COAR Roadmap: Future Directions for Repository Interoperability stresses that still many challenges remain with improving data (based on semantic) interoperability. Besides the necessity to use the most common standardized controlled vocabularies, metadata and indicators, the interoperability issue is also in line with the objective of striving for FAIR data, because you need to ensure you deliver Linked Data models that allow the publishing and connecting structured data on the web.

Linked Data (LD) - a term coined by Tim Berners-Lee in his design note regarding the Semantic Web architecture -, refers to a set of best practices for publishing, sharing, and interlinking structured data on the Web. LD aims to connect related data formerly isolated in small or large repositories (often called “silos”) and not previously linked. 

... support the selection of appropriate encoding strategies for producing meaningful Linked Open Data (LOD)-enabled bibliographical data (directly or indirectly), thus harmonizing the encoding description (metadata properties) according to Linked Open Data (LOD)-enabling strategies. 

Albeit given progresses in metadata modeling, it is difficult to understand why different data providers - producing and managing their bibliographical data - continue to cope with difficulties in disseminating efficiently these data on the Web. To address this dilemma, the following questions may arise:

1.) Is there any uniform well-structured metadata modelling and encoding methodology (in spite of concurrent proliferation of metadata standards) able to ensure maximum interoperability among digital objects (confined in heterogeneous environments) on the frontline of Linked (Open) Data?

Different communities (e.g. Metadata2020, FAIRsharing) are working hard to find solutions to common community-specific problems linked to the creation and use of metadata and other vocabularies. 

2.) What are the significant metadata properties related to the reuse of digital data and how can these significant properties be identified and expressed, while ensuring accuracy, enhancing and preserving the meaning of data conveying specific information and knowledge of their user communities?

As a reference tool, LODE-BD provides assistance on how to make decisions on modeling (in both depth and detail) of significant metadata properties, their encoding (that enables data re-use) and implementation (with better response to local or specific needs) insuring sharing of meaningful (with clear purport) and comprehensive (both to humans and Web engines) bibliographic data.

With regard to metadata encoding, LODE-BD clarifies what kind of Vocabularies and Knowledge Organisation Systems (KOS) values (literal form representing or URI identifying a concept) should be used to produce high-quality LOD-enabled bibliographic data, easily exchangeable through repositories and sharable on the Web of Data.

To ensure and achieve high level of interoperability exploiting optimal degree of metadata LOD-readiness, LODE-BD recommend to:

The LODE-BD recommendations are applicable for structured data describing bibliographic resources such as articles, monographs, theses, conference papers, presentation materials, research reports, learning objects, etc. – in print or electronic format., and focus on nine groups of metadata: 

1. Title information; 
2. Responsible Body; 
3. Physical Characteristics; 
4. Location; 
5. Subject; 
6. Description of content; 
7. Intellectual property; 
8. Usage;  
9. Relation 

The core component of LODE-BD contains a set of recommended decision trees for common properties used in describing a bibliographic resource instance. Each decision tree is delivered with various acting points and the matching encoding suggestions.

(Decision Tree: Resource has Subject/Topic)

The full range of options presented by LODE-BD will enable data providers to make their choices according to their development stages, internal data structures, and the reality of their practices.

LODE-BD appendixes also provide lists of references related to Linked Data:

• 4.2. How to publish and consume Linked Data
• 4.3. Where to find Linked Data sets and Vocabularies
• 4.4. How to express metadata with different syntaxes: text, html. xml, rdf, and rdfa
• 4.5. Why publish bibliographic data as Linked Data?

...Then You might be interested in:

• taking a look at the COAR Case Study Controlled Vocabularies and PHAIDRA International;
• watching a Lecture 'Controlled vocabularies and PHAIDRA International' (by Imma Subirats, during the 20th International Conference on Electronic Publishing entitled 'Positioning and Power in Academic Publishing: Players, Agents and Agendas', June 7-9 2016 at Göttingen State and University Library). 

To learn more about metadata harmonisation in PHAIDRA Digital Repository of the University of Vienna, you can also check:

• The implementation of a PHAIDRA Classification Server to assist with metadata harmonization when implementing a long term preservation system of digital objects, Deliverable (2017), by Kopacsi et al.;
• COAR Resource Type Vocabulary in the Classification Server of PHAIDRA, Slides (2017), by Sandor et al.;
• IMPLEMENTATION OF A CLASSIFICATION SERVER TO SUPPORT METADATA ORGANIZATION FOR LONG TERM PRESERVA-TION SYSTEMS, by Kopacsi et al.;, in VÖB 70 (2017) Nr. 2: Metadata;
• Development of a Classification Server for organizing data in a long term Preservation System, Report (2016), by Kopacsi et al.;
• Requirements of the PHAIDRA Classification Server, by Kopacsi, in GitHub.

​RELATED: 

• To find available LOD datasets, check, e.g., the Data Hub (check under certain groups, such as 'Bibliographic Data', 'Library Linked Data' group); LOD cloud

• To find metadata schemas/vocabularies, or find the properties already being defined by any RDF vocabulary or OWL ontology, check, e.g., Linked Open Vocabularies (LOV) [Find a vocabulary or check its relationship with other vocabularies. Search a property name you are looking for, e.g., 'audiance' and find out which namespaces have defined it]

• For Name Authorities, check, e.g., Virtual International Authority File (VIAF)
• For LOD Subject Vocabularies, check, e.g., Basel Register of Thesauri, Ontologies & Classifications (BARTOC) and its vocabulary browser https://bartoc-skosmos.unibas.ch - Directory contains nearly 3,000 vocabularies, browser includes more than 3.1 Mio SKOS concepts and more than 11 Mio terms; AGROVOC (multilingual) Linked Open Data; Library of Congress Subject Headings (LCSH); EUROVOC multilingual thesaurus
• Publishing Library Metadata as Linked Data (video, by Lars G. Svensson)
• Examples of bibliographic data that are available as LOD: the International System for Agricultural Science and Technology (AGRIS) [for e.g., 'search for rice' and follow one record to check its RDF record); e.g.: http://agris.fao.org/openagris/search.do?recordID=PL2009000495]; WorldCat [go to the end of any record page, click 'Linked Data' box; e.g.: http://www.worldcat.org/title/oliver-twist/oclc/959213]
• The RDA IGAD Agrisemantics Collection Of Use CAses (Report, 2018)
• Data standards for Agriculture: INRA adoption of RDA Outputs (Report, 2019)

• Vocabularies for Semantic Interoperability in Agriculture: discover Agrisemantics map with up to 400 standards for data exchange

• Metadata Basics. Controlled Vocabularies (University of Texas Libraries)
• Publications about Metadata Modeling and Knowledge Organisation Systems, by Marcia Lei Zeng
• FAIRsharing: working with and for the community to describe and link data standards, repositories and policies, by Sansone et al., in BioRxiv, Preprint (2018)
• Harmonized terms, concepts and metadata for microbiological risk assessment models: The basis for knowledge integration and exchange, by Haberbeck et al., in Microbial Risk Analysis, Volume 10, December 2018
• Scientific Publications about Discovering, Indexing and Interlinking Information Resources (SemaGrow)
• Using Controlled Vocabulary: an introduction to the concept and use of controlled vocabulary to increase database and catalog searching skills
• Use COAR Controlled Vocabularies to enhance the Interoperability across repositories and with other related systems
• Metadata 2020: a community collaboration to advance metadata for scholarly communications
• Metadata 2020: A holistic approach to metadata improvements for scholarly communications
• The OCLC Terminologies Service: Work with a controlled vocabulary

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