Home > Articles

XML—Extensible Markup Language

XML provides the foundation for enabling inter-application communication between disparate software systems. XML is a general-purpose markup language which allows developers to structurally describe data independent of specific software applications. The ability to independently describe data facilitates information exchange across organizations by making software applications easier to design, build, deploy, and maintain. Since XML is self-describing, the applications that use it to communicate do not need to worry about specific formatting.

It is easy to learn how to create and read XML documents. They are similar in appearance to HTML and typically include standard English terminology instead of code language. Listing 3.1 shows an XML document that describes several pets found in a typical family household.

Listing 3.1  An XML Description of Household Pets

<household>
    <pets>
        <pet type="cat">
            <breed>Domestic Short Hair</breed>
            <name>Daisy</name>
            <color>Brown</color>
            <weight>16 pounds</weight>
        </pet>
        <pet type="cat">
            <breed>Domestic Short Hair</breed>
            <name>Hana</name>
            <color>BrownishBlack</color>
            <weight>6 pounds</weight>
        </pet>
        <pet type="dog">
            <breed>Australian Shepard</breed>
            <name>Nellie</name>
            <color>Blue Merle</color>
            <weight>24 pounds</weight>
        </pet>
    </pets>
</household>

The listing above shows that XML documents are comprised of elements and attributes to create a structured representation of data. This particular set of data describes three household pets, two cats and a dog, and contains four pieces of information for each pet. The <household> element is the root element and contains all other elements and attributes in the household pet document. The <pets> tag is a collection of individual <pet> tags, each describing an individual pet. The type attribute on the <pet> element allows us to further describe a pet using simple name-value pairs. Each XML tag can have zero or more name-value pairs to indicate the specific properties of the tag instance.

When authoring your own XML documents there are a few key guidelines to follow in order to create well-formed XML:

  • Each element must have an end tag.

  • Elements cannot overlap.

  • Attribute values must be enclosed in quotation marks.

  • Documents must have a unique root node.

By following these four simple rules you can create highly descriptive and well-formed documents that represent a variety of business data. Many companies have already published XML schemas for use in a specific industry or with specific types of data.

XML and HTML

As shown above, XML is used to describe the content of data. Contrast this to HTML, Hypertext Markup Language, which details how to display data in a web browser. Using HTML, we can tell a browser to display data using a particular font type and size, or act as a hyperlink for site navigation. Using XML together with HTML, we can extend the value of business data by separating content from presentation. This allows a single set of data to be reused in multiple presentations and a single presentation to display multiple sets of data.

One of the benefits of using a standard markup language such as XML to represent our data is that we can easily integrate data from different sources. For example, we can aggregate content from relational databases, spreadsheets, text files, or legacy corporate applications, into a single XML document. This document can then be merged with HTML for robust presentation in a web browser. Instead of displaying in a web browser, we could also deliver the XML to a software application in a different enterprise thus providing a link between the two standalone applications and producing a truly distributed software system.

As we shall see shortly, XML is the technology which provides the infrastructure for distributed software concepts like Simple Object Access Protocol (SOAP) and Web services.

NOTE

A complete discussion of XML is beyond the scope of this chapter, as entire books have been written about XML. Our intention isn't to create XML experts but instead merely to provide a basic introduction to XML. For those interested in learning more please visit the following web links for additional information on XML:

XSD Schema

One question we need to address is, "How do we define our own XML document and data structures?" The answer is via an XSD schema. The XML Schema Definition (XSD) is a language, based on XML, that allows us to define the structure and data types for XML documents. When we author an XSD schema we actually use a set of elements, attributes, and data types that conform to the World Wide Web Consortium (W3C) XSD Schema Definition language. This specification serves as the blueprint for authoring XSD schemas, and in turn, schemas serve as blueprints for XML document instances.

XSD schemas are a bit more difficult to create than simple XML documents, since XSD schemas serve as blueprints for XML documents. The relationship between XSD schemas and XML documents is similar to that between classes and objects. XML documents are instances of XSD schemas, just as objects are instances of classes in object oriented programming.

