Conferences as publication venues – black and white or is there a grey or third way?

There are two ways of treating conferences that are commonly mentioned on this site:

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  Conferences are publication venues for papers (or similar). Submissions will be subjected to a serious peer review, are citable as evidence, and are a relevant achievement. Submitting the same material to two different conferences or a journal and a conference would be considered self-plagiarism.

  
  

  This applies to computer science and engineering (or at least some subfields thereof) – for details, see: Is the status of conference publications in Computer Science really absolutely unique?

  
  


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  Conferences are not publication venues. The material presented there is typically also published in journals, books, and similar – but this process is not tied to the conference; it may occur before the conference, later, or even not at all. Submissions are only subjected to minimal review¹, are not citable as evidence, and not considered a big achievement. Participating in conferences is still considered important though. It is common that authors present the same material at different conferences.

  
  

  This applies to the majority of fields.

  
  

  ^{¹ to weed out utter crap or to decide what should be a talk and what a poster}

  
  
  

In light of this Meta question, I am interested whether the above two cases are the only two. To me, it would not be surprising if this actually is the case, as the two categories have a self-preserving mechanisms. For example, for a conference belonging to the first category, weakening the criteria for submission would usually be a bad move. On the other hand, I am very well aware that I do not know every field’s customs. Hence, I am asking: Are there conferences that hold a status not described by the two categories above? Please answer only if you can name and describe such a conference – if this question remains unanswered, this would be an acceptable and meaningful outcome.

Note that this is only about what is submitted directly to the conference for the purpose of being presented there. Whether articles corresponding to the presented material will be collected for a book, special issue of a journal, or other form of proceedings – be it with separate peer review or not – is irrelevant for the purposes of this question.

Answer

Yes, there's a third type where a single conference uses multiple submission categories, and submissions to one category are thoroughly reviewed and published as papers in the proceedings, whereas submissions to the other category only appear with short abstracts in the conference booklet or similar, and may also be restricted to specific sessions (such as poster sessions).

I know such conferences in mathematical oriented engineering fields. As just one example, I can mention the Vienna International Conference on Mathematical Modelling. If you look at their call for papers, they have a category "Full Contribution", where full papers are solicited, to be published in the formal proceedings after the review and presentation. But they also have categories "Discussion Contribution" and "Student Contribution", where only abstracts are submitted, and there's no formal publication associated with the submission.

There are other conferences in the same field which make this distinction as well within their submission categories.