This is question is actually a question to an answer from here, but since my rep is too low, I have no other option than to ask it like this. The question from that link goes like this:

I have a bibliography that mixes every reference type (mostly books and articles together). Now, I would love to be able to separate only the articles from the rest and display them under a separate bibliography subtitle, e.g. "Articles". Is this in any way possible?

someone called Zun answered the question that it is possible with biblatex, and a working example would be this:

    author       = {Bevel Lemelisk and Wilhuff Tarkin and Darth Vader and Darth Sidious},
    title        = {Death Star},
    howpublished = {Alderaan and Yavin 4},
    year         = {0 BBY}
    author       = {Bevel Lemelisk and Wilhuff Tarkin and Darth Vader and Darth Sidious},
    title        = {Death Star II},
    howpublished = {Endor},
    year         = {4 ABY}
    author       = {Abc, D.},
    title        = {The Letter Fantasies},
    year         = 1492,
    keywords     = {one}
    author       = {Efg, H.},
    title        = {Alphabet Soup},
    year         = 1942,
    keywords     = {two}
%   style=authoryear, % uncomment to display author-year
  not type=article
They first built \emph{Death Star}~\autocite{death-star}.

The design flaw was found in \autocite[Lemelisk et al., Chapter 3, p. 123][]{death-star}.

To address the flaw, they designed \emph{Death Star 2}~\autocite{death-star-2}
that featured many smaller diameter heat exhaust vents.

Read the letter fantasies \cite{abc} or stories from the a-soup \cite{efg}.
\printbibliography[heading=subbibliography,title={Other Sources},filter=other]

and this works flawlessly. As long as the entry-type is written with small letters. However, I use JabRef, and it formats my references with a capital letter, like @Online, @Book etc. In Zuns working example above, the entry @Book is with a capital letter. Try substituting @article with @Book. Suddenly it gives the error:

./untitled.tex:48: LaTeX Warning: Empty bibliography on input line 48.

Since all of my entries are with a capital letter, this is most unfortunate. Is there anything that can be done about this? Thank you for your time.

closed as unclear what you're asking by moewe, user31729, Mico, Paul Gaborit, Malipivo Apr 6 '15 at 11:06

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • Welcome to TeX.SX! Well, it's a warning only... – user31729 Jan 19 '15 at 22:14
  • Thank you :) Well, yes, it is a warning. But it is warning with the result that the bibliography that it warns about doesn't get printed, only the other bib, with the filter=other. – emilBeBri Jan 20 '15 at 0:56
  • 2
    I cannot reproduce your problem. I tried all lowercase @<whatever>, all uppercase, some uppercase and some lowercase; I switched the first @article to @Book. No problems (after running, of course, the full sequence of pdflatex, biber, pdflatex). You might need to elaborate. My versions: biblatex v2.9a and biber 1.9. – jon Jan 20 '15 at 3:47
  • It works like a charm here as well. (biblatex 2.9a with biber 1.9 on an up-to-date MikTeX.) What I noticed though is that your bibcheck construction is superfluous you can just use nottype=article instead of filter=other. – moewe Jan 20 '15 at 6:45
  • Okay, that is strange. Just updated texlive, I have biblatex 2.9a and biber 1.9 on my lubuntu 14.04 system. will try on a w7 machine later today, see if it's the same. Moewe: nice tip with the nottype instead, thank you! – emilBeBri Jan 20 '15 at 12:20