MEI home
Excerpt from XSLT 2.0 Programmer's Reference, Third Edition:
A Scenario: Transforming Music
As an indication of how far XML has now penetrated,
Robin Cover's index of XML-
based application standards at
http://xml.coverpages.org/xmlApplications.html
today runs to over 580 entries. (The last one is
entitled Mind Reading Markup
Language, but as far as I can tell, all the other
entries are serious.)
I'll follow just one of these 580 lines, XML and
Music, which takes us to
http://xml.coverpages.org/xmlMusic.html. On this page
we find a list of no less
than 17 standards, proposals, or initiatives that use
XML for marking up music.
Some of this diversity is unnecessary, and many of
these initiatives will bear
little fruit. Even the names of the standards are
chaotic: there is a Music
Markup Language, a MusicML, a MusicXML, and a MusiXML,
all of which appear to be
quite unrelated. There are at least two really
serious contenders: the Music
Encoding Initiative (MEI) and the Standard Music
Description Language (SMDL).
The MEI derives its inspiration from the Text Encoding
Initiative, which is
widely used by the library community for creating
digital text archives, while
SMDL is related to the HyTime hypermedia standards and
takes into account
requirements such as the need to synchronize music
with video or with a lighting
script.
The diversity of standards is inevitable before the
industry can come up with a
standard that works for everyone. Without variety,
there can be no innovation
or experimentation. In fact, the likely outcome is
not a single standard, but a
collection of three or four different standards that
are optimized for different
needs. The different notations were invented with
different purposes in mind: a
markup language used by a publisher for printing sheet
music has different
requirements from the one designed to let you listen
to the music from a
browser.
For most of us, music may be fun, a diversion from
the world of work. But for
others, it is a very serious billion-dollar business.
Standards that make
information interchange in this business easier have
an enormous economic
impact. Whether you're interested in the music or the
money, we're not dealing
here with something that's trivial. So it shouldn't
be surprising that so much
effort is going into the process of creating standards
in this area.
In earlier editions of this book I introduced the
idea of using XSLT to
transform music as a theoretical possibility,
something to make my readers think
about the range of possibilities open for the
language. Today, it is no longer a
theoretical possibility -- people are actually doing
it.
With 17 different schemas for music in existence,
all with different strengths
and weaknesses (and fan clubs), there is a big need to
convert information from
one of these formats to any of the others. There is
also a need to convert
information from any of these formats to a printable
score or an audible
performance of the music, as well as a need to create
XML representations of
music from non-XML sources such as MIDI files. XSLT
has a role to play in all
of these conversions.
So you could use XSLT to:
* Convert music from one of these
representations to another, for example, from
MEI to SMDL.
* Convert music from any of these
representations into visual music notation, by
generating the XML-based vector
graphics format SVG.
* Play the music on a synthesizer,
by generating a MIDI (Musical Instrument
Digital Interface) file.
* Perform a musical transformation,
such as transposing the music into a
different key or extracting parts
for different instruments or voices.
* Extract the lyrics, into HTML or
into a text-only XML document.
* Capture music from non-XML formats
and translate it into XML (XSLT 2.0 is
especially useful here).
As you can see, XSLT is not just for converting XML
documents to HTML.
For some real examples of XSLT stylesheets used to
transform music, take a look
at a thesis written by Baron Schwartz at the
University of Virginia
(http://www.cs.virginia.edu/~bps7j/thesis/).
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