Crosswalk (metadata)
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A schema crosswalk is a table that shows equivalent elements (or "fields") in more than one
database schema The database schema is the structure of a database described in a formal language supported by the database management system (DBMS). The term "schema" refers to the organization of data as a blueprint of how the database is constructed (divide ...
. It maps the elements in one schema to the equivalent elements in another. Crosswalk tables are often employed within or in parallel to
enterprise systems Enterprise software, also known as enterprise application software (EAS), is computer software used to satisfy the needs of an organization rather than individual users. Such organizations include businesses, schools, interest-based user groups, ...
, especially when multiple systems are interfaced or when the system includes
legacy system In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system", yet still in use. Often referencing a system as "legacy" means that it paved ...
data. In the context of Interfaces, they function as an internal
Extract, Transform, Load In computing, extract, transform, load (ETL) is a three-phase process where data is extracted, transformed (cleaned, sanitized, scrubbed) and loaded into an output data container. The data can be collated from one or more sources and it can also ...
(ETL) mechanism. For example, this is a
metadata Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...
crosswalk from
MARC standards MARC (machine-readable cataloging) standards are a set of digital formats for the description of items catalogued by libraries, such as books, DVDs, and digital resources. Computerized library catalogs and library management software need to st ...
to
Dublin Core 220px, Logo image of DCMI, which formulates Dublin Core The Dublin Core, also known as the Dublin Core Metadata Element Set (DCMES), is a set of fifteen "core" elements (properties) for describing resources. This fifteen-element Dublin Core has ...
: Crosswalks show people where to put the data from one scheme into a different scheme. They are often used by libraries, archives, museums, and other cultural institutions to translate data to or from MARC standards, Dublin Core,
Text Encoding Initiative The Text Encoding Initiative (TEI) is a text-centric community of practice in the academic field of digital humanities, operating continuously since the 1980s. The community currently runs a mailing list, meetings and conference series, and main ...
(TEI), and other metadata schemes. For example, an archive has a MARC record in its catalog describing a manuscript. Suppose the archive makes a digital copy of that manuscript and wants to display it on the web along with the information from the catalog. In that case, it will have to translate the data from the MARC catalog record into a different format, such as
Metadata Object Description Schema The Metadata Object Description Schema (MODS) is an XML-based bibliographic description schema developed by the United States Library of Congress' Network Development and Standards Office. MODS was designed as a compromise between the complexity o ...
, that is viewable on a webpage. Because MARC has various fields than MODS, decisions must be made about where to put the data into MODS. This type of "translating" from one format to another is often called "metadata mapping" or "field mapping," and is related to "
data mapping In computing and data management, data mapping is the process of creating data element mappings between two distinct data models. Data mapping is used as a first step for a wide variety of data integration tasks, including: * Data transformatio ...
", and " semantic mapping". Crosswalks also have several technical capabilities. They help databases using different metadata schemes to share information. They help metadata harvesters create union catalogs. They enable search engines to search multiple databases simultaneously with a single query.


Challenges for crosswalks

One of the biggest challenges for crosswalks is that no two metadata schemes are 100% equivalent. One scheme may have a field that doesn't exist in another scheme or a field that is split into two different fields in another scheme; this is why you often lose data when mapping from a complex scheme to a simpler one. For example, when mapping from MARC to Simple Dublin Core, you lose the distinction between types of titles: Simple Dublin Core only has one "Title" element, so all of the different types of MARC titles get lumped together without further distinctions. This is called "many-to-one" mapping. This is also why once you've translated these titles into Simple Dublin Core, you can't translate them back into MARC. Once they're Simple Dublin Core, you've lost the MARC information about what types of titles they are, so when you map from Simple Dublin Core back to MARC, all the data in the "Title" element maps to the basic MARC 245 Title Statement field. This is why crosswalks are said to be "lateral" (one-way) mappings from one scheme to another. Separate crosswalks would be required to map from scheme A to scheme B and from scheme B to scheme A.


Difficulties in mapping

Other mapping problems arise when: * One scheme has one element that needs to be split up with different parts of it placed in multiple other elements in the second scheme ("one-to-many" mapping) * One scheme allows an element to be repeated more than once while another only allows that element to appear once with multiple terms in it * Schemes have different data formats (e.g. ''John Doe'' or ''Doe, John'') * An element in one scheme is indexed, but the equivalent element in the other scheme is not * Schemes may use different controlled vocabularies * Schemes change their standards over time Some of these problems are not fixable. As Karen Coyle says in "''Crosswalking Citation Metadata: The University of California's Experience,''"
"The more metadata experience we have, the more it becomes clear that metadata perfection is not attainable, and anyone who attempts it will be sorely disappointed. When metadata is crosswalked between two or more unrelated sources, there will be data elements that cannot be reconciled in an ideal manner. The key to a successful metadata crosswalk is intelligent flexibility. It is essential to focus on the important goals and be willing to compromise to reach a practical conclusion to projects."in "Metadata in Practice" Diane I. Hillmann and Elaine L. Westbrooks, eds., American Library Association, Chicago, 2004, p. 91.


See also

*
Meta element Meta elements are tags used in HTML and XHTML documents to provide structured metadata about a Web page. They are part of a web page's head section. Multiple Meta elements with different attributes can be used on the same page. Meta elements can ...
*
Metadata Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...
*
Database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...


References

{{Reflist


External links


"Metadata Crosswalk Depository" (SchemaTrans)
OCLC)
"Mapping Between Metadata Formats"
(UKOLN)

(Getty)

(D-Lib) Data management Knowledge representation Library cataloging and classification Metadata Technical communication