SLAP v1.0 Erratum 1: No longer require an invalid UCD

Author: Markus Demleitner

Date last changed: 2022-03-16

Date accepted: 2022-04-20


SLAP version 1.0 requires the UCD em.line on the column with the utype ssldm:Line.title. The current UCD list, however, marks the em.line atom as S, meaning it cannot stand in the first position of a full UCD. While its current definition (“Designation of major atomic lines”) does perhaps not fully justify that constraint, after some deliberation it seems preferable to resolve the contradiction between UCD 1.4 and SLAP 1.0 by updating the UCD in SLAP.

SLAP version 1.0 contains another invalid UCDs in appendix B (em.line; Since to our knowledge nobody intends to implement appendix B-type services and the material has additional problems (e.g., utypes without obvious counterparts in SSLDM), we opt to not try to repair these deficiencies and rather deprecate the appendix.

Erratum Content

(1) In section 6.1 (Standard output fields), PDF page 16, replace

Exactly one field MUST have utype=”ssldm:Line.title”, with datatype="char" arraysize="*" and ucd=”em.line”, containing a small description identifying the line.


Exactly one field MUST have utype=”ssldm:Line.title”, with datatype="char" arraysize="*" and ucd=”;em.line”, containing a small description identifying the line.

(2) In appendix B (SLAP services for uncorrected and unidentified lines), on PDF page 21 add before the section content

The material in this section is deprecated and has several issues (invalid UCDs, undefined utypes). Implementors considering implementing SLAP for uncorrected and unidentified lines should contact the IVOA DAL Working Group at

(3) In appendix C (SLAP valid response example), PDF page 24, replace

<FIELD ucd="em.line" name="IDENTIFICATION" utype="ldm:Line.title" datatype="char" arraysize="*"/>


<FIELD ucd=";em.line" name="IDENTIFICATION" utype="ldm:Line.title" datatype="char" arraysize="*"/>

(4) In appendx D (SLAP data model summary), PDF page 25, replace "em.line" in the UCD column of the row for the utype ssldm:Line.title with ";em.line".

Impact Assessment

SSAP clients do not identify fields by UCDs and hence are unaffected by this change. Clients relying on UCDs to determine how to treat individual columns may profit from the somewhat improved annotation.

Most importantly, valid SLAP services will no longer raise errors in UCD validation.

Topic revision: r2 - 2022-04-25 - MarcoMolinaro
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