Home > Articles > Certification > Microsoft Certification

This chapter is from the book

Generating and Using XSD Schemas

In Chapter 2, "Creating and Manipulating DataSets," you learned how to create an XSD schema in the Visual Studio .NET user interface by dragging and dropping XML elements from the Toolbox. This method is useful when you need to create a schema from scratch. But there will be times when you want to create a schema to match an existing object. In this section, you'll learn about the methods that are available to programmatically generate XSD schemas.

Generating an XSD Schema

One obvious source for an XML schema is an XML file. An XML file can contain explicit schema information (in the form of an embedded schema), or it can contain implicit schema information in its structure. Here's a sample file, Products.xml, that contains embedded schema information:

<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:od="urn:schemas-microsoft-com:officedata">
<xsd:schema>
<xsd:element name="dataroot">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<xsd:element ref="Products"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
<xsd:element name="Products">
<xsd:annotation>
<xsd:appinfo/>
</xsd:annotation>
<xsd:complexType>
<xsd:sequence>
<xsd:element name="ProductID" od:jetType="autonumber"
od:sqlSType="int" od:autoUnique="yes"
od:nonNullable="yes">
<xsd:simpleType>
<xsd:restriction base="xsd:integer"/>
</xsd:simpleType>
</xsd:element>
<xsd:element name="ProductName" minOccurs="0"
od:jetType="text" od:sqlSType="nvarchar">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:maxLength value="40"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
<dataroot
xmlns:xsi=
"http://www.w3.org/2000/10/XMLSchema-instance">
<Products>
<ProductID>1</ProductID>
<ProductName>Chai</ProductName>
</Products>
</dataroot>
</root>

If the file contains explicit schema information, you can use the DataSet object to read that information and create the corresponding schema as a separate file, as shown here:

' Load the XML file with inline schema info
Dim xtr As XmlTextReader = _
 New XmlTextReader("Products.xml")
' Read the schema (only) into a DataSet
Dim ds As DataSet = New DataSet()
ds.ReadXmlSchema(xtr)
' Write the schema out as a separate stream
Dim sw As StringWriter = New StringWriter()
ds.WriteXmlSchema(sw)
txtSchema.Text = sw.ToString()

The DataSet object must have the capability to read an XML schema so that it can construct a matching data structure in memory. The .NET Framework designers thoughtfully exposed this capability to you through the ReadXmlSchema and WriteXmlSchema methods of the DataSet object. But what if the file does not contain explicit schema information? It turns out that you can still use the DataSet object because this object also has the capability to infer an XML schema based on the data in an XML file. For example, here's how to use the DataSet object to infer a schema for the Books.xml file:

' Load an XML file with no schema information
Dim xtr As XmlTextReader = _
 New XmlTextReader("Books.xml")
' Read the schema (only) into a DataSet
Dim ds As DataSet = New DataSet()
Dim ns As String()
ds.InferXmlSchema(xtr, ns)
' Write the schema out as a separate stream
Dim sw As StringWriter = New StringWriter()
ds.WriteXmlSchema(sw)
txtSchema.Text = sw.ToString()

You have at least four ways to obtain XSD files for your applications:

  • You can use a file generated by an external application such as Microsoft SQL Server or Microsoft Access.

  • You can create your own schema files from scratch using the techniques you learned in Chapter 2.

  • You can extract inline schema information from an XML file using the DataSet.ReadXmlSchema method.

  • You can infer schema information from an XML file using the DataSet.InferXmlSchema method.

Using an XSD Schema

The prime use of a schema file is to validate the corresponding XML file. Although any XML file that conforms to the syntactical rules for XML is well-formed, this does not automatically make the file valid. A valid XML file is one whose structure conforms to a specification. This specification can be in the form of an XML schema or a Document Type Definition (DTD), for example. Any valid XML file is well-formed, but not every well-formed XML file is valid. The .NET Framework provides good support for validating XML files.

