1

Mapping and Mapping and Crosswalking Crosswalking

““Absolute Crosswalking”Absolute Crosswalking”

““Relative Crosswalking”Relative Crosswalking”

““Switching-across”Switching-across”

2

A LOM record (partial)

• hierarchical structure (not flat)

• many more elements than DC

• several elements correspond to one DC element

Think of mapping between a DC record and a LOM record

3

Common Common Crosswalking ApproachesCrosswalking Approaches

Contributor

Coverage

----------Location.CurrentRepository

Format----------Technique

Dublin CoreDublin CoreVAR Core (3.0)

Relative crosswalking

Absolutecrosswalking

Contributor

Coverage

----------Location.CurrentRepository

Format----------Technique

Dublin CoreDublin CoreVAR Core (3.0)

Relative crosswalking

Absolutecrosswalking

target

source

4

Pros and Cons Pros and Cons -- Absolute Crosswalking-- Absolute Crosswalking

• ensures the equivalency (or closely-ensures the equivalency (or closely-equivalent matches) of elementsequivalent matches) of elements

• does not work well for data conversion does not work well for data conversion • data values in non-mappable space will data values in non-mappable space will

be left out, especially when a source be left out, especially when a source schema has a richer structure than that schema has a richer structure than that of the target schema. of the target schema. – E.g., from LOM records to DC recordsE.g., from LOM records to DC records

vra:title = dc:titlevra:technique = xxx

vra:title = dc:titlevra:technique = xxx

5

Pros and Cons Pros and Cons -- Relative Crosswalking-- Relative Crosswalking

• When data conversion is conducted, at least the When data conversion is conducted, at least the values in the fields of a source database will find a values in the fields of a source database will find a place to reside in the target database. place to reside in the target database.

• Appears to work better when mapping from Appears to work better when mapping from complex to simpler schema, e.g., from MARC to complex to simpler schema, e.g., from MARC to DC, but not vice versa. DC, but not vice versa. http://www.loc.gov/marc/marc2dc.html

• The problem is that mapped elements are not The problem is that mapped elements are not really equivalent.really equivalent.

vra:title = dc:titlevra:technique = dc:format

vra:title = dc:titlevra:technique = dc:format

6

Problems exist in direct Problems exist in direct mapping when:mapping when:

• converting from a converting from a less inclusiveless inclusive format to a format to a more inclusivemore inclusive format, format,

• converting from an converting from an uncontrolleduncontrolled vocabulary vocabulary content to a content to a controlledcontrolled vocabulary content, vocabulary content,

• converting to fields where there are converting to fields where there are indirect impacts on the indirect impacts on the correspondingcorresponding fields and values, (e.g., 043 and 6xx #z),fields and values, (e.g., 043 and 6xx #z),

• data contents using data contents using differentdifferent controlled controlled vocabularies, vocabularies,

• data being converted into data being converted into non-searchablenon-searchable fields. fields.

7missed?! missed?! missing keywords

OPTIONS mapped to SUBJECT, missing all KEYWORDS

Incorrect element mapping

after …

before …

8

AUTHOR mapped to DESCRIPTION

3357 records !

no CREATOR

before …

after …

9

If re-generate records based on the embedded metadata, all can be corrected.

Incorrect values

after …

before …

10CLASSIFICATION mapped to SUBJECT and missed all the KEYWORDs.

Inappropriate mapping

missed?missed?

before …

after …

11

Missed Data ValuesMissed Data Values

• When a group of elements map to a When a group of elements map to a single one, there could be missed data single one, there could be missed data values.values.

dc:rights

12

• WHY do some data sets have 100% inaccessible IDs in a repository after a few years?

• The IDENTIFIER only provided the information of the record, such as a local access number ID. • When data were migrated or moved around in these collections’ servers, these IDs became obsolete.

Missed Data Values Missed Data Values which may cause in-accessible which may cause in-accessible

IDsIDs

13

• When crosswalking, there should be multiple elements mapped to dc:identifier element

3 identifiers

From a LOM record:

14

Switching-across Switching-across when multiple schemas are when multiple schemas are

involved. involved. Schema ASchema A

Schema BSchema B

Schema CSchema C

Schema DSchema D

SwitchSwitch

15

Mapping ProcessMapping Process

• One of the schemas is used as the One of the schemas is used as the switching mechanism among multiple switching mechanism among multiple schemas. schemas.

• Instead of mapping between every pair in Instead of mapping between every pair in the group, each of the individual metadata the group, each of the individual metadata schemas is mapped to the switching schemas is mapped to the switching schema only.schema only.

• Example: Example: http://www.getty.edu/research/conducting_research/standards/intrometadata/metadata_element_sets.html

16

Common properties in Common properties in crosswalkscrosswalks

definitiondefinition of each metadata element of each metadata element

mandatorymandatory, optional, or mandatory based on , optional, or mandatory based on certain conditionscertain conditions

may occur may occur multiplemultiple times times

constraints due to the structureconstraints due to the structure e.g., hierarchical parent-child relationshipse.g., hierarchical parent-child relationships

constraints imposed on the constraints imposed on the valuevalue e.g., free text, numeric range, date, or a controlled e.g., free text, numeric range, date, or a controlled vocabulary vocabulary

locally definedlocally defined metadata element (s) metadata element (s)

- Based on St. Pierre and Jr. William. 1998. Issues in Crosswalking Content Metadata Standards. Bethesda,

MD: NISO Press.