Federation Description Vocabulary for HeFQUIN

An entity that is part of the federation and provides access to data via a specific interface. Every federation member must have an fd:serviceURI property and an fd:interface property. This class is a superclass of any kind of federation member and should not be used directly within federation descriptions. Concrete types of federation members, to be used in federation descriptions, are captured by the subclasses of this class.

• service URI ^dp
• interface ^op
• parallel request limit ^dp

• RDF-based Federation Member ^c
• Wrapped Federation Member ^c

A federation member whose interface exposes RDF data. Every such federation member must have the two properties that are expected for any kind of federation member (i.e., fd:serviceURI and fd:interface), where the fd:interface may be either an fd:FixedEndpointInterface with the fd:supportedProtocol being fd:SPARQLProtocol or an fd:FragmentInterface. Additionally, an RDF-based federation member may have an fd:vocabularyMappingsFile property.

A federation member that provides access to non-RDF data, for which it is associated with a wrapper that defines and RDF view of the data of that federation member. In addition to the properties that are expected for any kind of federation member (i.e., fd:serviceURI and fd:interface), such a wrapped federation member must have an fd:wrapper property.

An interface is a means to issue data retrieval requests to a federation member. This class is a superclass of any kind of interface and should not be used directly within federation descriptions. Concrete types of interfaces, to be used in federation descriptions, are captured by the subclasses of this class.

• Fixed Endpoint Interface ^c
• Template-based Interface ^c
• Fragment Interface ^c

An interface that can be accessed via a single, fixed endpoint address. Every such interface must have an fd:endpointAddress property and an fd:supportedProtocol property. The value for the fd:supportedProtocol property is expected to be one of the following: fd:SPARQLProtocol, fd:BoltProtocol, fd:GraphQLProtocol, or fd:GenericWebAPIProtocol.

An interface that can be accessed via request URIs that can be created based on a URI template. Every such interface must have an fd:uriTemplate property and an fd:supportedProtocol property. For the time being, the value for the fd:supportedProtocol property is expected to be fd:GenericWebAPIProtocol.

An interface that can be accessed via URIs that denote fragments (i.e., specific subsets) of the dataset of the corresponding federation member, where the way in which these URIs are formed is communicated in responses to requests to such an interface. Every such interface must have an fd:exampleFragmentAddress property and an fd:supportedProtocol property. The value for the fd:supportedProtocol property is expected to be either fd:TPFProtocol or fd:brTPFProtocol.

A wrapper provides a mapping for data of federation members that do not support RDF and SPARQL natively. For the time being, every such wrapper must have either an fd:rmlTriplesMaps property or an fd:mappingConfiguration property. In particular, for wrappers associated with a federation member whose interface has fd:GenericWebAPIProtocol as the fd:supportedProtocol, the wrapper must have an fd:rmlTriplesMaps property; and for wrappers associated with a federation member whose interface has fd:BoltProtocol or fd:GraphQLProtocol as the fd:supportedProtocol, the wrapper must have an fd:mappingConfiguration property.

• RML triples maps ^op
• mapping configuration ^op

Instances of this class represent the different protocols to be used when interacting with the interface of a federation member.

• SPARQL protocol ⁿⁱ
• Bolt protocol ⁿⁱ
• GraphQL protocol ⁿⁱ
• TPF protocol ⁿⁱ
• brTPF protocol ⁿⁱ
• Generic Web API protocol ⁿⁱ

A security scheme that uses a token to authenticate requests, similar to wotsec:BearerSecurityScheme but with the option to specify the name of the scheme to be mentioned in the request header (where wotsec:BearerSecurityScheme uses the fixed string 'Bearer'). To specify the name use the wotsec;name property. Otherwise, this class can be used exactly like wotsec:BearerSecurityScheme. Especially, every instance of this class must have an fd:envarForToken property and the value of the wotsec:in property, if given, must be the string 'header'.

The interface for accessing the federation member.

The data retrieval protocol supported by the interface.

The template for creating URIs that can be used for issuing requests to the interface. The template is captured as a hydra:IriTemplate, which must have a hydra:template property and, if the template contains variable parts, there must also be a hydra:mapping property for each of these variable parts.

The type of values to be used for a variable part of a URI template. This type is expected to be specified as a datatype URI (e.g., xsd:string, xsd:float). This property is optional; i.e., not every IriTemplateMapping needs to have it. If a IriTemplateMapping has this property, the datatype specified via this property is enforced when creating request URIs from the corresponding IriTemplate; i.e., the IriTemplate will be instantiated only for parameter values that have the specified datatype.

The wrapper of a wrapped federation member.

List of RML triples maps that define the mapping for a wrapper. The elements of such a list are expected to be of type rml:TriplesMap. ATTENTION: for the time being, these triples maps must all be normalized as per the definition in Section 5 of the paper titled 'An Algebraic Foundation for Knowledge Graph Construction'.

Mapping configuration for translating non-RDF data models to RDF (e.g., GraphQL, PG).

The URI via which the federation member is identified in a SERVICE clause.

The network address (URI) of the endpoint of the federation member.

An example URI of a fragment for the fragment interface.

Path to a file with RDF mappings to align different vocabularies.

Specifies a limit on the number of requests that HeFQUIN sends in parallel to the federation member. If the limit is reached and further requests are to be sent, these requests are queued until the number of currently active requests drops below the limit.

The name of the environment variable from which the username is obtained. This property is intended to be used with authentication schemes that require a username, such as wotsec:BasicSecurityScheme. At runtime, the implementation is expected to resolve the environment variable and use its value when authenticating requests.

The name of the environment variable from which the password is obtained. This property is intended to be used with authentication schemes that require a password, such as wotsec:BasicSecurityScheme. At runtime, the implementation is expected to resolve the environment variable and use its value when authenticating requests.

The name of the environment variable from which an authentication token is obtained. This property is intended to be used with token-based authentication schemes, such as wotsec:BearerSecurityScheme. At runtime, the implementation is expected to resolve the environment variable and use its value when authenticating requests.