OPeNDAP Link Type

From Earth Science Information Partners (ESIP)

DCP-i: OPeNDAP Link 'rel' Attribute Value

  • Progress:
  1. Submitted on: 4/28/11
  2. Review period: N/A
  3. Revision: N/A
  4. Vote: N/A
  5. Final review: N/A
  6. Ratified: N/A
  7. Rejected: N/A
  • Facilitator: ?
  • Authors: ?


The Discovery Response Format (v1.1) includes the following values for the "rel" attribute on the <link> element.

Link type Description Default data link. Data Casting Granules. OpenSearch Granules response. Appropriate for smaller browse images. See following for alternate browse links. Default documentation. See following for alternate documentation links. Data, collection, and service metadata. Data Casting Collection. Not for OpenSearch Collection response which uses OSDD instead. Service Casting. Micro-articles of natural phenomenon. Feed of various feeds. Enables hierarchy of feeds.

In addition to the "rel" attribute specifying what a URL addresses, there is also a "type" attribute. The values for the "type" attribute are recommended to be mime-type values, but this is not enforced.

In light of this, it may be possible that data providers will have multiple URLs that point to downloadable data. In each of these cases, the "rel" attribute value would be "". A specific use case would be a granule that has a direct download link to the HDF file and also a download link to an OPeNDAP service. With only a single "rel" attribute value, clients and/or users are unable to distinguish between download link types.

The scope of this DCP is constrained to resolving this issue for OPeNDAP URLs. Other data download link types should be included in separate DCPS.

Proposed Solution

It is a proposed that a new "rel" attribute value be added specifically for OPeNDAP download URLs. Possible values (thanks to Mr. Lynnes) are:


Rationale for the Solution

A separate "rel" attribute value will provide a clear designation regarding what type of data or service a URL is referencing. ECHO is specifically interested in this solution in light of efforts to incorporate OPeNDAP URLs into provider metadata and other work with the EOSDIS Service Interface and GESDISC's Simple Subset Wizard.

The rationale for the specific value is less defined. It is assumed that discussion within the ESIP cluster will define the rationale for the chosen value.