Use Case Component Vocabularies
From Library Linked Data
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Background and Current Practice
Creators of metadata use a variety of methods to encode or reference entities associated with the resource described, e.g. names, title, subjects, geographic names, etc. XML schemas sometimes permit the direct inclusion of the terms along with authority attributes, or sometimes allow an XLink reference to an external reference. But these methods can be cumbersome and confusing, and in some cases they are not well-specified.
1. The goal is to allow metadata to link to established vocabularies. 2. Linked data technology may be used to achieve this, by assigning URIs to vocabulary terms.
Catalogers, technologists, machines (in order to provide information to end users).
Use Case Scenario
- A cataloger creating a bibliographic description inserts links to controlled vocabulary terms as applicable, such as Library of Congress Subject Headings (LCSH) or language codes. For example, for the role ‘architect’, instead of entering the term itself, the URI (http://id.loc.gov/vocabulary/relators/arc) for the term within the controlled vocabulary at id.loc.gov is entered. When a user accesses the description, the local system follows the link and fills in the term for the local version of the description that it presents to the user. The local system might cache the vocabulary terms, that is, keep a table of URIs and corresponding terms, and refresh it periodically. As another example: for the subject “garlic”, the LCSH URI http://id.loc.gov/authorities/sh85053172#concept is entered.
- Authority records are exposed in RDF. Bibliographic descriptions, also in RDF, link to the RDF authority descriptions for names, titles, subjects.
Application of linked data for the given use case
Linked data is employed as follows. URIs are assigned to vocabulary terms in the controlled vocabularies, and metadata descriptions at external systems use the URIs to reference those terms.
Here you can list and clarify the use of vocabularies (element sets and value vocabularies) which can be helpful and applied within this context.
- MADS in RDF
Problems and Limitations
- The underlying assumption is that when a user accesses a metadata description with linked data to vocabulary terms, then either:
- the system will follow all the links for every access; or
- the system will perform some level of caching.
Obviously the first will cause too heavy a burden on the supplying system and so some level of caching will be necessary. But what level? How can the system know if a particular subject heading has been superseded? How often will it need to refresh?
- Multi-facet headings with separately identifiable components require more granular markup if the linked data is to be fully exploited.
Related Use Cases and Unanticipated Uses
- Multilingual access to subject headings via linked data.
Library Linked Data Dimensions / Topics
- Information lifecycle --> present / publish --> create or update entities
- Information assets --> Thesauri and controlled vocabularies
- Vocabularies --> Best practice for the description of personal names and name variants
- linked data management, hosting, and preservation --> Caching strategies
- Authorities & Vocabularies (http://id.loc.gov)