To validate an XML document, you can use the XmlValidatingReader class. This class provides an additional layer between the XmlReader and the XmlDocument. The extra layer validates the document as it is read in to the XmlDocument object. To use the XmlValidatingReader object to validate an XML document with an inline schema, you should supply a handler for any validation errors, as in this code sample:

Private Sub ValidateIt()
 ' Load a document with an inline schema
 Dim xtr As XmlTextReader = _
  New XmlTextReader("Products.xml")
 ' Prepare to validate it
 Dim xvr As XmlValidatingReader = _
  New XmlValidatingReader(xtr)
 xvr.ValidationType = ValidationType.Schema
 ' Tell the validator what to do with errors
 AddHandler xvr.ValidationEventHandler, _
  AddressOf ValidationHandler
 ' Load the document, thus validating
 Dim xd As XmlDocument = _
  New XmlDocument()
 xd.Load(xvr)
End Sub

Private Sub ValidationHandler( _
 ByVal sender As Object, _
 ByVal e As ValidationEventArgs)
 ' Dump any validation errors to the UI
 MessageBox.Show(e.Message)
End Sub

An inline schema cannot contain an entry for the root element of the document, so even when the document is otherwise valid, you'll get an error from that node. The XmlValidatingReader class is constructed so that it does not stop on validation errors. Rather, it continues processing the file but raises an event for each error. This enables your code to decide how to handle errors while still filling the XmlDocument object.

You can also validate an XML file against an external schema. To do this, you can load the schema and the XML file separately and tell the XmlValidatingReader class to compare one to the other:

Private Sub ValidateIt()
 ' Load a document with an external schema
 Dim xtr As XmlTextReader = _
  New XmlTextReader("Books.xml")
 ' Prepare to validate it
 Dim xvr As XmlValidatingReader = _
  New XmlValidatingReader(xtr)
 xvr.ValidationType = ValidationType.Schema
 ' Tell the validator what to do with errors
 AddHandler xvr.ValidationEventHandler, _
  AddressOf ValidationHandler
 ' Load the schema
 Dim xsc As XmlSchemaCollection = _
  New XmlSchemaCollection()
 xsc.Add("xsdBooks", "Books.xsd")
 ' Tell the validator which schema to use
 xvr.Schemas.Add(xsc)
 ' Load the document, thus validating
 Dim xd As XmlDocument = _
  New XmlDocument()
 xd.Load(xvr)
End Sub

Private Sub ValidationHandler( _
 ByVal sender As Object, _
 ByVal e As ValidationEventArgs)
 ' Dump any validation errors to the UI
 MessageBox.Show(e.Message)
End Sub

Schema files are not the only way to describe the structure of an XML file. An older standard for specifying structure is the Document Type Definition, or DTD. DTDs are part of the Standard Generalized Markup Language (SGML) standard, from which both HTML and XML derive. A DTD file lists the elements that may appear in an XML file, as in this example (Books.dtd):

<!ELEMENT Books (Book)* >
<!ELEMENT Book (Author, Title, Publisher) >
<!ATTLIST Book Pages CDATA #REQUIRED>
<!ELEMENT Author (#PCDATA)>
<!ELEMENT Title (#PCDATA)>
<!ELEMENT Publisher (#PCDATA)>

To use a DTD file as the schema for an XML file, you include a DOCTYPE node in the XML file:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE Books SYSTEM "books.dtd">
<Books>
 <Book Pages="1046">
  <Author>Delaney, Kalen</Author>
  <Title>Inside Microsoft SQL Server 2000</Title>
  <Publisher>Microsoft Press</Publisher>
 </Book>
 <Book Pages="1000">
  <Author>Gunderloy. Michael</Author>
  <Title>ADO and ADO.NET Programming</Title>
  <Publisher>Sybex</Publisher>
 </Book>
 <Book Pages="484">
  <Author>Cooper, James W.</Author>
  <Title>Visual Basic Design Patterns</Title>
  <Publisher>Addison Wesley</Publisher>
 </Book>
</Books>

The XmlValidatingReader class can validate an XML document for conformance with a DTD, as in the following sample code:

Private Sub ValidateIt()
 ' Load a document with an external schema
 Dim xtr As XmlTextReader = _
  New XmlTextReader("Books.xml")
 ' Prepare to validate it
 Dim xvr As XmlValidatingReader = _
  New XmlValidatingReader(xtr)
 xvr.ValidationType = ValidationType.DTD
 ' Tell the validator what to do with errors
 AddHandler xvr.ValidationEventHandler, _
  AddressOf ValidationHandler
 ' Load the document, thus validating
 Dim xd As XmlDocument = _
  New XmlDocument()
 xd.Load(xvr)
End Sub

Private Sub ValidationHandler( _
 ByVal sender As Object, _
 ByVal e As ValidationEventArgs)
 ' Dump any validation errors to the UI
 MessageBox.Show(e.Message)
End Sub

The only difference between validating against a schema file and validating against a DTD is in the constant chosen for the ValidationType property of the XmlValidatingReader.

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