Simple Cone Search version 1.03 Erratum 1: <INFO name="Error"> uniqueness clarification

Author: Marco Molinaro

Date last changed: 2017-10-06

Date accepted: 2018-02-22

Rationale

Most Cone Search services at the time of writing (2017) fail validation because the query response, in case of error, contains additional <INFO> elements alongside the required <INFO name="Error"> one to identify it as an error response.

This is probably due to a strict interpretation of the second paragraph in §2.3 of the Cone Search specification version 1.03, where it is stated that the error VOTable response must contain a single INFO element with name ="Error".

VOTable, however, allows multiple generic INFO elements to be child of the required VOTABLE or RESOURCE parents, to leave space to convey various informative tokens together.

Relaxing the interpretation of the recommendation sentence will allow an improvement in validation clearness without affecting any other services or client applications.

Erratum Content

This Erratum proposes to change, in §2.3 of Simple Cone Search - Version 1.03 the sentence:

In the case of error, the service MUST respond with a VOTable that contains a single PARAM element 
or a single INFO element with name="Error", where the corresponding value attribute should contain 
some explanation of the nature of the error.

with the following one:

In the case of error, the service MUST respond with a VOTable that contains a PARAM element or 
an INFO element with name="Error", where the corresponding value attribute should contain some 
explanation of the nature of the error. No other PARAM or INFO element in the response can be 
present having name="Error" set, but additional INFO and PARAM elements with the name parameter 
set to a different value are allowed.

In this way the usage of multiple INFO elements in an error response is allowed without affecting current Cone Search v. 1.03 error response behaviour.

Impact Assessment

The proposed change should not affect the way clients detect error response from cone searches and is meant to allow current behaviour of most of the existing cone search services already properly working. Thus, this erratum should only affect validation engines, that is actually the goal of the erratum itself, trying to clear up the view on non compliant cone search services removing from non-compliance those that simply provide extra information in their error responses.