Home > Articles > Web Services > XML

This chapter is from the book

3.6 Quality of Service

Specifications in this domain are related to the quality of the experience associated with interaction with a Web service. The services in this layer specify the requirements that are associated with the overall reliability of Web services. The specific issues involving this layer include security, reliability of message delivery, and support for transactions (guaranteeing and agreeing on the outcome of a business application).

3.6.1 WS-Security

Security is of fundamental concern in enterprise computing. WS-Security is the basic building block for secure Web services. Today, most distributed Web services rely on transport-level support for security functions (for example, HTTPS and BASIC-Auth authentication). These approaches to security provide a basic minimum for secure communication, and the level of function they provide is significantly less than that provided by existing middleware and distributed environments. WS-Security uses existing security models (such as Kerberos and X509). The specifications concretely define how to use the existing models in an interoperable way. Multihop, multiparty Web service computations cannot be secure without WS-Security.

Security relies on predefined trust relationships. Kerberos works because participants trust the Kerberos Key Distribution Center. Public Key Infrastructure (PKI) works because participants trust the root certificate authorities. WS-Trust defines an extensible model for setting up and verifying trust relationships. The key concept in WS-Trust is a Security Token Service (STS). An STS is a distinguished Web service that issues, exchanges, and validates security tokens. WS-Trust allows Web services to set up and agree on which security servers they trust, and to rely on these servers.

Some Web service scenarios involve a short sporadic exchange of a few messages. WS-Security readily supports this model. Other scenarios involve long, multimessage conversations between the Web services. WS-Security also supports this model, but the solution is not optimal.

Protocols such as HTTP/S use public keys to perform a simple negotiation that defines conversation-specific keys. This key exchange allows more efficient security implementations and decreases the amount of information encrypted with a specific set of keys. WS-SecureConversation provides similar support for WS-Security. Participants often use WS-Security with public keys to start a conversation or session, and they use WS-SecureConversation to agree on session specific keys for signing and encrypting information.

WS-Federation allows a set of organizations to establish a single, virtual security domain. For example, a travel agent, an airline, and a hotel chain might set up such a federation. An end user who logs into any member of the federation has effectively logged into all of the members. WS-Federation defines several models for providing federated security through protocols between WS-Trust and WS-SecureConversation topologies. In addition, customers often have "properties" when they deal with an enterprise, and WS-Federation allows the setting up of a federated property space. This allows each participant to have secure controlled access to each member’s property information about the end users.

The WS-Security family of specifications is discussed in detail in Chapters 12, "Security," and 13, "Advanced Security."

3.6.2 Reliable Messaging

In the Internet world, communication channels are typically unreliable. Connections break, messages fail to be delivered or are delivered more than once, and perhaps in a different sequence to that in which they were sent. Communication can become even more of an issue when the exchange of messages spans multiple transport layer connections. Although techniques for ensuring reliable delivery of messages are reasonably well understood and available in some messaging middleware products today (such as IBM WebsphereMQ), messaging reliability is still a problem. If messaging reliability is addressed by Web service developers who are incorporating techniques to deal with this directly into the services they develop, there is no guarantee that developers of different Web services will make the consistent choices about the approach to adopt. The outcome might not guarantee end-to-end reliable interoperable messaging. Even in cases in which the application developers defer dealing with the reliable messaging to messaging middleware, different middleware products from different suppliers do not necessarily offer a consistent approach to dealing with the problem. Again, this might preclude reliable message exchange between applications that are using different message-oriented middleware.

WS-ReliableMessaging addresses these issues and defines protocols that enable Web services to ensure reliable, interoperable exchange of messages with specified delivery assurances. The specification defines three basic assurances:

  • In-order delivery—The messages are delivered in the same order in which they were sent.

  • At least once delivery—Each message that is sent is delivered at least one time.

  • At most once delivery—No duplicate messages are delivered.

You can combine these assurances to give additional ones. For example, combining at least once and at most once gives exactly one delivery of a message. The protocol enables messaging middleware vendors to ease application development and deployment for Web services by providing services that implement these protocols, possibly layered over their existing proprietary message exchange protocols. WS-Reliable Messaging protocols allow different operating and middleware systems to reliably exchange messages, thereby bridging different infrastructures into a single, logically complete, end-to-end model for Web services reliable messaging.

WS-ReliableMessaging is discussed in detail in Chapter 10, "Reliable Messaging."

3.6.3 Transactions

Dealing with many of today’s business scenarios necessitates the development of applications that consist of multiple Web services exchanging many messages. An example might be a group of financial institutions setting up a financial offering that involves insurance policies, annuities, checking accounts, and brokerage accounts. Such applications can be complex, executing across heterogeneous, loosely coupled distributed systems that are prone to failure, and introducing significant reliability problems. For such applications, you must deal with the failure of any component Web service of the application within the context of the whole application. A coordinated orchestration of the outcome of the participating services that make up the business application is essential so that a coherent outcome of the whole business application can be agreed upon and guaranteed. Therefore, it is important that the Web services involved are able to do the following:

  • Start new tasks, the execution and disposition of which are coordinated with other tasks.

  • Agree on the outcome of the computation. For example, does everyone agree that the financial packages were set up?

WS-Coordination, WS-AtomicTransaction, and WS-BusinessActivity define protocols that are designed specifically to address these requirements.

WS-Coordination is a general mechanism for initiating and agreeing on the outcome of multiparty, multimessage Web service tasks. WS-Coordination has three key elements:

  • A coordination context—This is a message element that is associated with exchanges during the interaction of Web services. This coordination context contains the WS-Addressing endpoint reference of a coordination service, in addition to the information that identifies the specific task being coordinated.

  • A coordinator service—This provides a service to start a coordinated task, terminate a coordinated task, allow participants to register in a task, and produce a coordination context that is part of all messages exchanged within a group of participants.

  • An interface—Participating services can use the interface to inform them of an outcome that all of the participants have agreed upon.

Although WS-Coordination is a general framework and capability, WS-AtomicTransaction and WS-BusinessActivity are two particular protocols that compose with and extend the WS-Coordination protocol to define specific ways to reach overall outcome agreement. They extend this framework to allow the participants in the distributed computation to determine outcome robustly .

WS-AtomicTransaction defines a specific set of protocols that plug into WS-Coordination to implement the traditional two-phase atomic ACID transaction protocols. However, traditional atomic transactions and the WS-AtomicTransaction protocol are not always suitable. For example, this protocol is generally not appropriate for use with many types of business transactions. Transaction protocols for business transactions have to deal with long-lived activities. These differ from atomic transactions in that such activities can take much longer to complete. Therefore, to minimize latency of access by other potential users of the resources being used by Web services participating in the activity, you need to make the results of interim operations visible to others before the overall activity has completed. In light of this, you can introduce mechanisms for fault and compensation handling to reverse the effects of tasks that were completed previously within a business activity (such as compensation or reconciliation). WS-BusinessActivity defines a specific set of protocols that plug into the WS-Coordination model to provide such long-running, compensation-based transaction protocols. For example, although WS-BPEL defines a transaction model for business processes, it is WS-BusinessActivity that specifies the corresponding protocol rendering. This, again, is an example for the composeability of the Web services specifications.

WS-Coordination and Transaction specifications are covered in detail in Chapter 11, "Transactions."

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