In support of the accepted answer, I just wanted to add a test file for reference.
Basically, a bibliography can be compiled either with "plain" bibtex, or with biblatex with bibtex backend, or with biblatex with biber backend. In all three cases a .bbl file is produced - but in all three cases the format of the .bbl file is different!
\bibitem occurs in the .bbl file only when "plain" bibtex is used. (biblatex uses \entry, \strng, \field etc)
In this particular test file, there is no difference in (pdf) output between backends when biblatex is used - but there is a slight difference (e.g. quotation marks and capitalization in title, the "In:" ...) between the "plain" bibtex (left) and biblatex outputs (right, click for full res):

The test file is this, let's call it bibtest.tex:
\documentclass{article}
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@book{smith1,
author={John Smith and Mike Someone},
title={The book with a very very very very very long title},
year={2006},
location={New York},
publisher={Publisher},
}
@article{audactor2005pflanzen,
title = {Wie Pflanzen hören... die Geheimnisse der Sonobotanik},
author = {Prof. Dr. Hortensia Audactor},
journal = {Draft: \url{http://www.inventionen.de/2005/sonobotanik.html}},
year = {2005}
}
\end{filecontents*}
\usepackage[utf8]{inputenx}
\usepackage[T1]{fontenc}
\usepackage{hyperref}
% btype: 1: bibtex ; 2: biblatex+bibtex ; 3: biblatex+biber
\ifx\btype\undefined %
\def\btype{1} %
\fi
\ifnum\btype=2 %
\usepackage[url=true,backend=bibtex]{biblatex} %
\bibliography{\jobname} %
\fi
\ifnum\btype=3 %
\usepackage[url=true,backend=biber]{biblatex} %
\bibliography{\jobname} %
\fi
\begin{document}
Just testing the bibliography: the book \cite{smith1}, and the article \cite{audactor2005pflanzen}.
\ifnum\btype=1 %
\bibliographystyle{plain} % Style BST file
\bibliography{\jobname} % Bibliography file ('*.bib' )
\else % \btype=2 or 3
%\bibliography{\jobname} % for biblatex, only in preamble!
\printbibliography %
\fi
\end{document}
% clean: rm $(ls --hide=*.tex)
Here are the steps and results of the compilation:
1. plain bibtex
# \btype=1
pdflatex bibtest.tex # creates: .aux, .bib, .log, .out, .pdf
bibtex bibtest # creates: .bbl, .blg
pdflatex bibtest.tex
pdflatex bibtest.tex
The produced bibtest.bbl file is:
\begin{thebibliography}{1}
\bibitem{audactor2005pflanzen}
Prof. Dr.~Hortensia Audactor.
\newblock Wie pflanzen hören... die geheimnisse der sonobotanik.
\newblock {\em Draft: \url{http://www.inventionen.de/2005/sonobotanik.html}},
2005.
\bibitem{smith1}
John Smith and Mike Someone.
\newblock {\em The book with a very very very very very long title}.
\newblock Publisher, 2006.
\end{thebibliography}
2. biblatex and backend bibtex
pdflatex "\def\btype{2}\input{bibtest.tex}" # creates: .aux, .bib, -blx.bib, .log, .out, .pdf, .run.xml
bibtex bibtest # creates: .bbl, .blg
pdflatex "\def\btype{2}\input{bibtest.tex}" # biblatex Warning: Data encoding is 'utf8'. Use backend=biber.
The produced bibtest.bbl file is:
% $ biblatex auxiliary file $
% $ biblatex version 1.7 $
% Do not modify the above lines!
%
% This is an auxiliary file used by the 'biblatex' package.
% This file may safely be deleted. It will be recreated as
% required.
