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POStoring Relational Data in XML
 

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    <p>I'm wondering what the best practices are for storing a relational data structure in XML. Particulary, I am wondering about best practices for enforcing node order. For example, say I have three objects: <code>School</code>, <code>Course</code>, and <code>Student</code>, which are defined as follows:</p> <pre><code>class School { List&lt;Course&gt; Courses; List&lt;Student&gt; Students; } class Course { string Number; string Description; } class Student { string Name; List&lt;Course&gt; EnrolledIn; } </code></pre> <p>I would store such a data structure in XML like so:</p> <pre><code>&lt;School&gt; &lt;Courses&gt; &lt;Course Number="ENGL 101" Description="English I" /&gt; &lt;Course Number="CHEM 102" Description="General Inorganic Chemistry" /&gt; &lt;Course Number="MATH 103" Description="Trigonometry" /&gt; &lt;/Courses&gt; &lt;Students&gt; &lt;Student Name="Jack"&gt; &lt;EnrolledIn&gt; &lt;Course Number="CHEM 102" /&gt; &lt;Course Number="MATH 103" /&gt; &lt;/EnrolledIn&gt; &lt;/Student&gt; &lt;Student Name="Jill"&gt; &lt;EnrolledIn&gt; &lt;Course Number="ENGL 101" /&gt; &lt;Course Number="MATH 103" /&gt; &lt;/EnrolledIn&gt; &lt;/Student&gt; &lt;/Students&gt; &lt;/School&gt; </code></pre> <p>With the XML ordered this way, I can parse <code>Courses</code> first. Then, when I parse <code>Students</code>, I can look up each <code>Course</code> listed in <code>EnrolledIn</code> (by its <code>Number</code>) in the <code>School.Courses</code> list. This will give me an object reference to add to the <code>EnrolledIn</code> list in <code>Student</code>. If <code>Students</code>, however, comes <em>before</em> <code>Courses</code>, such a lookup to get a object reference is not possible. (Since <code>School.Courses</code> has not yet been populated.)</p> <p>So what are the best practices for storing relational data in XML? - Should I enforce that <code>Courses</code> must always come before <code>Students</code>? - Should I tolerate any ordering and create a stub <code>Course</code> object whenever I encounter one I have not yet seen? (To be expanded when the definition of the <code>Course</code> is eventually reached later.) - Is there some other way I should be persisting/loading my objects to/from XML? (I am currently implementing <code>Save</code> and <code>Load</code> methods on all my business objects and doing all this manually using <code>System.Xml.XmlDocument</code> and its associated classes.)</p> <p>I am used to working with relational data out of SQL, but this is my first experience trying to store a non-trivial relational data structure in XML. Any advice you can provide as to how I should proceed would be greatly appreciated.</p>
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    1. USJoseph Sturtevant
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