Introduction to MEI and XML Schema

The Music Encoding Initiative (MEI) is a framework for representing music notation in a structured, machine-readable way. It is based on XML, which means that MEI files are plain text files with a clear hierarchical structure.

For musicologists, this is useful because it allows us to:

• describe notation precisely
• document editorial decisions
• process musical data computationally
• validate encodings automatically
• exchange data between tools and projects

For the official documentation, see the MEI Guidelines: Introduction.

You can think of MEI like this:

• music notation = the thing we want to describe
• XML = the language used to write that description
• schema = the rulebook that says what is allowed
• MEI = a music-specific XML vocabulary

So MEI is not „just XML“. It is a specialized XML language for music notation.

XML stands for eXtensible Markup Language.

For absolute beginners, the easiest way to understand XML is:

XML is a way of writing structured information using labeled elements.

Example:

<note pname="c" oct="4" dur="4"/>

This means:

• the element is called note
• it has a pitch name: c
• it has an octave: 4
• it has a duration: 4

XML is made of elements and attributes.

Elements are the named building blocks, for example:

• <measure>
• <staff>
• <layer>
• <note>
• <rest>

Some elements have opening and closing tags:

<measure>
  ...
</measure>

Some are empty and written in a short form:

<note pname="c" oct="4" dur="4"/>

Attributes add information to an element.

Example:

<note pname="f" oct="5" dur="2"/>

Here:

• pname = pitch name
• oct = octave
• dur = duration

A useful beginner distinction is:

• element = what kind of thing this is
• attribute = extra information about that thing

A schema is a set of rules for an XML language.

For beginners, the most useful mental model is:

A schema is like a grammar or rulebook for XML.

It tells us things like:

• which elements are allowed
• where they are allowed
• which attributes they may have
• which values are valid

Without a schema, you could write almost anything. With a schema, a computer can check whether your file follows the rules.

So a schema helps answer questions like:

• Is a <note> allowed here?
• May a <measure> contain a <staff>?
• Is pname=„h“ valid?
• Does this link point to an existing element?

For editorial and research work, schema is important because it helps us avoid errors.

It can catch problems such as:

• invalid element names
• misplaced elements
• missing required information
• invalid attribute values
• broken references

So schema validation is one of the reasons MEI is useful in scholarly work:

• it makes encodings more consistent
• it makes collaboration safer
• it improves interoperability

MEI is an XML-based encoding framework. Its rules are not invented separately by each project. Instead, MEI defines a structured vocabulary for music notation.

For beginners, the important point is simply:

• XML gives the syntax
• MEI gives the music-specific elements and attributes
• the schema checks whether the encoding is valid

<measure n="1">
  <staff n="1">
    <layer n="1">
      <note pname="c" oct="4" dur="4"/>
      <note pname="d" oct="4" dur="4"/>
      <note pname="e" oct="4" dur="4"/>
      <note pname="f" oct="4" dur="4"/>
    </layer>
  </staff>
</measure>

You can read this as:

• one measure
• containing one staff
• containing one layer
• containing four notes

A very common beginner structure is:

score
└── section
    └── measure
        └── staff
            └── layer
                └── note / rest / chord / etc.

A practical way to understand this is:

• score = the whole musical object
• measure = one bar
• staff = one staff in that measure
• layer = one musical stream or voice on that staff
• note = one event inside that layer

Two important elements are:

• <scoreDef>
• <staffDef>

These do not usually encode the individual notes themselves. Instead, they define the notational environment.

You can think of them like this:

• scoreDef = settings that can apply to the whole score
• staffDef = settings for a particular staff

These are often used for things such as:

• clef
• key signature
• meter
• staff properties

A useful beginner idea is that these elements often act like defaults: they remain in force until they are changed later.

In Common Music Notation (CMN), MEI defines a note through three basic parameters:

• pname = pitch name
• oct = octave
• dur = duration

Example:

<note pname="c" oct="4" dur="4"/>

This means:

• pitch name = C
• octave = 4
• duration = quarter note

Pitch in beginner MEI examples is usually encoded with:

• pname
• oct

Example:

<note pname="g" oct="5" dur="2"/>

This means G5 as a half note.

So the basic pitch information is split into:

• note name
• octave

A written accidental can be encoded with the accid attribute.

Example:

<note pname="f" oct="4" dur="4" accid="s"/>

This means an F sharp quarter note.

For beginners, the important idea is:

• pname gives the diatonic pitch name
• accid adds the written accidental

In other words:

• pname=„f“ = F
• accid=„s“ = sharp sign written on that note

Duration is encoded with dur.

Common beginner values include:

• 1 = whole note
• 2 = half note
• 4 = quarter note
• 8 = eighth note

Example:

<note pname="a" oct="4" dur="8"/>

Measures are encoded with <measure>.

