Conventions - Signposting the Scholarly Web

Terminology

Identifying HTTP URI	An HTTP URI that provides a scholarly object with a web identity that is intended to be persistent. The intended persistence can be achieved by means of cross-portal infrastructure (e.g. DOI, handle, PURL, W3ID, ...). Typically, an Identifying HTTP URI does not provide content itself but rather redirects to another HTTP URI that does.
Repository Stable HTTP URI	An HTTP URI minted by a repository or a portal, and specifically intended to remain stable over time.
Entry Page	The page in a publisher's portal where one typically enters when accessing a scholarly publication, usually by following redirects from an Identifying HTTP URI or via a search engine result. In some portals, the Entry Page is the landing page, in others the Entry Page is an HTML version of the publication.
Publication Resource	Any web resource that is considered to be an integral part of a publication. Typical scholarly publications have several associated Publication Resources, such as a PDF version of an article, an HTML version of an article, supplementary information in various formats, datasets, etc.
Bibliographic Resource	A web resource that describes the publication in a structured manner, for example, using BibTeX or RIS formatting styles. The resource is available at a URI that supports `HTTP GET`.
Author Identifying HTTP URI	An HTTP URI that identifies the author of a publication and is intended to be persistent.
Author Description Page	A web resource that provides information about an author, for example, a resource that lists an author's scholarly publications and other metadata. This resource either could provide information that is maintained by single publisher or a repository, or it could be a service that provides information by aggregating across repositories.

Relation Types for Typed Links

Relation Types are generally registered in the IANA Link Relation Registry, which also describes their meaning and links to the specification in which they were originally defined. The Relation Types used for Signposting are repeated below, with reference to the pattern in which they are applied.

Relation Type	Signposting Pattern	Description
`author`	Author	The resource that is the target of the link is a web resource that identifies the author of the publication. In the Author pattern, the Identifying HTTP URI, the Entry Page, and the Publication Resource links to the Author of the publication using the `author` relation type. The `author` relation type may be repeated if there are multiple authors for a publication.
`collection`	Publication Boundary	The resource that is the target of the link is a collection to which the resource that provides the link belongs. In the Publication Boundary pattern, the Entry Page is modeled as a collection. Each Publication Resource link to the Entry Page using the `collection` relation type.
`describedby`	Bibliographic Metadata	The resource that is the target of the link is a description of the resource that provides the link. In the Bibliographic Metadata pattern, the Entry Page links to a Bibliographic Resource using the `describedby` relation type.
`describes`	Bibliographic Metadata	The resource that is the target of the link is described by the resource that provides the link. In the Bibliographic Metadata pattern, a Bibliographic Resource links to the Entry Page using the `describes` relation type.
`item`	Publication Boundary	The resource that is the target of the link belongs to a collection, which is the resource that provides the link. In the Publication Boundary pattern, the Entry Page is modeled as a collection. It links to each Publication Resource using the `item` relation type.
`cite-as`	Publication Boundary, Identifier	The resource that is the target of the link is the Identifying HTTP URI of the resource that provides the link. In the Publication Boundary pattern, each Publication Resource links to the Identifying HTTP URI using the `cite-as` relation type. In the Identifier pattern, the Author Description Page links to the preferred Author Identifier using the `cite-as` relation type.
`type`	Bibliographic Metadata, Publication Boundary, Resource Type	The resource that is the target of the link indicates the nature of the resource that provides the link, e.g. whether it is a landing page, a publication, a dataset, ... In the Publication Boundary pattern, the Entry Page and each Publication Resource uses a link with the `type` relation type to express its own nature. In the Bibliographic Metadata pattern, each Bibliographic Resource uses this relation type to indicate its descriptive nature. Values to be used are listed in the section URIs to express the nature of a scholarly resource. In the Resource Type pattern, the Identifying HTTP URI and the Author Identifier expresses their resource type using `type`.

Attributes for Typed Links

There is currently no official registry for attributes that can be used on Typed Links. The most common ones are listed in the Web Linking RFC. The attributes that are important for Signposting are listed below, with reference to the pattern in which they are applied.

Attribute	Signposting Pattern	Description
`formats`	Bibliographic Metadata, Publication Boundary	The value of the `formats` attribute indicates the profile to which the resource that is the target of the link conforms. Generally, a profile is a syntactic and/or semantic constraint that applies beyond what can be expressed using the MIME type of the resource. The `formats` attribute is, for example, useful when different Bibliographic Resources have the same MIME type (e.g. `application/xml`) but conform to a different schema. The value of the `formats` attribute is a URI that uniquely identifies the format (e.g. `XML Schema URI`). The `formats` attribute is defined in the HTTP Link Hints RFC that is in the making.
`type`	Bibliographic Metadata, Publication Boundary	The value of the `type` attribute conveys the MIME type of the resource that is the target of the link on which the attribute is used.

Bibliographic Metadata Formats

Currently, there are no MIME types registered to unambiguously identify bibliographic metadata formats that are commonly used in scholarly communication. And several unregistered MIME types are used to refer to the same format. For example, BibTeX is referred to by means of application/x-bibtex, application/force-download, and text/plain. RIS is referred to by means of application/x-research-info-systems, application/force-download, and text/plain.

Preferably, MIME types for bibliographic metadata formats should be registered. But CrossRef, DataCite, and mEDRA have established an interoperable practice to access bibliographic metadata using content negotiation on the basis of unregistered MIME types for three formats. Since Signposting is all about pragmatism it uses these de-facto MIME types for interoperability; they are listed in the below table. These MIME types are used in describedby links that point to Bibliographic Resources and should be expressed by a client in the Accept HTTP Request header when accessing the URI that is the target of a describedby link.

Format	MIME Type
BibTeX	`application/x-bibtex`
CiteProc JSON	`application/vnd.citationstyles.csl+json`
RIS	`application/x-research-info-systems`

Many other bibliographic formats are in use and many share text/plain, application/xml, application/json, or application/ld+json as MIME types. In order to distinguish between formats of a same MIME type, either a dedicated MIME type should be registered or a profile attribute can be used on a describedby link to clarify the format beyond its MIME type. The former allows for content negotiation for the format, the latter does not. The below table shows how the profile approach can be used for popular XML-based formats. Note that the use of the profile attribute for application/ld+json is standardized; it is not for text/plain, application/xml, application/json.

Format	`type` Attribute Value	`profile` Attribute Value
MARC XML	`application/xml`	`http://www.loc.gov/MARC21/slim`
MODS	`application/xml`	`http://www.loc.gov/mods/`
Simple Dublin Core	`application/xml`	`http://purl.org/dc/elements/1.1/`
Qualified Dublin Core	`application/xml`	`http://dublincore.org/documents/dcmi-terms/`