Session Date/Time: 12 Oct 2022 14:00

CORE

Summary

The CORE WG meeting focused primarily on proposals related to the URI scheme encoding within Concise Resource Identifiers (CRIs) defined in href documents. Discussion centered on the need for an IANA registry to manage negative integer assignments for URI schemes to ensure interoperability and extensibility. The second agenda item, concerning resource types for ANIMA documents, was deferred to the subsequent IoTops interim meeting to allow key participants to join.

Key Discussion Points

URI Scheme Encoding in CRIs (Marco)
- The href document's CDDL definition for CRIs allows URI schemes to be expressed as a text string or a negative integer.
- Currently, there is a hard-coded list of well-known schemes with associated negative integers, but no formal IANA registry exists for these assignments.
- The need for extensibility and interoperability for future schemes was highlighted, motivated by ongoing work such as the multicast notifications document (using TPI_SRV parameter with CRIs) and a CoAP option for server addressing.
- Proposal 1: Extend the initial hard-coded list of URI schemes to include existing coap+ schemes. This was generally considered straightforward.
- Proposal 2: Establish an IANA registry to track negative integer assignments for URI schemes.
  - Proposed registry structure would include the scheme name, assigned negative integer value (prioritizing 1-2 byte CBOR encodings for IoT use cases), and a reference to the defining document.
  - Policy for future registrations: Carson Borman raised concerns about interoperability. If new integer assignments are registered over time, older implementations might not recognize them, forcing senders to revert to text-string forms. He suggested that integer registration should ideally occur at the birth of a new URI scheme, within its defining document.
  - Esco questioned why negative integers are used (to avoid collision with positive integers in CRI syntax) and reiterated the interoperability challenge for older devices, even with "at birth" registration.
  - Christian Amsüss noted that CRIs are optimized for processing as-is, with conversion being a secondary concern, making extensibility a worthwhile compromise even with potential conversion difficulties.
  - Carson also mentioned potential issues with comparing CRIs when both text and integer forms exist. Christian responded that resource identity often requires scheme-specific normalization, which general tools cannot provide anyway.
  - A sense of those present indicated that exploring the registry direction, despite its complexities, is valuable to avoid a "second-class system" for newer URIs.
Categorization of Scheme Importance (Carson)
- Carson outlined a categorization approach for the wiki (which he had already initiated) based on the CBOR encoding length of negative integers: "1+0" for short identifiers (e.g., -1 to -24), "1+1" for the next range (e.g., -25 to -256), and "1+2" for larger numbers. This helps prioritize schemes for compact encoding.
- Carson also mentioned that the Bluetooth SIG had undertaken a similar exercise of mapping schemes to 16-bit numbers, and offered to find a pointer to that work.
ANIMA Resource Type Discussion
- The discussion on the resource type target attribute for ANIMA documents was postponed. This was done to accommodate Michael, a key participant, who was in another meeting and would be available at the subsequent IoTops interim meeting.
- Esco briefly asked about the resource-type registration for the joint-proxy document, noting existing doubts about its appropriateness. Carson confirmed that the primary doubt is whether the registered item is truly a resource type, and this discussion would proceed in IoTops.

Decisions and Action Items

Decision: The working group will proceed with exploring the introduction of an IANA registry for negative integer assignments to URI schemes within CRIs.
Action Item: Marco to draft new text for Proposal 2 (establishing the IANA registry and defining policies for future registrations) for discussion in a future submission.
Action Item: A wiki page will be used to collect and categorize URI schemes suitable for inclusion in the initial registry population (Proposal 1).
Action Item: Carson Borman to provide a pointer to the Bluetooth SIG's similar work on URI scheme mapping.
Decision: The discussion regarding the resource type target attribute for ANIMA documents is deferred to the IoTops interim meeting.

Next Steps

Review and discuss the new draft text for the CRI URI scheme registry proposal.
Populate and review the wiki page for initial URI scheme candidates for negative integer assignment.
The ANIMA-related discussion will be held at the upcoming IoTops interim meeting.