Example:

<measure n="12">
  ...
</measure>

Here:

• measure identifies the bar
• n stores the measure number or label

The measure acts as a container for the musical material belonging to that bar.

Inside a measure, notes are usually organized through:

• <staff>
• <layer>

Example:

<measure n="1">
  <staff n="1">
    <layer n="1">
      <note pname="c" oct="4" dur="4"/>
    </layer>
  </staff>
</measure>

For beginners:

• staff tells us which staff this is
• layer tells us which musical stream or voice on that staff

Key signatures are generally defined at the score or staff level, often through:

• <scoreDef>
• <staffDef>
• the keysig attribute

Example:

<scoreDef keysig="1s"/>

A beginner reading of this is:

• keysig stores the written key signature
• 1s means one sharp

Similarly:

<scoreDef keysig="2f"/>

means two flats.

For beginners it is enough to understand that:

• the key signature is usually a context-setting property
• it applies to the following music until changed

Meter is also typically defined in scoreDef or staffDef.

The most common beginner attributes are:

• meter.count = top number
• meter.unit = bottom number

Example:

<scoreDef meter.count="4" meter.unit="4"/>

This means 4/4.

Another example:

<scoreDef meter.count="3" meter.unit="8"/>

This means 3/8.

Clefs are usually part of the score or staff definition as well.

Typical attributes are:

• clef.shape
• clef.line

Example:

<staffDef n="1" clef.shape="G" clef.line="2"/>

This gives a treble clef on line 2.

One of the most important attributes in MEI is:

xml:id

This gives an element a unique identifier inside the document.

Example:

<note pname="g" oct="4" dur="4" xml:id="n42"/>

The key idea is:

xml:id gives this exact note its own identity.

That matters because other elements can refer to it.

For beginners, xml:id does three important things:

• it makes an element uniquely identifiable
• it allows linking
• it helps keep references stable

This is especially useful when we want to say:

• a dynamic starts at this note
• a slur begins here and ends there
• this annotation belongs to that symbol
• this facsimile zone corresponds to this note

<measure n="10">
  <staff n="1">
    <layer n="1">
      <note pname="f" oct="4" dur="4"/>
      <note pname="g" oct="4" dur="4" xml:id="n10_2"/>
      <note pname="a" oct="4" dur="4"/>
      <note pname="c" oct="5" dur="4"/>
    </layer>
  </staff>
 
  <dynam startid="#n10_2">f</dynam>
</measure>

Here:

• the second note has xml:id=„n10_2“
• the dynamic uses startid=„#n10_2“
• the # means „point to the element with this id“

So the dynamic is explicitly attached to that note.

For editorial and analytical work, xml:id is crucial because it lets us refer to specific musical objects.

That is important when:

• encoding slurs, ties, dynamics, and other control elements
• linking notation to facsimile zones
• attaching annotations
• documenting editorial intervention
• aligning musical data across tools

In practical terms:

• the note is no longer just „the third note in bar 10“
• it becomes a uniquely addressable object

A good beginner analogy is:

• the element itself is the musical object
• xml:id is its name tag
• another element can point to that name tag

Without xml:id, references are harder. With xml:id, you can point exactly to one specific note or symbol.

Not always.

In principle, a note can be encoded without xml:id.

Example:

<note pname="c" oct="4" dur="4"/>

But as soon as you want to point to that note from elsewhere, a unique identifier becomes extremely useful, and often necessary in practice.

For editorial workflows, it is often a very good idea to assign stable xml:id values systematically.

• MEI is an XML language for music notation
• XML consists of elements and attributes
• a schema is the rulebook for valid XML
• notes in MEI are often defined by pname, oct, and dur
• measures group the music into bars
• scoreDef and staffDef define context such as clef, key, and meter
• xml:id gives a specific element a unique identity
• other elements can point to that identity using attributes like startid and endid

<score>
  <scoreDef keysig="1s" meter.count="4" meter.unit="4"/>
  <section>
    <measure n="1">
      <staff n="1">
        <layer n="1">
          <note pname="g" oct="4" dur="4" xml:id="m1n1"/>
          <note pname="a" oct="4" dur="4" accid="s" xml:id="m1n2"/>
          <note pname="b" oct="4" dur="4" xml:id="m1n3"/>
          <note pname="c" oct="5" dur="4" xml:id="m1n4"/>
        </layer>
      </staff>
      <dynam startid="#m1n2">f</dynam>
    </measure>
  </section>
</score>

This example shows:

• a score definition with key and meter
• one measure
• one staff
• one layer
• notes with pitch, octave, and duration
• one accidental
• unique xml:id values
• a dynamic linked to a specific note

For the official reference documentation, see:

• MEI Guidelines: Introduction