For a complete specification of the FDP metadata items, see spec.md.

• Introduction
  • Purpose
  • Product scope
• Overall Description
  • Usage Scenarios
    • Data discovery
    • Data access
    • Data publication
    • Data metrics gathering
  • Goals
  • Product perspective
• Architecture
• Metadata model specification
• External interfaces
  • Application Programming Interface (API)
    • Metadata Provider API
    • Current implementation
• Characterisation

FAIR Data Point (FDP) is a metadata repository that provides access to metadata in a manner that follows the FAIR (Findable, Accessible, Interoperable, and Reusable) Principles for data/metadata publishing. FDP uses a REST API for creating, storing and serving FAIR metadata. FDP is a software that, from one side, allows digital objects owners/publishers to expose the metadata of their digital objects in a FAIR manner and, for another side, allows digital objects' consumers to discover information (metadata) about offered digital objects. Commonly, the FAIR Data Point is used to expose metadata of datasets but metadata of other types of digital objects can also be exposed such as ontologies, repositories, analysis algorithms, websites, etc.

A basic assumption for the FDP is its distributed nature. We believe that big warehouses spanning multiple domains are not feasible and/or desirable due to issues concerning scalability, separation of concerns, data size, costs, etc. A completely decoupled and distributed infrastructure also does not seem realistic. The scenario we envision has a mixed nature, with a number of reference repositories, containing a relevant selection of core digital objects, e.g., EBI's repositories, Zenodo, BioPortal, etc., integrated with smaller distributed repositories, e.g., different biobanks, digital objects' repositories created within the scope of research projects, etc. Many different repositories and their digital objects should interoperate in order to allow increasingly complex questions to be answered. Interoperability, however, takes place in different levels, such as syntactical and semantical. A collection of FDPs aim to address this interoperability issues by enabling digital objects' producers/publishers to share the metadata of their objects in FAIR manner and, therefore, fostering findability, accessibility, interoperability and reusability.

The main goal of the FDP is to establish a common method for metadata provisioning and accessing and, as a consequence, (client) applications have a predictable way of accessing and interacting with metadata content. To fulfill this goal, we created two types of artefacts. A set of specifications to help developers extend the funciontalities of their applications so that they behave also as FAIR Data Points and a reference application for those who would like to have the FDP functionality in a stand-alone web application.

The purpose of this document is to specify the FAIR Data Point (FDP) software. This document includes requirements, architecture and design of the FDP software. This specification is primarily intended to be a reference for developer willing to add the FDP functionality into their existing applications.

From the different interoperability projects we have been and are involved, the following usage scenarios have been identified. We used these usage scenarios to derive the requirements for the metadata storage and accessibility infrastructure and guide the design and development of the solution.

A researcher needs to find datasets containing data about his/her insterested subject such proteins that are activated in specific tissues, polution level in a given region or infrared observation of a particular galaxy, combine these data and analyse them. In another situation, the researcher needs to know which biobanks carry a given type of biosample (e.g., blood samples) from patients possessing a specific phenotype (e.g., Alzheimer's disease) taken from a patient registry whose onset age was lower than 45 year-old. These data users need to use a straightforward search application that allows them to find the required information.

Once a data user/consumer finds where the needed datasets, including the information about their licenses and access protocols, the user wants to access the data, retrieving it or send an algorithm to analyse the data. In many situations the data user will integrate many different datasets. To carry out this integrations, the user needs to know in which formats, structure the data can be accessed and which access methods are available. This information comes in the former of metadata. In order to facilitate the usage of metadata, the method with which the metadata will be accessed should be common in all different metadata sources and a common representation technology should be used for the metadata.

A research group is running a project in which data is being created. As the data will be used during the project for analysis and may also be useful for other users, the group would like to publish them in a way that allows potential users of the data to retrieve information about the datasets (metadata), data search engines to index the datasets' metadata, and users to retrieve the data. Some of the produced datasets have an open license but others have more restrictive licenses. All these metadata should be available in terms of metadata so that potential data users would have enough information to asses whether the data described in the metadata fits their needs.

From the usage scenarios, we have identified a need for a metadata provisioning infrastructure that we call FAIR Data Point (FDP). The FDP has the following goals:

• Allow owners/creators/publishers to expose the metadata of their digital objects in a way that follows the FAIR Data Principles.
• Allow consumers/users to discover information about digital objects they are interested on.
• Allow interaction for both humans (GUI) and software agents (API).