Since XSD schemas are defined using XML, all schemas must have a top-level node. The W3C specification states this node must be the <schema> element and its definition must include the www.w3.org/2001/XMLSchema namespace.

NOTE

According to the W3C standards body, "An XML namespace is a collection of names, identified by a URI reference, which are used in XML documents as element types and attribute names. XML namespaces differ from the `namespaces' conventionally used in computing disciplines in that the XML version has internal structure and is not, mathematically speaking, a set." See www.w3.org/TR/REC-xml-names/ for more information.

Since <schema> is the top-level node, all elements and attributes used to author a schema must appear between the begin and end <schema> tags. The specification also describes the exact elements and attributes authors may utilize to develop XSD schemas.

Let's work by example. Listing 3.2 shows the XSD schema that defines the household pet XML document that was studied earlier in the chapter.

Listing 3.2  Household Pets XSD Schema

<xsd:schema id="household" targetNamespace="" xmlns="" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-
microsoft-com:xml-msdata">
 <xsd:element name="household" msdata:IsDataSet="true">
   <xsd:complexType>
    <xsd:choice maxOccurs="unbounded">
     <xsd:element name="pets">
       <xsd:complexType>
        <xsd:sequence>
         <xsd:element name="pet" minOccurs="0" maxOccurs="unbounded">
           <xsd:complexType>
            <xsd:sequence>
             <xsd:element name="breed" type="xsd:string" minOccurs="0" 
msdata:Ordinal="0" />
             <xsd:element name="name" type="xsd:string" minOccurs="0" 
msdata:Ordinal="1" />
             <xsd:element name="color" type="xsd:string" minOccurs="0" 
msdata:Ordinal="2" />
             <xsd:element name="weight" type="xsd:string" minOccurs="0" 
msdata:Ordinal="3" />
            </xsd:sequence>
            <xsd:attribute name="type" type="xsd:string" />
            <xsd:attribute name="pets_Id" type="xsd:int" use="prohibited" />
           </xsd:complexType>
         </xsd:element>
        </xsd:sequence>
        <xsd:attribute name="pets_Id" msdata:AutoIncrement="true" 
type="xsd:int" msdata:AllowDBNull="false" use="prohibited" />
       </xsd:complexType>
     </xsd:element>
    </xsd:choice>
   </xsd:complexType>
   <xsd:unique name="Constraint1" msdata:PrimaryKey="true">
    <xsd:selector xpath=".//pets" />
    <xsd:field xpath="@pets_Id" />
   </xsd:unique>
   <xsd:keyref name="pets_pet" refer="Constraint1" msdata:IsNested="true">
    <xsd:selector xpath=".//pet" />
    <xsd:field xpath="@pets_Id" />
   </xsd:keyref>
 </xsd:element>
</xsd:schema>

As we can see, the schema (Listing 3.2) is more complex than its instance (Listing 3.1). Our household pet schema, like all schema, begins with the <schema> element. Looking through the listing we find <element> declarations for our household, pets, pet, breed, name, color, and weight elements, as well as an <attribute> element that defines the type attribute of the <pet> element. Properties such as MinOccurs and MaxOccurs define the minimum number of times a tag can occur. For instance, the <pet> tag has a MinOccurs value of 0 and an unbounded MaxOccurs value, indicating that for any household, there can be 0 or more pets.

NOTE

The XSD schema in Listing 3.2 was generated using the Microsoft .NET Framework XML schemas support utility (xsd.exe). This program allows solution developers to efficiently interoperate between schemas and .NET classes, and is available in the Microsoft .NET Framework SDK.

Up to this point we've discussed XML and studied a simple document instance. We've learned how the separation of content and presentation is important in bringing together data from different sources. We talked briefly about XSD Schema and looked at an example declaration for our household pet example. In the next section, we will discuss technologies that extend XML to create a new set of tools that facilitate inter-application communications.

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