Network Working Group E. Wilde
Internet-Draft UC Berkeley
Intended status: Informational April 22, 2015
Expires: October 24, 2015
Link Relation Types for Web Services
draft-wilde-service-link-rel-00
Abstract
Many resources provided on the Web are part of a sets of resources
that are provided in a context that is defined and managed by one
particular service provider. Often, these sets of resources are
referred to as "Web Services" or "Web APIs". This specification
defines two link relations that allow to represent relationships from
those resources to ones that provide documentation or descriptions of
the Web services. The difference between these concepts is that
documentation is primarily intended for human consumers, whereas
descriptions are primarily intended for automated consumers.
Note to Readers
Please discuss this draft on the apps-discuss mailing list [1].
Online access to all versions and files is available on github [2].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 24, 2015.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Web Services . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Documenting Web Services . . . . . . . . . . . . . . . . 4
3.2. Describing Web Services . . . . . . . . . . . . . . . . . 4
4. Link Relations for Web Services . . . . . . . . . . . . . . . 4
4.1. The service-doc Link Relation Type . . . . . . . . . . . 5
4.2. The service-desc Link Relation Type . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. Link Relation Type: service-doc . . . . . . . . . . . . . 5
5.2. Link Relation Type: service-desc . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
One of the defining aspects of the Web is that it is possible to
interact with Web resources without any prior knowledge of the
specifics of the resource. By using URIs, HTTP, and media types, the
Web's uniform interface allows interactions with resources without
the more complex binding procedures of other approaches.
However, many resources on the Web are provided as part of a set of
resources that are referred to as a "Web Service" or a "Web API". In
many cases, these services or APIs are defined and managed as a
whole, and it may be desirable for clients to be able to discover
this service definition information.
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Service definition can be separated into two broad categories: One
category is targeted for human users and often uses generic formats
or human readable documents, such as HTML or PDF. The other category
is structured information that followed some more formalized
description model, and is intended for consumption by machines, for
example for tools and code libraries.
In the context of this specification, the human-oriented variant is
referred to as "documentation", and the machine-oriented variant is
referred to as "description".
These two categories are not always mutually exclusive, as there are
formats that have been proposed that are intended for both human
consumption, and for interpretation by machine clients.
This specification places no constraints on the specific formats used
for either of those two categories. It simply allows publishers of a
Web service to make the documentation and/or the description of their
service discoverable, and defines two link relations that serve that
purpose.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
3. Web Services
"Web Services" or "Web APIs" (sometimes also referred to as "HTTP
API" or "REST API") are a way to expose information and services on
the Web. Following the principles of Web architecture, they expose
URI-identified resources, which are then accessed and transferred
using a specific representation. Many services use representations
that contain links, and often these links are typed links.
Using typed links, resources can identify relationships to other
resources. RFC 5988 [2] establishes a framework of well-known
registered link relation types, which are identified by simple
strings and registered in an IANA registry. Any resource that
supports typed links according to RFC 5988 can then use this
identifier to represent resource relationships on the Web without
having to re-invent the registered relation type.
In recent years, Web services and documentation and description
languages have gained popularity, due to the general popularity of
the Web as a platform for providing information and services.
However, the exact design documentation and description languages
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varies with a number of factors, such as the general application
domain, the preferred application data model, and the preferred
approach for exposing services.
It makes sense to provide service providers with a unified way to
link to service documentation and/or description. This link should
not make any assumptions about the provided type of documentation
and/or description, so that service providers can choose the ones
that best fit their services and needs.
3.1. Documenting Web Services
In the context of this specification, "documentation" refers to
information that is intended for human consumption. Typical formats
for this kind of documentation are HTML and PDF.
Documentation is often structured, but the exact kind of structure
depends on the structure of the service that is documented, as well
as on the specific way in which the documentation authors choose to
document it.
3.2. Describing Web Services
In the context of this specification, "description" refers to
information that is intended for machine consumption. Typical
formats for this are dictated by the technology underlying the
service itself, which means that in today's format landscape,
description formats exist in XML, JSON, RDF, and a variety of other
languages.
Descriptions are always structured, but the structuring principles
depend on the nature of the described service. For example, one of
the earlier service description approaches, the Web Services
Description Language (WSDL), uses "operations" as its core concept,
which are essentially identical to function calls, because the
underlying model is based on that of Remote Procedure Calls (RPC).
Other description languages for non-RPC approaches to services will
use different structuring approaches.
4. Link Relations for Web Services
In order to allow Web services to represent the relation of
individual resources to service documentation or description, this
specification introduces and registers two new link relation types.
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4.1. The service-doc Link Relation Type
The service-doc link relation type is used to represent the fact that
a resource is part of a bigger set of resources that are documented
at a specific URI. The target resource is expected to provide
documentation that is intended for human consumption.
4.2. The service-desc Link Relation Type
The service-desc link relation type is used to represent the fact
that a resource is part of a bigger set of resources that are
described at a specific URI. The target resource is expected to
provide a service description that is intended for machine
consumption. Very often, it is provided in a format that is consumed
by tools, code libraries, or similar components.
5. IANA Considerations
The link relation types below have been registered by IANA per
Section 6.2.1 of RFC 5988 [2]:
5.1. Link Relation Type: service-doc
Relation Name: service-doc
Description: Linking to service documentation that is primarily
intended for human consumption.
Reference: [[ This document ]]
5.2. Link Relation Type: service-desc
Relation Name: service-desc
Description: Linking to service description that is primarily
intended for consumption by machines.
Reference: [[ This document ]]
6. Security Considerations
...
7. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
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[2] Nottingham, M., "Web Linking", RFC 5988, October 2010.
Appendix A. Acknowledgements
Thanks for comments and suggestions provided by Mike Amundsen and
Darrell Miller
Author's Address
Erik Wilde
UC Berkeley
Email: dret@berkeley.edu
URI: http://dret.net/netdret/
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