Home > Articles > Web Services > XML

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


Listing 3 shows the XSLT used to generate the HTML in Listing 2. Because XSLT is an XML vocabulary, its structure should be familiar to you. As you examine it, notice that the element names fall into two categories—those that begin with the prefix xsl: and those that don’t. The elements that begin with xsl: are part of the XSLT vocabulary; all the other elements are HTML (<html>, <body>, <head>, <h1>, and so on).


For our parser to distinguish between different vocabularies, we need to understand namespaces. XML namespaces is an official W3C recommendation that uses Uniform Resource Identifiers (URIs) as the basis for distinguishing different XML vocabularies. URIs are a set of character strings, defined by a generic URI syntax, used for identifying resources.

Since URIs are difficult to write and may contain characters that violate XML element-naming rules, XML namespaces permits the use of shorthand prefixes to stand in for a URI. Thus, while the official XSLT namespace is http://www.w3.org/1999/XSL/Transform, common practice is to use the prefix xsl:. In our XSLT example, lines 2–3 establish this relationship so that, when an XSLT processor sees the xsl: prefix, it knows to process the element as XSLT. Figure 4 shows how to interpret the namespace declaration in our example.

Figure 4

Figure 4 Defining a namespace reference for XSLT elements.

Deconstructing XSLT

So now that we can use namespaces to identify the XSLT elements, let’s walk through the code in Listing 3 to see how XSLT and XPath combine to generate our HTML.

  • Line 5: Here we inform the XSLT processor that we will be outputting HTML. This helps set up the output correctly, since the output of XSLT can be just about anything. Options here include HTML, XML, or text.
  • Line 7: <xsl:template match="/"> is the beginning of an xsl:template (rule). An XSLT processor works by trying to match templates against the XML. If a match occurs, the content of the template element is generated as output. In this template, we’re matching against /, which is XPath shorthand for the root of the document (refer to Figure 2). Since every document has a root, this rule always matches, and the content of this element is generated.
  • Lines 8–16: These lines specify the output given a successful match. Look carefully and you should be able to see that what’s being generated is the HTML for the web page we’re targeting, along with some XSLT inserted where we want details of the most popular books. As the HTML is generated, the XSLT on lines 17–22 is used to dip back into the XML and extract the book title, author, and ISBN, filling out the HTML list.
  • Lines 17–22: Here we see the XSLT that generates the actual list of favorite books. To loop over all the book titles in our XML, we use the powerful xsl:for-each element, which works just like a for loop in C++ or Java:
    <xsl:for-each select="/books/book/title">
  • Here our XPath select phrase (written as the value of the select attribute) tells XSLT to search from the root, find all books elements, find all their book children, and then collect all their title children. Behind the scenes, the XSLT processor gathers all the title elements and applies lines 18–21 to each one.
  • Lines 18–21: For each title located in our XML, we want to generate a single HTML list item of the following form:
    <li> ... </li>
  • Within each list item, we want to display the title, the last name of the author (in parentheses), and the ISBN. To accomplish this objective, we need to switch back to XSLT. However, keep in mind that since we’re technically within the context of one iteration of the XSLT for-each loop, when we ask for title, author, and ISBN our request will be relative to our current working title element (which is what we asked for in select="/books/book/title").

Because we’re already at a title element, we can obtain its value (the title of the book) by using this expression:

<xsl:value-of select="."/>

where the dot (".") is an XPath expression that means the value of the current node.

To obtain the last name of the author, though, we have to navigate back up the tree to the book element and then down to author/lname. Just like in UNIX or DOS, where .. is used to navigate up a directory hierarchy, XPath uses .. to move up the XML node hierarchy. Thus, to display the last name from our title context and surround the value with parentheses, we use this:

(<xsl:value-of select="../author/lname"/>)

To extract the isbn attribute value, which is part of the book element, we again need to go back up the tree (..) from our title element. To get the value of an attribute that’s part of an element, we use @ followed by the attribute’s name. The final piece to our dynamic output is the following:

<xsl:value-of select="../@isbn"/>

XPath Overview

XSLT makes use of XPath expressions to specify which parts of the input XML document to match against. In XSLT, whenever you see select = " .. ", the phrase inside the parentheses is XPath. We’ve already seen select ="/" (which matches against the root of a document). Additional slashes in XPath, much like the navigation through a file directory structure, move us down through child nodes in a tree.

Table 1 extends our knowledge of XPath by showing some matching expressions and how they’re commonly used in XSLT.

Table 1 Some XPath examples.

XPath Expression

What’s Matched




Every XML document has a root that conceptually sits above the top-level element, so this match always works.


The element books that is our top-level element.

Since there can only be one top-level element, only one element is returned


All the book elements that appear anywhere in the document.

In our example, book only appears as a child of books. If our document were more complex, with book elements appearing elsewhere, this XPath match would find them all.


All the title elements that are children of book, where book can appear anywhere in the document.



All the title elements that are two levels down from the top of the document.

Using the asterisk or star (*) selects every element that is within the preceding path.


Matches the attribute isbn in any tag in the document.

The @ symbol refers to attributes.


Matches the attribute isbn only when it appears in the book element, which can be anywhere in the document.



Matches every attribute in the entire document

* acts as a wildcard in XPath.


Matches all the book elements that have an attribute named isbn.

Using brackets [..] acts as a qualifier. Here we’re using attribute values to control the selection of elements. With our sample data, all the book elements are returned in the match.


Matches only the book elements that have this isbn value.

Here only one book element is returned.

  • + 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.


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.


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.


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.


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


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


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.


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.


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