.
If someone was interested in wave height data, she might need to know to search for “wave ht (m)” in one dataset and “wave amplitude” in another. A crosswalk that defined these two elements as synonymous would allow a website to be constructed that allowed the user to search on either term, and retrieve applicable results from both datasets.
Due to the complexity of metadata content standards, there are few automated processes to crosswalk between content standards. Even in those cases where automated crosswalks exist, inevitably some information is lost when crosswalks are made. This is due to the complexity of the standards and potentially non-overlapping subject areas. When there are subject areas that do not overlap, even manual translation between standards does not result in complete information transfer.
The Crosswalk Process
The process of mapping between content standards or vocabularies is usually divided into the following steps: harmonization, semantic mappings, rules, and transformation. These are described in the next guide.
Suggested Citation
Graybeal, J., Isenor, A., Wang, H. 2009. "Moving Between Standards (Crosswalking)." In The MMIMarine Metadata Interoperability Guides: Navigating the World of Marine Metadata. http://marinemetadata.org/guides/mdatastandards/crosswalks. Accessed: 06/29/2010