%
\begingroup
\makeatletter
\@ifundefined{ver@biblatex.sty}
{\@latex@error
{Missing 'biblatex' package}
{The bibliography requires the 'biblatex' package.}
\aftergroup\endinput}
{}
\endgroup
\entry{audactor2005pflanzen}{article}{}
\name{author}{1}{}{%
{{}%
{Audactor}{A.}%
{Prof. Dr.~Hortensia}{P.~D.~H.}%
{}{}%
{}{}}%
}
\strng{namehash}{APDH1}
\strng{fullhash}{APDH1}
\field{sortinit}{A}
\field{title}{Wie Pflanzen hören... die Geheimnisse der Sonobotanik}
\field{journaltitle}{Draft:
\url{http://www.inventionen.de/2005/sonobotanik.html}}
\field{year}{2005}
\endentry
\entry{smith1}{book}{}
\name{author}{2}{}{%
{{}%
{Smith}{S.}%
{John}{J.}%
{}{}%
{}{}}%
{{}%
{Someone}{S.}%
{Mike}{M.}%
{}{}%
{}{}}%
}
\list{publisher}{1}{%
{Publisher}%
}
\strng{namehash}{SJSM1}
\strng{fullhash}{SJSM1}
\field{sortinit}{S}
\field{title}{The book with a very very very very very long title}
\list{location}{1}{%
{New York}%
}
\field{year}{2006}
\endentry
\lossort
\endlossort
\endinput
2. biblatex and backend biber
pdflatex "\def\btype{3}\input{bibtest.tex}" # creates: .aux, .bcf, .bib, .log, .out, .pdf, .run.xml
LANG=en_US.UTF-8 biber bibtest # creates: .bbl, .blg
pdflatex "\def\btype{3}\input{bibtest.tex}"
The produced bibtest.bbl file is:
% $ biblatex auxiliary file $
% $ biblatex version 1.7 $
% $ biber version 0.9.9 $
% Do not modify the above lines!
%
% This is an auxiliary file used by the 'biblatex' package.
% This file may safely be deleted. It will be recreated by
% biber or bibtex as required.
%
\begingroup
\makeatletter
\@ifundefined{ver@biblatex.sty}
{\@latex@error
{Missing 'biblatex' package}
{The bibliography requires the 'biblatex' package.}
\aftergroup\endinput}
{}
\endgroup
\refsection{0}
\entry{audactor2005pflanzen}{article}{}
\name{labelname}{1}{}{%
{{hash=1d15dc798dec1fd384ab9a796ebab9f5}{Audactor}{A\bibinitperiod}{Prof.\bibnamedelimi Dr.\bibnamedelimi Hortensia}{P\bibinitperiod\bibinitdelim D\bibinitperiod\bibinitdelim H\bibinitperiod}{}{}{}{}}%
}
\name{author}{1}{}{%
{{hash=1d15dc798dec1fd384ab9a796ebab9f5}{Audactor}{A\bibinitperiod}{Prof.\bibnamedelimi Dr.\bibnamedelimi Hortensia}{P\bibinitperiod\bibinitdelim D\bibinitperiod\bibinitdelim H\bibinitperiod}{}{}{}{}}%
}
\strng{namehash}{1d15dc798dec1fd384ab9a796ebab9f5}
\strng{fullhash}{1d15dc798dec1fd384ab9a796ebab9f5}
\field{sortinit}{A}
\field{journaltitle}{Draft: \url{http://www.inventionen.de/2005/sonobotanik.html}}
\field{title}{Wie Pflanzen hören... die Geheimnisse der Sonobotanik}
\field{year}{2005}
\endentry
\entry{smith1}{book}{}
\name{labelname}{2}{}{%
{{hash=5d0ddda3a367ceb26fbaeca02e391c22}{Smith}{S\bibinitperiod}{John}{J\bibinitperiod}{}{}{}{}}%
{{hash=51e9bdc59ecfdbdb5cf9ee7ecd37d83f}{Someone}{S\bibinitperiod}{Mike}{M\bibinitperiod}{}{}{}{}}%
}
\name{author}{2}{}{%
{{hash=5d0ddda3a367ceb26fbaeca02e391c22}{Smith}{S\bibinitperiod}{John}{J\bibinitperiod}{}{}{}{}}%
{{hash=51e9bdc59ecfdbdb5cf9ee7ecd37d83f}{Someone}{S\bibinitperiod}{Mike}{M\bibinitperiod}{}{}{}{}}%
}
\list{location}{1}{%
{New York}%
}
\list{publisher}{1}{%
{Publisher}%
}
\strng{namehash}{bdb6caeb721d71d176dbc1db99a48c69}
\strng{fullhash}{bdb6caeb721d71d176dbc1db99a48c69}
\field{sortinit}{S}
\field{title}{The book with a very very very very very long title}
\field{year}{2006}
\endentry
\endrefsection
\endinput
\bibitemstructure and I dont think that's what the other code does. I did manage to convert mybiblatexintobibitembut cannot deal with the reference in the text.... Any clue? – Xochitl C. Jan 20 '14 at 09:19