Constrained RESTful Environments (CoRE) Link Format
RFC 6690

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Internet Engineering Task Force (IETF)                         Z. Shelby
Request for Comments: 6690                                     Sensinode
Category: Standards Track                                    August 2012
ISSN: 2070-1721

          Constrained RESTful Environments (CoRE) Link Format

Abstract

   This specification defines Web Linking using a link format for use by
   constrained web servers to describe hosted resources, their
   attributes, and other relationships between links.  Based on the HTTP
   Link Header field defined in RFC 5988, the Constrained RESTful
   Environments (CoRE) Link Format is carried as a payload and is
   assigned an Internet media type.  "RESTful" refers to the
   Representational State Transfer (REST) architecture.  A well-known
   URI is defined as a default entry point for requesting the links
   hosted by a server.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6690.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Shelby                       Standards Track                    [Page 1]
RFC 6690                    CoRE Link Format                 August 2012

Table of Contents

   1. Introduction ....................................................3
      1.1. Web Linking in CoRE ........................................3
      1.2. Use Cases ..................................................4
           1.2.1. Discovery ...........................................4
           1.2.2. Resource Collections ................................5
           1.2.3. Resource Directory ..................................5
      1.3. Terminology ................................................6
   2. Link Format .....................................................6
      2.1. Target and Context URIs ....................................8
      2.2. Link Relations .............................................8
      2.3. Use of Anchors .............................................9
   3. CoRE Link Attributes ............................................9
      3.1. Resource Type 'rt' Attribute ...............................9
      3.2. Interface Description 'if' Attribute ......................10
      3.3. Maximum Size Estimate 'sz' Attribute ......................10
   4. Well-Known Interface ...........................................10
      4.1. Query Filtering ...........................................12
   5. Examples .......................................................13
   6. Security Considerations ........................................15
   7. IANA Considerations ............................................16
      7.1. Well-Known 'core' URI .....................................16
      7.2. New 'hosts' Relation Type .................................16
      7.3. New 'link-format' Internet Media Type .....................17
      7.4. Constrained RESTful Environments (CoRE) Parameters
           Registry ..................................................18
   8. Acknowledgments ................................................19
   9. References .....................................................20
      9.1. Normative References ......................................20
      9.2. Informative References ....................................20

Shelby                       Standards Track                    [Page 2]
RFC 6690                    CoRE Link Format                 August 2012

1.  Introduction

   The Constrained RESTful Environments (CoRE) realizes the
   Representational State Transfer (REST) architecture [REST] in a
   suitable form for the most constrained nodes (e.g., 8-bit
   microcontrollers with limited memory) and networks (e.g., IPv6 over
   Low-Power Wireless Personal Area Networks (6LoWPANs) [RFC4919]).
   CoRE is aimed at Machine-to-Machine (M2M) applications such as smart