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@node problem-statement 
@unnumberedsec Designing notation software: how not to do it

It would be nice if notation software didn't need any babysitting to
produce acceptable output. 

Our goal with @emph{LilyPond} was to write such a system: a program
that will produce beautiful music ("engraving") automatically.

At first sight, music notation follows a straightforward hierarchical
pattern.  Consider the example below, with two staves containing two
measures.

@sourceimage{naive-notation,,,.png}

Isn't writing software all about finding hierarchies and modeling the
real world in terms of trees? In the view of a naive programmer, the
above fragment of notation is easily abstracted to a nested set of
boxes

@sourceimage{naive-notation-uml,,,.png}

It's easy to follow this model when writing software.  It's obvious
how to store this data in memory, and writing on disk can be easily
mirrored. In an XML-file you could write something like

@verbatim

  <score>
    <staff>
      <measure id="1">
         <chord length="1/2">
	   <pitch name="c">
         </chord>
         <chord>
	 
	 ....
      </measure>
    </staff>
  </score>

@end verbatim

In short, this model is obvious, simple and neat.  It's the format
used by a lot software. Unfortunately, it's also wrong.  The
hierarchical representation works for a lot of simpler music, but it
falls apart for advanced use. Consider the following example:

@sourceimage{nonnaive-notation,,,.png}

In this example, several assumptions of the previous model are
violated: staves start and stop at will, voices jump around between
staves, and sometimes span two staves.

Music notation is really different from music itself. Notation is an
intricate symbolic diagramming language for visualizing an often much
simpler musical concept. Hence, software should reflect that separation.

@divClass{float-right}
Next: @ref{divide-and-conquer,Divide and conqueror},
a blue print for automated notation
@divEnd