M u s i c M L   a n   X M L   e x p e r i e n c e
 
  I n t r o d u c t i o n

a MusicML example (*)

(*) You need a jdk1.1.2 compatible browser like Netscape Communicator 4. Explorer 4 is not working at this moment because Microsoft shipped a previous release of their xml-parser with Explorer 4. Here you can find screenshots of the examples

Currently, the most popular markup language for the World Wide Web is HTML. Although HTML is extremely popular it lacks the possibility to extend it's functionality. Due to this shortcoming, the World Wide Web Consortium introduced a new language called XML. XML or Extensible Markup Language, is not a fixed defined markup language but more or less a Meta language strongly based on SGML.

Based on XML The Connection Factory defined it's own language specifically for sheet music called MusicML. Based on the definition of MusicML we wrote a MusicML browser in Java to be able to display our efforts.

Our goal was not to define a sheetmusic specific language, but to explore the capabilities and limits of XML.

 

M u s i c M L,   a   D T D   f o r  s h e e t m u s i c
XML documents basically have two components: the document type definition or DTD and the actual content itself. A DTD is a description of the document elements attributes and so on. For a complete description take a look at the XML specification issued by the World Wide Web Consortium at 10th February 1998.

A complete listing of the MusicML DTD can be found here.

A sheetmusic document according to MusicML has the following basic structure: 

    
     <sheetmusic>
       <musicrow size="two"> 
       </musicrow>
       <musicrow size="two">
       </musicrow>
     </sheetmusic>
In this example our piece of art has two lines. Every row has a double staff.

We divided a musicrow into logical pieces called a segment. A segment can contain several notes, chords grouped together between to vertical bars. Within a segment there are subsegments for every staff.

At the beginning of every musicrow there are several special elements like the Cleff which are defined for the entire musicrow. These special elements are grouped together in a so-called "entrysegment". Our music row has then the following structure: 

    
     <musicrow size="two">
       <entrysegment>
         <entrypart>       
         </entrypart>
         <entrypart>
         </entrypart>
       </entrysegment>
       <segment>
       </segment>
       <segment>
       </segment>
     </musicrow>
A typical two segment musicrow with two staffs and an entrypart for every staff will look like this:

Notes and rests can be grouped together within a chord or within a beam. A segment contains one or two subsegments (for every staff one) which itself contains several notes, rests, beams and/or chords.

example: 

    
    <segment>
      <subsegment position="one">
        <note beat="quarter" name="f"/> 
        <note beat="eighth"  name="g"/> 
        <chord>
          <note beat="sixteenth" name="a"/>
          <note beat="quarter" name="b"/>
          </chord>
        <rest size="half"/>
      </subsegment>
    </segment>
If you take a look at our complete DTD specification of MusicML you'll notice that a DTD specification is relatively easy to make and is an extremely short definition. This shows the exact strength of XML.

If you look more carefully at our DTD you'll notice one of the drawbacks of an XML DTD definition. It is strongly based on a hierarchical definition. This reflects the tension between strongly typed formats and great flexibility. For instance defining a DTD for curves from one note in the first subsegment to another note in the second subsegment is much more difficult.

 

B r o w s e r   i m p l e m e n t a t i o n
Based on the DTD specification, popular internet browsers can check wether a document they parse are well-formed. A browser however doesn't know how it should represent data formatted with elements defined in the DTD. Currently there is no standard available for representation (some work is done based on style sheets, but that wouldn't satisfy the needs for MusicML ( see http://www.w3.org/Style/). To overcome this problem you have two write your own browser. We wrote a MusicML browser based on Microsoft's XML parser which you can find at http://www.microsoft.com/workshop/author/xml/parser/ Based on this parser we wrote our browser as an Java applet which draws all the components on the screen.

Writing such a browser is relatively easy Java programming, feel free to take a look at the complete source.

A huge withdraw when you write applets that parse your XML document is that you cannot take advantage of the default formatting that is done by the browser itself. If you would implement something like: 

    
      <TABLE>
       <TR><TD><musicrow></musicrow></TD></TR>
       <TR><TD><musicrow></musicrow></TD></TR>
      </TABLE>
you are forced to write a representation of the table tag yourself. Therefore tight interaction between applets that implement a DTD and existing DTD implementations are needed.
 

C o n c l u s i o n
XML is a relatively simple Meta Language suitable for defining strongly typed based documents. It will fulfill the growing demand for better and more intelligent specification formats.

Implementing a browser for formats like MusicML is relatively easy in a language like Java. There is however need for a tight interaction between new and existing DTD implementations.

Please contact Jeroen van Rotterdam for more information on MusicML and/or XML.


The Connection Factory © 1997, 1998