The Current Situation

Issues with traditional library data

Library data is not integrated with Web resources

Library data today resides in databases which, while they may have Web-facing search interfaces, are not more deeply integrated with other data sources on the Web. There is a considerable amount of bibliographic data and other kinds of resources on the Web that share data points such as dates, geographic information, persons, and organizations. In a future Linked Data environment, all these dots could be connected.

Library standards are designed only for the library community

Many library standards, such as the MAchine-Readable Cataloging format (MARC) or the information retrieval protocol Z39.50, have been (or continue to be) developed in a library-specific context. Standardization in the library world is often undertaken by bodies focused exclusively on the library domain, such as the International Federation of Library Associations and Institutions (IFLA) or the Joint Steering Committee for Development of RDA (JSC). By broadening their scope or liaising with Linked Data standardization initiatives, such bodies can expand the relevance and applicability of their standards to data created and used by other communities.

Library data is expressed primarily in natural-language text

Most information in library data is encoded as display-oriented, natural-language text. Some of the fields in MARC records use coded values, such as fixed-length strings representing languages, but there is no clear incentive to include these in all records, since most coded data fields are not used in library system functions. Some of the identifiers carried in MARC records, such as ISBNs for books, could in principle be used for linking, but only after being extracted from the text fields in which they are embedded (i.e., "normalized").

Some data fields, such as authority-controlled names and subjects, have associated records in separate files, and these records have identifiers that could be used to represent those entities in library metadata. However, the data formats in current use do not always support inclusion of these identifiers in records, so many of today's library systems do not properly support their use. These identifiers also tend to be managed locally rather than globally, and hence are not expressed as URIs which would enable linking to them on the Web. The absence or insufficient support of links by library systems raises important issues. Changes to authority displays require that all related records be retrieved in order to change their text strings -- a disruptive and expensive process that often prevents libraries from implementing changes in a timely manner.

The library community and Semantic Web community have different terminology for similar metadata concepts

Work on library Linked Data can be hampered by the disparity in concepts and terminology between libraries and the Semantic Web community. Few librarians speak of metadata "statements," while the Semantic Web community lacks notions clearly equivalent to "headings" or "authority control." Each community has its own vocabulary, and these reflect differences in their points of view. Mutual understanding must be fostered, as both groups bring important expertise to the construction of a web of data.

Library technology changes depend on vendor systems development

Much of the technical expertise in the library community is concentrated in the small number of vendors who provide the systems and software that run library management functions as well as the user discovery service -- systems which integrate bibliographic data with library management functions such as acquisitions, user data, and circulation. Thus libraries rely on these vendors and their technology development plans, rather than on their own initiative, when they want to adopt Linked Data at a production scale.

Library Linked Data available today

The success of library Linked Data will rely on the ability of practitioners to identify, re-use, or link to other available sources of Linked Data. However, it has hitherto been difficult to get an overview of libraries datasets and vocabularies available as Linked Data. The Incubator Group undertook an inventory of available sources of library-related Linked Data (see Appendix A @@@CITE@@@ ), leading to the following observations.

Fewer bibliographic datasets have been published as Linked Data than value vocabularies and element sets

Many metadata element sets and value vocabularies have been published as Linked Data over the past few years, including flagship vocabularies such as the Library of Congress Subject Headings and Dewey Decimal Classification. Key element sets, such as Dublin Core, and reference frameworks such as Functional Requirements for Bibliographic Records (FRBR) have been published as Linked Data or in a Linked Data-compatible form.

Relatively fewer bibliographic datasets have been made available as Linked Data, and relatively less metadata for journal articles, citations, or circulation data -- information which could be put to effective use in environments where data is integrated seamlessly across contexts. Pioneering initiatives such as the release of the British National Bibliography reveal the effort required to address challenges such as licensing, data modeling, the handling of legacy data, and collaboration with multiple user communities. However, they also demonstrate the considerable benefits of releasing bibliographic databases as Linked Data. As the community's experience increases, the number of datasets released as Linked Data is growing rapidly.

The quality of and support for available data varies greatly

The level of maturity or stability of available resources varies greatly. Many existing resources are the result of ongoing project work or the result of individual initiatives, and describe themselves as prototypes rather than mature offerings. Indeed, the abundance of such efforts is a sign of activity around and interest in library Linked Data, exemplifying the processes of rapid prototyping and "agile" development that Linked Data supports. At the same time, the need for such creative, dynamically evolving efforts is counterbalanced by a need for library Linked Data resources that are stable and available for the long term.

It is encouraging that established institutions are increasingly committing resources to Linked Data projects, from the national libraries of Sweden, Hungary, Germany, France, the Library of Congress, and the British Library, to the Food and Agriculture Organization of the United Nations and OCLC Online Computer Library Center, Inc. Such institutions provide a stable foundation on which library Linked Data can grow over time.

Linking across datasets has begun but requires further effort and coordination

Establishing connections across datasets realizes a major advantage of Linked Data technology and will be key to its success. Our inventory of available data (see Appendix A @@@CITE@@@) shows that many semantic links have been created between published value vocabularies -- a great achievement for the nascent library Linked Data community as a whole. More can -- and should -- be done to resolve the issue of redundancy among the various authority resources maintained by libraries. More links are also needed among datasets and among the metadata element sets used to structure Linked Data descriptions. Key bottlenecks are the comparatively low level of long-term support for vocabularies, the limited communication among vocabulary developers, and the lack of mature tools to lower the cost for data providers to produce the large amount of semantic links required. Efforts have begun to facilitate knowledge sharing among participants in this area as well as the production and sharing of relevant links (see the section on linking in Appendix B @@@CITE@@@).

Rights issues

Rights ownership is complex

Some library data has restricted usage based on local policies, contracts, and conditions. Data can therefore have unclear and untested rights issues that hinder their release as Open Data. Rights issues vary significantly from country to country, making it difficult to collaborate on Open Data publishing.

Ownership of legacy catalog records has been complicated by data sharing among libraries over the past fifty years. Records are frequently copied and the copies are modified or enhanced for use by local catalogers. These records may be subsequently re-aggregated into the catalogs of regional, national, and international consortia. Assigning legally sound intellectual property rights between relevant agents and agencies is difficult, and the lack of certainty hinders data sharing in a community which is necessarily extremely cautious on legal matters such as censorship and data privacy and protection.

Data rights may be considered business assets

Where library data has never been shared with another party, rights may be exclusively held by agencies who put a value on their past, present, and future investment in creating, maintaining, and collecting metadata. Larger agencies are likely to treat records as assets in their business plans and may be reluctant to publish them as Linked Open Data, or may be willing to release them only in a stripped- or dumbed-down form with loss of semantic detail, as when "preferred" or "parallel" titles are exposed as a generic title, losing the detail required for use in a formal citation.