Home > Articles > Data > DB2

Converting XML to Relational Data for Use in DB2

This chapter describes methods to convert XML documents to rows in relational tables, commonly known as shredding or decomposing of XML documents.
This chapter is from the book

This chapter describes methods to convert XML documents to rows in relational tables. This conversion is commonly known as shredding or decomposing of XML documents. Given the rich support for XML columns in DB2 you might wonder in which cases it can still be useful or necessary to convert XML data to relational format. One common reason for shredding is that existing SQL applications might still require access to the data in relational format. For example, legacy applications, packaged business applications, or reporting software do not always understand XML and have fixed relational interfaces. Therefore you might sometimes find it useful to shred all or some of the data values of an incoming XML document into rows and columns of relational tables.

In this chapter you learn:

  • The advantages and disadvantages of shredding and of different shredding methods (section 11.1)
  • How to shred XML data to relational tables using INSERT statements that contain the XMLTABLE function (section 11.2)
  • How to use XML Schema annotations that map and shred XML documents to relational tables (section 11.3)

11.1 Advantages and Disadvantages of Shredding

The concept of XML shredding is illustrated in Figure 11.1. In this example, XML documents with customer name, address, and phone information are mapped to two relational tables. The documents can contain multiple phone elements because there is a one-to-many relationship between customers and phones. Hence, phone numbers are shredded into a separate table. Each repeating element, such as phone, leads to an additional table in the relational target schema. Suppose the customer information can also contain multiple email addresses, multiple accounts, a list of most recent orders, multiple products per order, and other repeating items. The number of tables required in the relational target schema can increase very quickly. Shredding XML into a large number of tables can lead to a complex and unnatural fragmentation of your logical business objects that makes application development difficult and error-prone. Querying the shredded data or reassembling the original documents may require complex multiway joins.

Figure 11.1

Figure 11.1 Shredding of an XML document

Depending on the complexity, variability, and purpose of your XML documents, shredding may or may not be a good option. Table 11.1 summarizes the pros and cons of shredding XML data to relational tables.

Table 11.1. When Shredding Is and Isn't a Good Option

Shredding Can Be Useful When...

Shredding Is Not A Good Option When...

  • Incoming XML data is just feeding an existing relational database.
  • Your XML data is complex and nested, and difficult to map to a relational schema.
  • The XML documents do not represent logical business objects that should be preserved.
  • Mapping your XML format to a relational schema leads to a large number of tables.
  • Your primary goal is to enable existing relational applications to access XML data.
  • Your XML Schema is highly variable or tends to change over time.
  • You are happy with your relational schema and would like to use it as much as possible.
  • Your primary goal is to manage XML documents as intact business objects.
  • The structure of your XML data is such that it can easily be mapped to relational tables.
  • You frequently need to reconstruct the shredded documents or parts of them.
  • Your XML format is relatively stable and changes to it are rare.
  • Ingesting XML data into the database at a high rate is important for your application.
  • You rarely need to reconstruct the shredded documents.
  • Querying or updating the data with SQL is more important than insert performance.

In many XML application scenarios the structure and usage of the XML data does not lend itself to easy and efficient shredding. This is the reason why DB2 supports XML columns that allow you to index and query XML data without conversion. Sometimes you will find that your application requirements can be best met with partial shredding or hybrid XML storage.

  • Partial shredding means that only a subset of the elements or attributes from each incoming XML document are shredded into relational tables. This is useful if a relational application does not require all data values from each XML document. In cases where shredding each document entirely is difficult and requires a complex relational target schema, partial shredding can simplify the mapping to the relational schema significantly.
  • Hybrid XML storage means that upon insert of an XML document into an XML column, selected element or attribute values are extracted and redundantly stored in relational columns.

If you choose to shred XML documents, entirely or partially, DB2 provides you with a rich set of capabilities to do some or all of the following:

  • Perform custom transformations of the data values before insertion into relational columns.
  • Shred the same element or attribute value into multiple columns of the same table or different tables.
  • Shred multiple different elements or attributes into the same column of a table.
  • Specify conditions that govern when certain elements are or are not shredded. For example, shred the address of a customer document only if the country is Canada.
  • Validate XML documents with an XML Schema during shredding.
  • Store the full XML document along with the shredded data.

DB2 9 for z/OS and DB2 9.x for Linux, UNIX, and Windows support two shredding methods:

  • SQL INSERT statements that use the XMLTABLE function. This function navigates into an input document and produces one or multiple relational rows for insert into a relational table.
  • Decomposition with an annotated XML Schema. Since an XML Schema defines the structure of XML documents, annotations can be added to the schema to define how elements and attributes are mapped to relational tables.

Table 11.2 and Table 11.3 discuss the advantages and disadvantages of the XMLTABLE method and the annotated schema method.

Table 11.2. Considerations for the XMLTABLE Method

Advantages of the XMLTABLE Method

Disadvantages of the XMLTABLE Method

  • It allows you to shred data even if you do not have an XML Schema.
  • For each target table that you want to shred into you need one INSERT statement.
  • It does not require you to understand the XML Schema language or to understand schema annotations for decomposition.
  • You might have to combine multiple INSERT statements in a stored procedure.
  • It is generally easier to use than annotated schemas because it is based on SQL and XPath.
  • You can use familiar XPath, XQuery, or SQL functions and expressions to extract and optionally modify the data values.
  • It often requires no or little work during XML Schema evolution.
  • The shredding process can consume data from multiple XML and relational sources, if needed, such as values from DB2 sequences or look-up data from other relational tables.
  • It can often provide better performance than annotated schema decompositions.
  • There is no GUI support for implementing the INSERT statements and the required XMLTABLE functions. You need to be familiar with XPath and SQL/XML.

Table 11.3. Considerations for Annotated Schema Decomposition

Advantages of the Annotated Schema Method

Disadvantages of the Annotated Schema Method

  • The mapping from XML to relational tables can be defined using a GUI in IBM Data Studio Developer.
  • It does not allow shredding without an XML Schema.
  • If you shred complex XML data into a large number of tables, the coding effort can be lower than with the XMLTABLE approach.
  • You might have to manually copy annotations when you start using a new version of your XML Schema.
  • It offers a bulk mode with detailed diagnostics if some documents fail to shred.
  • Despite the GUI support, you need to be familiar with the XML Schema language for all but simple shredding scenarios.
  • Annotating an XML Schema can be complex, if the schema itself is complex.

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