Writing Our Own ML without a Net: Examples

So now we're going to create our own markup language (ML) that will be used throughout the rest of this article (both parts). We could start by creating a DTD, but the DTD syntax is complicated and not the way some of us naturally think about markup. Trust me -- we don't need the (DTD) net, at least not yet.

Some of you may recall my fondness for the Beatles from my first \ XML article. Let's create an XML description of a tiny fraction of my Beatles collection. In fact, we'll call this Collection Markup Language, or Collection ML for short. Why not Beatles ML? Because it will have general elements that are not at all explicitly associated with the Beatles. Why not Record ML? Because the collection may contain CDs, record albums (for those of us old enough to remember vinyl), books, and so forth. (Like most small XML examples, the language will be a bit contrived, meant more for illustrative purposes than to be useful in and of itself.)

Examples XML documents, DTD, and images	Several small XML documents needed to follow the remainder of this article. Install them anywhere you wish, but subsequent downloads should be in the same location (folder).
Examples/doingit1.zip (approx. 54 KB)	Requires Zip. Depending on your browser, you'll probably want to do a Save As (Download). If you don't have zip utilities, download each file separately.
Zip Contents: Explanation: Examples/collection1.xml correct XML document without DTD reference Examples/collection1.dtd correct DTD which describes Collection ML Examples/collection1bugs.xml contains several XML syntax bugs for you to find Examples/collection1dtd.xml references local (SYSTEM) DTD by relative path Examples/collection1pubdtd.xml references public (PUBLIC) DTD by URL Examples/collection1bugsdtd.xml references a DTD containing a DTD syntax error Examples/collection1bugs.dtd DTD with a syntax error Examples/collection1pubbugs.xml invalid document with respect to public DTD Examples/collection1xml.gif GIF showing how IE5 displays XML (default) Examples/mathML.gif GIF showing how Amaya displays MathML Examples/mathML1.xml a simple MathML document Examples/mathML2.xml another simple MathML document

After you unzip or download the files, take a close look at Examples/collection1.xml. (With some browsers, you may needed to use a text editor to view the XML file, reproduced below for your convenience.)

A Collection consists of Book and CD elements in no particular order. I'd like to be able to enter the information and deal with the presentation and ordering later (in part 2 of this article). Most of the elements in Collection ML have few if any attributes. There's no particular reason for this limitation other than to keep the example relatively simple. In fact, where I used attributes as opposed to elements may seem a bit arbitrary; this will be covered in the section To E or Not To E: Elements vs. Attributes. Also, except for Collection, Book, CD, and Chart, the elements are not very hierarchical; only a few elements can contain other elements. However, this is arguably a reasonable way to express the Book and CD information, so we won't be too harsh on the language creator. (The Owner element and owner attribute of Collection refer to the same thing, so one is redundant.) The Book element has optional nested elements Notes and Rating. The Label element has an optional attribute called country. Peak has optional elements weeks and country.

<?xml version="1.0" standalone="yes" ?>

<!-- A Collection consists of Book and CD elements 
in no particular order. -->

<Collection owner="Ken Sall" location="nevermind">
  <Owner>Ken Sall</Owner>
  <Book>
  <Title>Complete Beatles Chronicle, The</Title>
  <Author>Lewisohn, Mark</Author>
  <Type>Chronology</Type>
  <Published publisher="Harmony Books">
  1992</Published>
  <Rating>5 stars</Rating>
  <Notes>
  Covers the years 1957 through 1970. No solo info.
  Great appendices with chart info, discography, 
  composer index,radio, tv, and live performances, 
  and much more.
  </Notes>
  </Book>
  <CD>
  <Title>Band on the Run</Title>
  <Artist>McCartney, Paul and Wings</Artist>
  <Chart>
    <Peak weeks="4">1</Peak>
    <Peak country="UK">1</Peak> <!-- guess -->
  </Chart>
  <Type>Rock</Type>
  <Label>Capitol</Label>
  <Label country="UK">EMI</Label>
  <AlbumReleased>1973</AlbumReleased>
  <Remastered format="gold CD">1993</Remastered>
  <Remastered format="2 disc box set with booklet">
  1999</Remastered>
  </CD>
  <CD>
  <Title>Venus and Mars</Title>
  <Artist>McCartney, Paul and Wings</Artist>
  <Chart>
    <Peak weeks="1">1</Peak>
    <Peak country="UK">2</Peak> <!-- guess -->
  </Chart>
  <Type>Rock</Type>
  <Label>Capitol</Label>
  <Label country="UK">EMI</Label>
  <AlbumReleased>1975</AlbumReleased>
  <Remastered format="gold CD with 3 bonus tracks">
  1994</Remastered>
  </CD>
  <Book>
  <Title>Many Years From Now</Title>
  <Author>McCartney, Paul</Author>
  <Type>Autobiographical</Type>
  <Published publisher="Henry Holt and Company">
  1997</Published>
  <!-- Notice the absence of Notes and 
  Rating elements. I haven't read this book yet. 
  This illustrates some optional elements that 
  are children of Book element.
  -->
  </Book>
</Collection>

What's It All About, Ælfred?
Doing It With XML, Part 1
To E or Not To E: Elements vs. Attributes