Based on these goals, Figure 1 depicts the general architecture of an FDP. In this architecture, the FDP exposes its functionality to the users through an application programming interface (API). In our reference implementation, besides the FDP itself we developed a FDP web client, which connects to the FDP API and allows human users to interact with the application through a web-based interface.

Figure 1 also depicts the FDP's internal components, namely the Metadata Provider, Access Control, Metadata Schemas and the RDF Metadata Store.

• Metadata Provider - responsible for the provisioning of the metadata content available in the FDP;
• Access Control - reposible for controlling the access to the metadata content. In general, metadata is openly accessible for reading but is expected that only a selected number of people have access to add, delete or edit the metadata content. Moreover, in some situations, metadata or part of the metadata may also have access restrictions for reading. The Access Control component makes sure that these restrictions are enforced;
• Metadata Schemas - the FDP exposes metadata about different types of digital objects, e.g., repositories, content catalogs and datasets, among others. These metadata should comply with schemas defined by their related communities. The FDP reference implementation is shipped with four basics metadata schemas for the the FDP itself as a (metadata) repository, for catalogs, for datasets and for datasets' distributions. These schemas allows the FDP to check and validate metadata content that is added. Addition of metadata schemas for other types of digital objects or extension to the base schemas are supported by the FDP reference implementation. The metadata schemas are expressed in SHACL;
• RDF Metadata Source - The FDP handles metadata in RDF. Therefore, these metadata should be stored in a RDF Metadata Source. The FDP reference implementation support native in-memory or in-disk storage as well as the connection with existing triple stores such as GraphDB, Allegro Graph, Blazegraph, etc. If one is extending an existing application based on this FDP specification, the RDF metadata can be provided using different implementation strategies. For instance, metadata stored in other representation formats can be dynamically converted to RDF through a conversion compoenent that serves as the RDF Metadata Source.

Fig. 1 - FDP General architecture based on the application's goals

The FDP has initially two usage purposes: (i) to be used as a stand-alone web application, where data owners give access to their datasets in a FAIR manner and, (ii) to be integrated in larger data interoperability systems, such as the FAIRport, providing the dataset accessibility functionality for such systems. Figure 2 depicts an FDP as a stand-alone application deployed in a web server, exposing to the Web its API and GUI. In the figure we have a FDP Web Client from the FDP's reference implementation and other 3rd party client applications interacting with the FDP's API. Figure 3 depicts an application with its own specific functionality, storage facility and API being extended to also behave as a FDP to allow it to expose metadata of itself and its content in a FAIR way.

Fig. 2 - FDP as a stand-alone Web application

Fig. 3 - FDP as an application extension

In this section we use elements from the Archimate notation. The ArchiMate modelling language is an open and independent Enterprise Architecture standard that supports the description, analysis and visualisation of architecture within and across business domains. ArchiMate is one of the open standards hosted by The Open Group and is fully aligned with TOGAF.

Figure 4 depicts a view of the current architecture of the FDP using Archimate's Application layer notation. From top down, we have the Archimate's Application Interface representing the FDP's API. This API is currently composed of two parts, the Metadata Provider API and the FAIR Data Accessor API. The Metadata Provider API is the public interface of the Metadata Provider Service. Similarly, the FAIR Data Accessor API is the public interface of the FAIR Data Accessor Service.

The Metadata Provider Service realises the Metadata Retrieval function while the FAIR Data Accessor Service realises the Data Access function. As sub-functions of the Metadata Retrieval function we have:

• FDP Metadata Retrieval: retrieves the FDP Metadata (represented by Archimate's Data Object). The FDP Metadata is composed by a number of Catalog Metadata. FDP Metadata Retrieval function lead to the Catalog Metadata Retrieval function by appending the URIs of the Catalog Metadata at the end of the FDP Metadata content.
• Catalog Metadata Retrieval: retrieves the Catalog Metadata. The Catalog Metadata is composed by a number of Dataset Metadata. The Catalog Metadata Retrieval function lead to the Dataset Metadata Retrieval function by containing the URIs of the Dataset Metadata in the Catalog Metadata content.
• Dataset Metadata Retrieval: retrieves the Dataset Metadata. The Dataset Metadata can have a number of Distribution Metadata. The Dataset Metadata Retrieval function lead to the Distribution Metadata Retrieval function by containing the URIs of the Distribution Metadata in the Dataset Metadata content. Also, The Dataset Metadata can have a Data Record Metadata. The Dataset Metadata Retrieval function can lead to the Data Record Metadata Retrieval function by appending the URI of the Data Record Metadata in the Dataset Metadata content.
• Distribution Metadata Retrieval: retrieves the Distribution Metadata. The Distribution Metadata describes information about the concrete representation of the dataset such as file format, access or download URL, size, etc.
• Data Record Metadata: retrieves the Data Record Metadata. The Data Record Metadata describes the structure and content of the dataset such as involved types, domain and range of the values, relations among the types, etc.

