Subbibliography with roman numbers and Biblatex

Question

I am currently working on a thesis, where I have to use one subbibliography. This works pretty well with Biblatex and keywords. Now my faculty wants to have this subbibliography (and only this) to be numbered with large roman numbers. The main bibliography at the end of the document should still be sorted alphabetically after the first authors.

Is there a way to do this or do you have a pointer I missed so far?

This is a MWE:

\documentclass{scrreprt}   
\usepackage{filecontents}
\usepackage[%
 natbib=true,%
 citestyle=authoryear,%
 bibstyle=authoryear,%
 backend=bibtex,%
 ]{biblatex}

\defbibfilter{subbib}{keyword=subbib} % Authors publications must have set keyword to "own"
\begin{filecontents}{test.bib}
 @article{hoek2008b,
   author = {Hoek, K. S. and Schlegel, N. C.},
   title = {Novel MITF targets identified using a two-step DNA microarray strategy},
   journal = {Pigment Cell Melanoma Res},
   volume = {21},
   number = {6},
   pages = {665-76},
   keywords = {subbib},
   year = {2008}
}
 @article{hou2008,
   author = {Hou, L. and Pavan, W. J.},
   title = {Transcriptional and signaling regulation in neural crest stem cell-derived melanocyte development: do all roads lead to Mitf?},
   journal = {Cell Res},
   keywords = {subbib},
   year = {2008}
}

 @article{alister2013,
   author = {Alister, J.A.},
   title = {MITF from missense to malady},
   journal = {Pigment Cell Melanoma Res},
   keywords = {pigment},
   year = {2013}
}
 \end{filecontents}

 \addbibresource{test.bib}
\begin{document}
\tableofcontents
 \chapter{This is a test chapter}
 This is only test text.
  \printbibliography[title={Subbibliography}, filter=subbib]

 \chapter{Test for bibliography}
  This is a test to cite \parencite{alister2013} and also cite\parencite{hou2008} which has also been 
  described by \textcite{hoek2008b}.

  \printbibliography[title=References]
\end{document} 

I want to have the subbibliography numbered with roman numbers, the references at the end should be author-year.

Answer 1

I have got an answer to the question in a german tex community, which looks like the following:

It bases on the thread "Two bibliographies with two different styles in the same document" from tex.sx and defines new environment for the two bibliographies. Additionally it uses \DeclareFieldFormat to introduce a new format for roman numbers. To get the literature cited without problems, a refsection is used in which only my own literature is cited.

Code:

\documentclass{article}
\usepackage[citestyle=authoryear, frontend=bibtex8]{biblatex}
\DeclareFieldFormat{Roman}{\RN{#1}}
% The following definition is copied from numeric.bbx
\defbibenvironment{roman-numerals}
  {\list
     {\printtext[labelnumberwidth]{%
    \printfield{prefixnumber}%
    \printfield[Roman]{labelnumber}}}
     {\setlength{\labelwidth}{\labelnumberwidth}%
      \setlength{\leftmargin}{\labelwidth}%
      \setlength{\labelsep}{\biblabelsep}%
      \addtolength{\leftmargin}{\labelsep}%
      \setlength{\itemsep}{\bibitemsep}%
      \setlength{\parsep}{\bibparsep}}%
      \renewcommand*{\makelabel}[1]{\hss##1}}
  {\endlist}
  {\item}

% The following definition is copied from authortitle.bbx/authoryear.bbx
\defbibenvironment{nolabelbib}
  {\list
     {}
     {\setlength{\leftmargin}{\bibhang}%
      \setlength{\itemindent}{-\leftmargin}%
      \setlength{\itemsep}{\bibitemsep}%
      \setlength{\parsep}{\bibparsep}}}
  {\endlist}
  {\item}
\defbibfilter{subbib}{keyword=subbib}
\begin{filecontents}{\jobname.bib}
@misc{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
}
@misc{B02,
  author = {Buthor, B.},
  year = {2002},
  title = {Bravo},
  keywords = {subbib},
}
@misc{C03,
  author = {Cuthor, C.},
  year = {2003},
  title = {Charlie},
  keywords = {subbib},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\begin{refsection}
\nocite{B02, C03}
\printbibliography[title={Subbibliography}, keyword=subbib, env=roman-numerals]
\end{refsection}
Some text \autocite{A01,B02}.
\printbibliography[env=nolabelbib, title=References]
\end{document}