Spectrum version 1.2 Erratum 1: VOCLASS example

Author: Mark Cresitello-Dittmar

Date last changed: 2025-11-18

Date accepted:

Rationale

The standard has an inconsistent value expressed for the VOCLASS keyword throughout the document. The keyword occurs 4 times in the document, and in each case, the associated value string follows a different formatting pattern. For the keyword to be useful in describing the standard to which the FITS file conforms, the string really MUST have a fixed structure. Unfortunately, while the keyword is mandatory (see Table 1), the document does not fix the value string to a particular value or pattern.

We propose to unify the string representation within the document, and add text to recommend how users should interpret the value (ignoring minor version). This is in keeping with similar quantities in the VO and does not introduce any backward compatibility issues.

Additionaly, the text describes the keyword as 'new', and while it may have been new in the initial version, it is not new in subsequent versions. The phrasing is ambiguous and should be replaced with a more concrete statement.

Erratum Content

This Erratum proposes to make the following changes to consistently show the preferred version string. We selected the value from §3.7 Data Model Fields, Table 1, 'Spectrum-1.0', as being that 'preferred' string.

Spectrum 1.2

§9.1, pg. 74. VOCLASS Keyword
Replace the text:

We add a new keyword VOCLASS to describe the VO object represented by the FITS table. The value of VOCLASS should be ’SPECTRUM 1.00’

We define the keyword VOCLASS to describe the VO object represented by the FITS table. The value of VOCLASS should be ’Spectrum-1.0’. 
For determining compatibility, one should perform a case-sensitive match to the string, ignoring the minor version (e.g. "Spectrum-1."). 

§9.1, Table F.1, pg. 76. FITS keywords for VO Spectrum
The 'Value if fixed' entry for the VOCLASS record from

'SPECTRUM 1.0'

'Spectrum-1.0'

§9.4, pg. 82. An instance example
The value of the keyword VOCLASS from

'Spectrum V1.0'

'Spectrum-1.0'

Impact Assessment

The keyword value has no fixed specification, so there can be no impact on modifying the examples provided in the document. However, by unifying the strings in the standard, it sets a pattern of expectation, which will encourage more consistency in general usage.