The FAIR Data Accessor Service realises the Data Access function. In its turn, the Data Access is subdivided in Linked Data Platform Access (LDP Access) and Linked Data Fragments Access (LDF Access). These two options of FAIR Data Access give access to the actual data in a FAIR Format.

The details of what each of these metadata object represent are given in the Metadata section below in this document. Also, the details of the FAIR Data Point API are given below in this document at the Application Programming Interface (API) section.

Fig. 4 - FDPs’ Archimate Application layer architecture

See spec.md for the metadata model specification.

The FDP's API follows the REST architectural style and, more specifically, the Hypermedia as the Engine of Application State (HATEOAS) pattern. In summary, a HATEOAS API provides information on how to navigate through the API even if the client does not have previous knowledge of the interface.

Figure below depicts the HATEOAS RESTful API of FDP. In the figure, the upper-left box represents the FDP service and responds to requests to the root URL, hereby represented as "/".

When the FAIR Data Point Service root URL receives an HTTP GET request (e.g., http://mydomain.com/fdp/), the Metadata Service returns the FDPMetadata resource. This resource contains information about the FDP itself such as the owner (organisation or individual), FDP version, API version, etc. The content of the FDPMetadata resource is based on the Repository concept defined in the Open Initiative Archive Protocol for Metadata Harvesting (OAI-PMH). Following the HATEOAS guidelines, the FDPMetadata resource also provides a link to the CatalogMetadata resource.

The CatalogMetadata resource provides a list of links of DatasetMetadata resources for each of the datasets offered by the FDP. This resource is equivalent to W3C's DCAT Catalog concept. An example URL: http://mydomain.com/fdp/comparativeGenomics.

The DatasetMetadata resource provides information about the each of the offered datasets. Information includes datasets owner, license, distribution, etc. This resource is equivalent to W3C's DCAT Dataset. An example URL: http://mydomain.com/fdp/comparativeGenomics/goNlSvR5 .

The DistributionMetadata resource provides information about the distribution of a dataset. Information includes license, downloadURL or accessURL of a dataset distribution. This resource is equivalent to W3C's DCAT Distribution. An example URL: http://mydomain.com/fdp/comparativeGenomics/goNlSvR5/turtleFile .

The main aim of this specification is to guide developers in implementing their own FAIR Data Point or in extending their existing applications to also behave as a FAIR Data Point and, therefore, expose their metadata in a FAIR way.

In order to classify an application as a FAIR Data Point, it has to present the the following characteristics:

• Its root API URL must provide the Repository metadata (see Metadata specification);
• The metadata content must be present in, at least, RDF Turtle and JSON-LD. Other formats such as XML and JSON are allowed through content negotiation but the default media type must be RDF Turtle;
• Each metadata record should have a reference to its own profile which, on its turn, points to the metadata schema expressed in SHACL;
• The metadata schema expressed in SHACL must have as its target class, a subclass of dcat:Resource;
• The information about how to navigate the metadata content structure must be provided in each metadata record using the Linked Data Platform (LDP) containment structure (ldp:hasMemberRelation);

The goal of defining FDP specifications such that developers could implement these instructions in their applications is to guarantee a minimal level of predictability and interoperability in this growing ecosystem. But for this goal to be achieved, we have to guarantee that applications that claim to implement the FDP behaviours really follow the specifications. Therefore, it is necessary to have a way of verifying the compliance of a given implementation with the specs. Since the FDP specifications focus on its external behaviours and not on internal implementation, it is possible to automate the verification of whether an application in fact exposes the claimed FDP behaviours. This compliance validation is done based on the characterisation items mentioned in the section above.