Home > Articles > Web Services > XML

  • Print
  • + Share This
Like this article? We recommend

Parsing the XML

Before you can do anything with the XML data, you need some way to parse it into the tree. Parsing is actually a two-step process:

  1. Locate the elements that you want to parse. An XML document can contain comments and processing instructions. In addition, you might not want to start with the root node (Categories, in this case).

  2. Now that you have a starting place, look through the various elements—at least until you've reached the depth within the document that you want. The example relies on recursion to perform this task, and it keeps parsing until the entire document is completed.

Starting the Parsing Process

The sample application makes an assumption about the XML document—it relies on Categories being the root node. (You could easily modify this assumption to consider other document types.) Listing 2 shows how the example starts the parsing process by looking for the Categories node.

Listing 2 Starting the Parsing Process

private void mnuFileParse_Click(object sender, System.EventArgs e)
{
  XmlDocument Doc; // Holds the XML data.
  XmlNodeList Cats; // All of the categories.

  // Load the XML document.
  Doc = new XmlDocument();
  Doc.Load("CategoryList.XML");

  // Get the list of categories.
  Cats = Doc["Categories"].ChildNodes;

  // Parse the list.
  CheckChildren(Cats, null);
}

NOTE

The example leaves out error trapping for the sake of clarity.

The code begins by loading an XML document that resides on the local hard drive, but the example doesn't really care where the XML document resides. You could easily download the XML data from a web site or even get it as part of a web service call. To use this technique, however, you must have full access to the XML document and not just an XML fragment. In addition, the document must be well-formed or the Common Language Runtime (CLR) will throw an error.

After the document loads, the code obtains the child nodes of the Categories root node. Leaving out the root node reduces the processing time and possible problems, but you could easily process the root node as well. Finally, the code sends these nodes to CheckChildren(), described in the next section.

Using Recursion for Parsing

Recursion can be a wonderful technique for working with documents of unknown configuration, because you don't have to track individual levels—the code does it for you automatically. The problem with recursion is that it substantially increases the memory requirements for an application. There's always the chance of running out of memory. However, you really won't run into a problem with most modern machines—the dataset would have to be immense to run out of memory (at which point, you should consider other parsing techniques). Listing 3 shows how this example uses recursion for parsing.

Listing 3 Using Recursion To Parse the XML Document

private void CheckChildren(XmlNodeList List, TreeNode ParentNode)
{
  Int32  NewNode;  // Number of a new node.

  // Look at each node.
  foreach (XmlNode ThisNode in List)
  {
   // Determine whether this is a text (value) node.
   if (ThisNode.NodeType == XmlNodeType.Text)
   {
     // Add the value to the parent's tag value.
     ParentNode.Tag = ThisNode.Value;

     // Return without further processing.
     return;
   }

   // Determine whether this is a top-level node.
   if (ThisNode.Attributes["Parent"].Value == "0")
   {

     // Add the node to the top of the tree.
     NewNode = tvNodes.Nodes.Add(new TreeNode(ThisNode.Name, 0, 1));

     // Determine if this is the end of this level.
     if (ThisNode.ChildNodes.Count == 0)

      // Return nothing.
      return;

     else
      // Otherwise, there is something to process.
      CheckChildren(ThisNode.ChildNodes, tvNodes.Nodes[NewNode]);
   }
   else
   {
     // Determine whether this is the end of this level.
     if (ThisNode.ChildNodes.Count == 0)
     {

      // Add a subordinate leaf node.
      NewNode = ParentNode.Nodes.Add(new TreeNode(ThisNode.Name, 2, 3));

      // Return nothing.
      return;
     }

     else
     {
      // Add a subordinate parent node.
      NewNode = ParentNode.Nodes.Add(new TreeNode(ThisNode.Name, 0, 1));

      // Process the next child.
      CheckChildren(ThisNode.ChildNodes, ParentNode.Nodes[NewNode]);
     }
   }
  }
}

The code begins by taking a shortcut—it uses a foreach statement to select each node in turn for processing. The code continues processing until all of the nodes at a certain level are processed. It's a little hard to wrap your brain around recursion sometimes, but CLR keeps each level separate through use of the stack.

Every call to CheckChildren() begins a new level of processing. Some levels are text nodes that contain the value for a particular element. The code checks for text nodes next and saves this value in the parent node's Tag property. When an element doesn't have a value associated with it, the Tag property remains null. Consequently, it's easy to determine when an element is a leaf node.

The top-level nodes require special processing. Perhaps you want to assign a special icon to the top-level nodes, or simply want to reduce the amount of processing time because you know that the top-level nodes always have children. However, the top-level nodes also require special processing for another reason—they form the nodes to which all other nodes attach in the tree view. Consequently, these nodes don't have any parent nodes, and you must handle them differently.

The code begins by adding the node to the TreeView control, tvNodes. Notice that the code relies on the Add() method and creates a new TreeNode control to fill it. You'll need to create an ImageList control and assign it to the tvNodes' ImageList property to add icons to the various layers. The example uses four icons: parent node closed, parent node open, leaf node closed, and leaf node open. When the top-level node has one or more children, the code calls CheckChildren() recursively. Otherwise, it ends processing for the current node and moves on to the next node.

Nodes that appear at the second level or greater might not have any children. When a child node doesn't have children, the code adds the child node to the list by using the leaf node icons. Notice also that the code adds the node to the parent, not to tvNodes. This technique ensures that you don't have to track which level the code is at because you never work directly with tvNodes unless you're adding a top-level node.

A child node with children receives the parent node icons. Note that CLR treats a child node with a value as a node that has children—the only difference is that the child is a text node, not an element. Consequently, when you want the code to use a leaf node icon for all children that don't have other elements as children, you need to peek at the next level to see what kind of children the node contains. As with a parent node, the code makes a recursive call to CheckChildren() to continue processing the node levels.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020