Converting XML to DOT

Question

I would like to show an XML tree as a tree using GraphViz Dot tool. Then I must convert it to a DOT file.

It is what I have tried

 string dot = "digraph G {" + Environment.NewLine;
 XML2DOT(XmlRoot, "r");
 dot += Environment.NewLine + "}";
 ....
 private void XML2DOT(XmlNode n, string id)
 {
 if (n == null)
 return;
 string NodeName = n.Name.Replace("-", "_");
 if (n.HasChildNodes)
 {
 dot += Environment.NewLine + NodeName 
 + id + "[label=\"" + NodeName + "\"];";
 }
 else
 {
 dot += Environment.NewLine 
 + "leaf" + id + "[label=\"" + n.InnerText + "\"];";
 }
 int i = 0;
 foreach (XmlNode item in n.ChildNodes)
 {
 string cid = id + i;
 dot += Environment.NewLine + NodeName + id + " -> " 
 + (item.HasChildNodes ? item.Name.Replace("-", "_") : "leaf") 
 + cid + ";";
 XML2DOT(item, cid);
 i++;
 }
 }

The input xml is:

<?xml version="1.0" encoding="UTF-8"?>
<S>
<MN clitic="empty" ne_sort="pers">
 <PUNC clitic="empty">
 <w clitic="empty" gc="Ox" lc="Ox" lemma="#">#</w>
 </PUNC>
 <MN clitic="empty" ne_sort="pers">
 <N clitic="ezafe">
 <w clitic="ezafe" gc="Apsz ; Nasp--- ; Nasp--z ; Ncsp--z" lc="Nasp--z" lemma="مسعود" n_type="prop" ne_sort="pers">مسعود</w>
 </N>
 <N clitic="ezafe">
 <w clitic="ezafe" gc="Apsy ; Nasp--- ; Nasp--z ; Ncsp--y" lc="Nasp--z" lemma="شجاعی" n_type="prop" ne_sort="pers">شجاعی</w>
 </N>
 <N clitic="empty">
 <w clitic="empty" gc="Nasp--- ; Nasp--z" lc="Nasp---" lemma="طباطبایی" n_type="prop" ne_sort="pers">طباطبایی</w>
 </N>
 </MN>
 <PUNC clitic="empty">
 <w clitic="empty" gc="Ox" lc="Ox" lemma="#">#</w>
 </PUNC>
</MN>
</S>

And it is what I get:

enter image description here

It works as expected, just would like to know a more general and efficient way to do that.

Answer 1

There's an XML syntax for DOT called DotML at http://martin-loetzsch.de/DOTML/. Generating a generic DotML tree from XML is very straightforward using XSLT. Most of it is just:

<xsl:template match="*">
 <node id="{generate-id()}" label="{name()}"/>
 <edge from="{generate-id(..)}" to="{generate-id()}"/>
 <xsl:apply-templates/>
</xsl:template>
<xsl:template match="text()">
 <node id="{generate-id()}" label="{.}"/>
 <edge from="{generate-id(..)}" to="{generate-id()}"/>
</xsl:template>

Answer 2

You should not concatenate strings like this, it's inefficient. Instead, use a StringBuilder.

---

I'm unclear on how is the method supposed to be used. In the usage, it looks like dot is a local variable, while in the method itself, it looks like it's a field. If you want to stick with string, return it from the method. If you're going to switch to StringBuilder, accept it as a parameter.

Also, the whole process, including digraph, should be encapsulated into a method.

---

The scheme you're using for producing unique node IDs does not actually produce IDs that are unique. For example r + 1 + 0 produces the same ID as r + 10.

A simple solution would be to have a single i for the whole conversion.

---

You have some small pieced of code that repeat. Especially if you can use C# 6.0 expression bodied methods, I would extract them into separate methods.

---

Your code does not handle XML elements with no content (e.g. <elem />) well: it presents them as empty text nodes.

---

What does cid mean? Child ID? Don't abbreviate names unnecessarily.

---

The common convention in C# is to use camelCase for local variables, you mostly follow that, except for NodeName, which should be nodeName.

Also, 3-letter abbreviations are almost always not fully capitalized (e.g. it's XmlNode, not XMLNode), you should follow that convention too: Xml2Dot instead of XML2DOT.

And XML2DOT is not a great method name either. Method names should usually be verbs.

---

The final result could look like this:

class XmlToDotConverter
{
 private const string Leaf = "leaf";
 private readonly StringBuilder stringBuilder = new StringBuilder();
 private int i;
 public string Convert(XmlDocument document)
 {
 stringBuilder.Clear();
 stringBuilder.AppendLine("digraph G {");
 ConvertNode(document.DocumentElement, i);
 stringBuilder.Append('}');
 return stringBuilder.ToString();
 }
 private static string ConvertName(XmlNode node)
 => node.Name.StartsWith("#") ? Leaf : node.Name.Replace("-", "_");
 private void AppendNode(string name, int id, string text)
 {
 stringBuilder.AppendLine($"{name}{id}[label=\"{text}\"];");
 // or the following, if you care about performance more than about readability
 //stringBuilder
 // .Append(name)
 // .Append(id)
 // .Append("[label=\"")
 // .Append(text)
 // .Append("\"];")
 // .AppendLine();
 }
 private void AppendEdge(string fromName, int fromId, string toName, int toId)
 => stringBuilder.AppendLine($"{fromName}{fromId} -> {toName}{toId};");
 private void ConvertNode(XmlNode node, int id)
 {
 if (node.NodeType == XmlNodeType.Element)
 {
 string nodeName = ConvertName(node);
 AppendNode(nodeName, id, nodeName);
 foreach (XmlNode childNode in node.ChildNodes)
 {
 i++;
 int childId = i;
 AppendEdge(nodeName, id, ConvertName(childNode), childId);
 ConvertNode(childNode, childId);
 }
 }
 else if (node.NodeType == XmlNodeType.Text)
 {
 AppendNode(Leaf, id, node.InnerText);
 }
 }
}