Lab: XMLTree Model


Objectives

Even though this lab does not involve any programming, it does have an important and fundamental objective, that is, to ensure you understand completely what the value of an XMLTree object looks like. Please make sure you answer each of the questions in this lab carefully and thoughtfully. Discuss them with the classmate sitting next to you and write down all the answers so that an instructor can check them out. If you encounter any problems or you have any doubts about any of the questions, please make sure you ask an instructor for help.

The Problem

The XMLTree family of components provides convenient functionality to read and process XML documents. Understanding the model of an XMLTree is essential to being able to use these components. This lab activity will take you step-by-step through the concepts needed to understand the model. In the next lab you will learn and practice how to manipulate XMLTrees with the methods provided by the XMLTree component.

Method

Carefully consider and answer the questions below.

What's a Tree?

Given the tree of colors below, answer the following questions.

  1. What's the root of the tree?
  2. What are the leaves of the tree?
  3. What are the children of the node blue?
  4. What is the parent of the node cyan?
  5. What nodes are on the path from the root to the node orange?
  6. What is the size of the tree?
  7. What is the height of the tree?

What's XML?

Consider the following XML document and answer the questions below.

<WebServiceResponse>
 <status>OK</status>
 <result>
  <type>Building</type>
  <name>Dreese Labs</name>
  <location>
   <lat>40.002382</lat>
   <lng>-83.015958</lng>
  </location>
 </result>
 <result>
  <message>CSE Department</message>
 </result>
</WebServiceResponse>

  1. What are the tags in this XML document?
  2. What are the text strings in this XML document?
  3. What are the attributes for each tag in this XML document?
  4. Draw a tree that captures the structure (nesting) of this XML document.

Now consider the following XML document and answer the questions below.

<album label="Sony">
  <title>Gershwin: Rhapsody In Blue / An American In Paris</title>
  <composer>George Gershwin</composer>
  <conductor>Leonard Bernstein</conductor>
  <released date="Oct 25, 1990"></released>
  <tracks>
    <track number="1" duration="16:29">Rhapsody in Blue</track>
    <track number="2" duration="18:30">An American in Paris</track>
  </tracks>
</album>

  1. What tags have attributes?
  2. For each tag with attributes, list the attribute name and the corresponding attribute value.

What's an XMLTree?

Here is a picture of an XMLTree representing the second XML document above.

  1. Match each node in the tree with a line in the XML document above (draw a tree with the same layout as the given XMLTree where each node has the line number corresponding to that node).
  2. Draw the node(s) in the tree that correspond to line 3 in the XML document.
  3. Draw the node(s) in the tree that correspond to line 8 in the XML document.
  4. What line(s) in the XML document correspond to the <conductor> node?
  5. What line(s) in the XML document correspond to the <tracks> node?
  6. What's the only tag node that is a leaf in the XMLTree?

Paths in XMLTree

Recall that in an XMLTree the children of a given node are numbered with increasing integer values (indices, positions) starting at 0 for the first child, 1 for the second child, etc. For instance, in the XMLTree above, <title> is child 0 of <album>, <composer> is child 1, <conductor> is child 2, and so on.

  1. What is child 3 of <album>?
  2. What is child 0 of <tracks>?
  3. What is child 1 of <composer>?

A path in an XMLTree can be identified in two different ways by either listing the labels of the nodes on the path or by listing the index of each node (except the root) as a child of its parent. So, for instance, a path from the root to the George Gershwin node can be identified either by listing the nodes on the path: (<album>, <composer>, George Gershwin), or by listing the root followed by the indices corresponding to the nodes on the path: (<album>, 1, 0) because <composer> is child 1 of <album> and George Gershwin is child 0 of <composer>.

Consider the text node An American in Paris in the XML tree above.

  1. Draw the nodes on a path from the root of the tree to this node.
  2. For each of the nodes on this path (except for the root), what is the integer index of the node as a child of its parent?

Adding Attributes

Suppose we modified the XML document above so that both the <composer> and the <conductor> tags have an attribute born whose value is the date of birth, i.e.,

  <composer born="Sep 26, 1898">George Gershwin</composer>
  <conductor born="Aug 25, 1918">Leonard Bernstein</conductor>

  1. Draw the nodes in the XMLTree that would have to be modified to include this new information.

Replacing Attribute with Child

Now suppose we wanted to change the <released> tag in the XML document above so that the date is not an attribute of the tag but instead a text child of the tag node.

