Home > Articles > Programming > Java

This chapter is from the book

SOAP Envelope Framework

The most important part that SOAP specifies is the envelope framework. Although it consists of just a few XML elements, it provides the structure and extensibility mechanisms that make SOAP so well suited as the foundation for all XML-based distributed computing. The SOAP envelope framework defines a mechanism for identifying what information is in a message, who should deal with the information, and whether this is optional or mandatory. A SOAP message consists of a mandatory envelope wrapping any number of optional headers and a mandatory body. These concepts are discussed in turn in the following sections.

SOAP Envelope

SOAP messages are XML documents that define a unit of communication in a distributed environment. The root element of the SOAP message is the Envelope element. In SOAP 1.1, this element falls under the http://schemas.xmlsoap.org/soap/envelope/ namespace. Because the Envelope element is uniquely identified by its namespace, it allows processing tools to immediately determine whether a given XML document is a SOAP message.

This certainly is convenient, but what do you trade off for this capability? The biggest thing you have to sacrifice is the ability to send arbitrary XML documents and perform simple schema validation on them. True, you can embed arbitrary XML inside the SOAP Body element, but naïve validation will fail when it encounters the Envelope element at the top of the document instead of the top document element of your schema. The lesson is that for seamless validation of arbitrary XML inside SOAP messages, you must integrate XML validation with the Web services engine. In most cases, the Web services engine will have to separate SOAP-specific from application-specific XML before validation can take place.

The SOAP envelope can contain an optional Header element and a mandatory Body element. Any number of other XML elements can follow the Body element. This extensibility feature helps with the encoding of data in SOAP messages. We'll discuss it later in this chapter in the section "SOAP Data Encoding Rules."

SOAP Versioning

One interesting note about SOAP is that the Envelope element does not expose any explicit protocol version, in the style of other protocols such as HTTP (HTTP/1.0 vs. HTTP/1.1) or WDDX (<wddxPacket version="1.0"> ... </wddxPacket>). The designers of SOAP explicitly made this choice because experience had shown simple number-based versioning to be fragile. Further, across protocols, there were no consistent rules for determining what changes in major versus minor version numbers truly mean. Instead of going this way, SOAP leverages the capabilities of XML namespaces and defines the protocol version to be the URI of the SOAP envelope namespace. As a result, the only meaningful statement that you can make about SOAP versions is that they are the same or different. It is no longer possible to talk about compatible versus incompatible changes to the protocol.

What does this mean for Web service engines? It gives them a choice of how to treat SOAP messages that have a version other than the one the engine is best suited for processing. Because an engine supporting a later version of SOAP will know about all previous versions of the specification, it has a range of options based on the namespace of the incoming SOAP message:

  • If the message version is the same as any version the engine knows how to process, the engine can just process the message.

  • If the message version is older than any version the engine knows how to process, the engine can do one of two things: generate a version mismatch error and/or attempt to negotiate the protocol version with the client by sending some information regarding the versions that it can accept.

  • If the message version is newer than any version the engine knows how to process, the engine can choose to attempt processing the message anyway (typically not a good choice) or it can go the way of a version mismatch error combined with some information about the versions it understands.

All in all, the simple versioning based on the namespace URI results in the fairly flexible and accommodating behavior of Web service engines.

SOAP Headers

Headers are the primary extensibility mechanism in SOAP. They provide the means by which additional facets can be added to SOAP-based protocols. Headers define a very elegant yet simple mechanism to extend SOAP messages in a decentralized manner. Typical areas where headers get involved are authentication and authorization, transaction management, payment processing, tracing and auditing, and so on. Another way to think about this is that you would pass via headers any information orthogonal to the specific information needed to execute a request.

For example, a transfer payment service only really needs from and to account numbers and a transfer amount to execute. In real-world scenarios, however, a service request is likely to contain much more information, such as the identity of the person making the request, account/payment information, and so on. This additional information is usually handled by infrastructure services (login and security, transaction coordination, billing) outside the main transfer payment service. Encoding this information as part of the body of a SOAP message will only complicate matters. That is why it will be passed in as headers.

A SOAP message can include any number of header entries (simply referred to as headers). If any headers are present, they will all be children of the SOAP Header element, which, if present, must appear as the first child of the SOAP Envelope element. The following example shows a SOAP message with two headers, Transaction and Priority. Both headers are uniquely identified by the combination of their element name and their namespace URI:

<SOAP-ENV:Envelope
  xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
  SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
   <SOAP-ENV:Header>
       <t:Transaction xmlns:t="some-URI" SOAP-ENV:mustUnderstand="1">
               12345
       </t:Transaction>
       <p:Priority xmlns:p="some-Other-URI">
               <ReallyVeryHigh/>
       </p:Priority>
   </SOAP-ENV:Header>
   <SOAP-ENV:Body>
      ...
   </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

The contents of a header (sometimes referred to as the header value) are determined by the schema of the header element. This allows headers to contain arbitrary XML, another example of the benefits of SOAP being an XML-based protocol. Compare it to protocols such as HTTP where header values must be simple strings, thus forcing any structured information to be somehow encoded to become a string. For example, cookie values come in a semicolon delimited format, such as cookie1=value1;cookie2=value2. It is easy to reach the limits of these simple encodings. XML is a much better way to represent this type of structured information.

Also, notice the SOAP mustUnderstand attribute with value 1 that decorates the Transaction element. This attribute indicates that the recipient of the SOAP message must process the Transaction header entry. If a recipient does not know how to process a header tagged with mustUnderstand="1", it must abort processing with a well-defined error. This rule allows for robust evolution of SOAP-based protocols. It ensures that a recipient that might be unaware of certain important protocol extensions does not ignore them.

Note that because the Priority header is not tagged with mustUnderstand="1", it can be ignored during processing. Presumably, this will be OK because a server that does not know how to process message priorities will assume normal priority.

You might have noticed that the SOAP body can be treated as a well-specified SOAP header flagged with mustUnderstand="1". Although this is certainly true, the SOAP designers thought that having a separation between the headers and body of a message does not complicate the protocol and is convenient for readability.

Before leaving the topic of headers, it is important to point out that, despite the obvious need for header extensions to support such basic distributed computing concepts such as authentication credentials or transaction information, there hasn't been a broad standardization effort in this area, with the exception of some security extensions that we'll review in Chapter 5. Some of the leading Web service vendors are doing interesting work, but the industry as a whole is some way away from agreeing on core extensions to SOAP. Two primary forces maintain this unsatisfactory status quo:

  • Most current Web service engines do not have a solid extensibility architecture. Therefore, header processing is relatively difficult right now. At the time of this writing, Apache Axis is a notable exception to this rule.

  • Market pressure is pushing Web service vendors to innovate in isolation and to prefer shipping software over coordinating extensions with partners and competitors.

Wider Web service adoption will undoubtedly put pressure on the Web services community to think more about interoperability and begin broad standardization in some of these key areas.

SOAP Body

The SOAP Body element immediately surrounds the information that is core to the SOAP message. All immediate children of the Body element are body entries (typically referred to simply as bodies). Bodies can contain arbitrary XML. Sometimes, based on the intent of the SOAP message, certain conventions will govern the format of the SOAP body. The conventions for representing RPCs are discussed later in the section "SOAP-based RPCs." The conventions for communicating error information are discussed in the section "Error Handling in SOAP."

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