Moving Between Standards (Crosswalking)

Crosswalks are 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. The crosswalk may be presented as a document for humans to read, in which case the crosswalking process must be performed by humans who are referencing the document. Alternatively, a crosswalk document may be expressed in such a way that a computer can automatically perform a mapping from one metadata standard to another.

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 simultaneously change the format and fields (i.e., the content standard) 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 fields (i.e., the vocabulary) to meet the requirements of the second standard.

Due to the complexity of metadata content standards, there are few automated processes to crosswalk between content standards. Even in those cases where 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 that the standards apply to. In this case, even manual translation between standards does not result in complete information transfer.

The Crosswalking Process

The process of mapping between content standards or vocabularies is usually divided into the following steps: harmonizationIn the context of crosswalking, metadata schema of the source and the target standards are represented in the same syntax during harmonization. Related Guide, semantic mappingsIn the context of crosswalking, elements in the source schema are explicitly mapped to elements in the target schema during semantic mapping. Related Guide, rulesIn the context of crosswalking, rules are a process which define how to deal consistently with complex element mappings. Rules are created and applied during the mapping of elements from the source schema to the target schema, when one-to-one relationships between schema elements do not exist. Related Guide, and transformationIn the context of crosswalking, transformation is the process of creating a target instance of the metadata description from the source instance. Related Guide. Each of these is described in a separate guide linked below.