DOM is a standard API for parsing XML developed by the W3C. Qt provides a non-validating DOM Level 2 implementation for reading, manipulating, and writing XML documents.
DOM represents an XML file as a tree in memory. We can navigate through the DOM tree as much as we want, and we can modify the tree and save it back to disk as an XML file.
Let's consider the following XML document:
<quote>Scio me nihil scire</quote>
<translation>I know that I know nothing</translation>
It corresponds to the following DOM tree:
The DOM tree contains nodes of different types. For example, an
Element
node corresponds to an opening tag and its matching closing tag. The material that falls between the tags appears as child nodes of the
Element
node. In Qt, the node types (like all other DOM-related classes) have a
QDom
prefix; thus,
QDomElement
represents an
Element
node, and
QDomText
represents a
Text
node.
Different types of nodes can have different kinds of child nodes. For example, an
Element
node can contain other
Element
nodes, as well as
EntityReference
,
Text
,
CDATASection
,
ProcessingInstruction
, and
Comment
nodes.
Figure 16.3
shows which nodes can have which kinds of child nodes. The nodes shown in gray cannot have any child nodes of their own.
To illustrate how to use DOM for reading XML files, we will write a parser for the book index file format described in the preceding section.
In readFile(), we begin by trying to open the file whose name was passed in. If an error occurs, we output an error message and return false to signify failure. Otherwise, we set up some variables to hold parse error information, should they be needed, and then create a QDomDocument. When we call setContent() on the DOM document, the entire XML document provided by the QIODevice is read and parsed. The setContent() function automatically opens the device if it isn't already open. The false argument to setContent() disables namespace processing; refer to the QtXml reference documentation for an introduction to XML namespaces and how to handle them in Qt.
If an error occurs, we output an error message and return false to indicate failure. If the parse is successful, we call documentElement() on the QDomDocument to obtain its single QDomElement child, and we check that it is a <bookindex> element. If we have a <bookindex>, we call parseBookindexElement() to parse it. As in the preceding section, the parsing is done using recursive descent.
void DomParser::parseBookindexElement(const QDomElement &element)
QDomNode child = element.firstChild();
while (!child.isNull()) {
if (child.toElement().tagName() == "entry")
parseEntryElement(child.toElement(),
treeWidget->invisibleRootItem());
child = child.nextSibling();
In parseBookindexElement(), we iterate over all the child nodes. We expect each node to be an <entry> element, and for each one that is, we call parseEntry() to parse it. We ignore unknown nodes, to allow for the book index format to be extended in the future without preventing old parsers from working. All <entry> nodes that are direct children of the <bookindex> node are top-level nodes in the tree widget we are populating to reflect the DOM tree, so when we want to parse each one we pass both the node element and the tree's invisible root item to be the widget tree item's parent.
The QDomNode class can store any type of node. If we want to process a node further, we must first convert it to the right data type. In this example, we only care about Element nodes, so we call toElement() on the QDomNode to convert it to a QDomElement and then call tagName() to retrieve the element's tag name. If the node is not of type Element, the toElement() function returns a null QDomElement object, with an empty tag name.
void DomParser::parseEntryElement(const QDomElement &element,
QTreeWidgetItem *parent)
QTreeWidgetItem *item = new QTreeWidgetItem(parent);
item->setText(0, element.attribute("term"));
QDomNode child = element.firstChild();
while (!child.isNull()) {
if (child.toElement().tagName() == "entry") {
parseEntryElement(child.toElement(), item);
} else if (child.toElement().tagName() == "page") {
parsePageElement(child.toElement(), item);
child = child.nextSibling();
In parseEntryElement(), we create a tree widget item. The parent item that is passed in is either the tree's invisible root item (if this is a top-level entry) or another entry (if this is a sub-entry). We call setText() to set the text shown in the item's first column to the value of the <entry> tag's term attribute.
Once we have initialized the QTreeWidgetItem, we iterate over the child nodes of the QDomElement node corresponding to the current <entry> tag. For each child element that is an <entry> tag, we call parseEntryElement() recursively with the current item as the second argument. Each child's QTreeWidgetItem will then be created with the current entry as its parent. If the child element is a <page>, we call parsePageElement().
In parsePageElement(), we call text() on the element to obtain the text that occurs between the <page> and </page> tags; then we add the text to the comma-separated list of page numbers in the QTreeWidgetItem's second column. The QDomElement::text() function navigates through the element's child nodes and concatenates all the text stored in Text and CDATA nodes.
Let's now see how we can use the DomParser class to parse a file:
int main(int argc, char *argv[])
QApplication app(argc, argv);
QStringList args = QApplication::arguments();
QTreeWidget treeWidget;
DomParser parser(&treeWidget);
for (int i = 1; i < args.count(); ++i)
parser.readFile(args[i]);
return app.exec();
We start by setting up a QTreeWidget. Then we create a DomParser. For each file listed on the command line, we call DomParser::readFile() to open and parse each file and populate the tree widget.
Like the previous example, we need the following line in the application's .pro file to link against the QtXml library:
QT += xml
As the example illustrates, navigating through a DOM tree is straightforward, although not quite as convenient as using QXmlStreamReader. Programmers who use DOM a lot often write their own higher-level wrapper functions to simplify commonly needed operations.
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 [email protected].
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 [email protected] 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 [email protected].
Supplemental Privacy Statement for California Residents
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.
){kind=link}