Publication: XML Journal
Publication Date: 01-JAN-04
Format: Online - approximately 2047 words
Delivery: Immediate Online Access
Author: Burton, Philip ; Bruhn, Russel
Article Excerpt
XML is the appropriate format for semistructured data, that is, data with a natural tree structure. Trees are a special form of graphs, and a dialect of XML called GraphML now exists that provides a standard set of tags for describing them. To visualize or draw the graph we can use another XML dialect called SVG, or Scalable Vector Graphics.
SVG is a language for describing two-dimensional graphics and graphical applications and is a dialect of XML. In this article we discuss the representation of tree-structured data using XML and GraphML. We visualize the data using SVG and transform the data between the various XML documents using Extensible Stylesheet Language Transformations (XSLT).
Introduction
A graph is simply a collection of nodes and edges and may be directed or undirected. In the case of a directed graph, an arrow connects the source to the target; for an undirected graph there is no arrow, only a line. A tree is a special case of a graph: there are no closed loops or circuits but all the nodes are connected. XML documents satisfy this definition and thus exhibit a natural tree structure. Examples of trees include decision trees, concept maps, and the structure of hydrocarbon molecules.
The structure of a tree is shown in Figure 1. The rectangles are the nodes and the edges are the lines connecting the nodes. Node A is a source and targets nodes B, C, and D; similarly, source node D targets nodes E and E
[FIGURE 1 OMITTED]
The tree in Figure 1 can be represent ed in XML by a series of tags as shown in Figure 2. The nodes of the tree become tags in XML.
[FIGURE 2 OMITTED]
Alternatively, we can use a standard format like GraphML to illustrate a tree. In GraphML the tree shown in Figure 1 becomes the listing in Figure 3.
Figure 3 * GraphML
The "graph" element is the mot...
NOTE: All illustrations and photos have been removed from this article.
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