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<H1><A NAME="SECTION01110000000000000000">
Babel Facilitates Language Interoperability</A>
</H1>
Babel was conceived, designed, and built to solve a problem; namely,
to make scientific software libraries equally
accessible from all of the standard languages. Hence, its goal is language
interoperability. The vision goes far beyond
calling BLAS<A NAME="tex2html6"
HREF="footnode.html#foot535"><SUP><SPAN CLASS="arabic">2</SPAN>.<SPAN CLASS="arabic">1</SPAN></SUP></A>implemented in FORTRAN 77 from a C program. At its heart, Babel
lets programmers use their tool of choice in developing
complete applications using components implemented in one or more
distinct programming languages.
<P>
For instance<A NAME="536"></A>, let us say that an application scientist
is running a sophisticated C++ code from a Python scripting
environment. This can already be easily accomplished with
technologies like SWIG<A NAME="537"></A>. Now let's say that the simulation
is showing some erratic behavior and the application scientist
wants to extend the <TT>ConvergenceCheck</TT> class to also report some
information to a log file. Let's also assume that this
application scientist doesn't want to write a new C++ class
much less rewrite the current application. What this individual
wants to do is derive and utilize a new class in Python from the C++
<TT>ConvergenceCheck</TT> class.
Thus, the C++ simulation code will now have to invoke a
method on a class implemented in Python, which then dispatches
back to the C++ base class after doing its additional logging. This
cannot be done in SWIG because SWIG does not support calls from C++ to
Python, only from Python to C++.
This is an example of a capability that Babel provides that is
outside the scope of SWIG.
<P>
<DIV ALIGN="CENTER"><A NAME="fig:intro:currentlanginterop"></A><A NAME="545"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 1.1:</STRONG>
Language Interoperability Using Current Technology.</CAPTION>
<TR><TD><A NAME="541"></A>
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<IMG
WIDTH="452" HEIGHT="296" ALIGN="BOTTOM" BORDER="0"
SRC="img4.png"
ALT="\includegraphics[width=4in]{common/figs/CurrentLangInterop}">
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<P>
Figure <A HREF="#fig:intro:currentlanginterop">1.1</A> lists many of
the primary languages that are of interest to scientific
simulation software developers and users. The good news
is that there is a path from each language to every other;
meaning that calling from one to another is possible.
However, the technologies to get from one language to
another vary widely, are fraught with pitfalls, and may require
calling through a completely different language.
<P>
Babel works by providing the technology to define and support the
multi-language interoperation of a common subset of functionality
through programming language-neutral interface specifications.
See Fig. <A HREF="#fig:intro:babellanginterop">1.2</A>
to see a graphical representation of the supported languages.
It is important to note that this common functionality subset
is <SPAN CLASS="textit">far</SPAN> from a lowest common denominator solution in that
Babel actually adds functionality when it is lacking in the host language.
<P>
<DIV ALIGN="CENTER"><A NAME="fig:intro:babellanginterop"></A><A NAME="555"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 1.2:</STRONG>
Language Interoperability Using Babel.</CAPTION>
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