  1. Rewrite line 5 in the XML document above to show the result of this change.
  2. Draw the nodes in the XMLTree that would have to be modified to reflect this change in the XML document.

Drawing an XMLTree

Consider the following XML document:

<weather>
  <location>
    <city>Columbus</city>
    <state>OH</state>
  </location>
  <current text="Light Rain" high="75" low="54" date="8 Sep 2012"></current>
  <forecast text="Sunny" high="79" low="52" date="9 Sep 2012"></forecast>
</weather>

  1. Draw the complete XMLTree corresponding to this document.
  2. A city is logically inside a state. So, change the structure of the XML document to put the <city> element inside the <state> element. What essentially arbitrary decision did you make when doing this? Redraw the part of the XMLTree that is changed by this modification, taking care to match the document with respect to the decision just mentioned.

Let's Explore!

For this part of the lab, you will use a program that allows the user to load XML documents into XMLTree objects and display their values. You can run this program by importing it into Eclipse. First you need to download the project archive, xmltree-viewer.zip, to your computer. Click on this download link and save the file somewhere on your hard drive where you can easily find it. Make sure that you do not expand this archive. If your browser automatically expands downloaded zip archives, that's OK too. Just pay attention to the special instructions in the following few steps. You may want to make a note of where you saved it.

Import your new project in Eclipse by following these steps:

  1. From the File menu select Import....
  2. In the new window, expand General and select Existing Projects into Workspace. Click Next.
  3. Click on the radio button next to Select archive file and then click the Browse... button. (If the archive was expanded when you downloaded the file to your own computer, click on Select root directory... instead.)
  4. In the file selection window, find the xmltree-viewer.zip file and select it. (If your browser expanded the archive, find the xmltree-viewer directory instead.) Click OK.
  5. Click Finish.

To run the program, find the RunViewer.java file in the src folder in the project and run it as usual as a Java Application.

Once you start the program, you can enter the URL of an XML document or a path on the local drive for an XML file in the XML Input field and click Go to load an XML document, open a new window, and display the value of the corresponding XMLTree. There are several ways to enter your input in the field: you can type the URL or file path, or you can use the Browse... button to locate a file on the local drive, or you can select one of the entries you have used before (if any) in the drop-down menu.

Copy and paste (or type) the entry http://web.cse.ohio-state.edu/software/2221/web-sw1/extras/instructions/xmltree-model/album.xml in the address bar and click Go. This XML document contains the XML example we used earlier. Expand all the nodes and see how the tree displayed in the viewer window matches with the XMLTree picture above.

In particular, observe the different icons used to identify tags and text nodes; also note how attributes and their values are displayed between []. Make sure you do not continue until you can match each element in the XMLTree above to each element of the XMLTree displayed in the viewer.

Now let's open a page downloaded from Yahoo's weather forecast XML service. Copy and paste (or type) the entry http://web.cse.ohio-state.edu/software/2221/web-sw1/extras/instructions/xmltree-model/columbus-weather.xml in the address bar and click Go.

Answer the following questions by exploring the XMLTree displayed.

  1. What is the root node?
  2. How many attributes does the root tag have?
  3. What is the value of the yahoo:lang attribute of the root tag?
  4. How many children does the root node have?
  5. How many children does the <results> node have?
  6. How many children does the <channel> node have?
  7. What is the range of indices of the children of the <channel> node?
  8. What is the index of the <yweather:location> child of the <channel> node?
  9. What are the names and values of the attributes of the <yweather:location> tag?
  10. Under the <item> child of the <channel> node, find the <geo:lat> and <geo:long> tags. What are the latitude and longitude of your chosen location?
  11. For both the latitude and longitude text nodes give the list of indices of the path from the root to the corresponding text node.
  12. Under the <item> child of the <channel> node, find the node with the forecast for January 31 2017. What is the label of this node?
  13. What is the index of this node as a child of the <item> node?
  14. What are the names and values of the attributes of this node (i.e., what is the weather forecast for that day)?
  15. What is the height of the tree?
  16. List the nodes on a longest path from the root to a leaf (i.e., a path of length equal to the height of the tree).
  17. For each of the nodes on this path (except for the root), what is the integer index of the node as a child of its parent?

Additional Activities

  1. Use the XMLTreeViewer program to explore other XML documents (e.g., from your favorite RSS feeds) to get a better understanding of XML and the XMLTree model.