Home > Articles > Web Services > XML

  • Print
  • + Share This
This chapter is from the book

3.4 Interface Versus Payload Semantics

Typically, an interaction between a client and a server (or a sender and a receiver) results in the execution of a transaction (or some other activity) on the receiving end. In order to determine the type of transaction or activity that was requested by the caller (or sender), it is necessary to specify the operation. This is normally performed in one of two ways: The requested transaction/activity can be encoded in the operation signature of the server component's interface, or it can be embedded in the message itself.

In the first case, the requested transaction (or other kind of activity) is defined by using self-descriptive function names such as saveCustomer(), retrieveCustomer(), or transferMoney(). RPC-style interfaces provide this type of semantically rich interface, which we refer to as interface semantics (see Figure 3-13).

Figure 3.13Figure 3-13 RPC-style interaction is typically based on interface semantics. Every procedure call has a meaningful name that indicates its purpose.

In the second case, the requested transaction is embedded directly into the message (see Figure 3-14). This can be done as part of the message header (if the MOM provides such a field as part of the message header data structure), or as part of the application specific payload. We refer to this as payload semantics.

Figure 3.14Figure 3-14 The name of a remote call with payload semantics has no functional meaning in its own right. The remote functionality required is encoded in the message that is sent. The receiver typically has to determine the function name and the dispatch message to the associated business function.

Payload semantics is widely used in the context of MOMs that provide APIs with functions such as MQGET()/MQPUT() or sendMessage()/onMessage()/receiveMessage() for the clients and servers to communicate with each other. The semantics of these functions is purely technical (see Figure 3-15).

Figure 3.15Figure 3-15 MOM is generally based on payload semantics. Functions such as sendMessage() and processMessage() are purely technical, without any business semantics.

Interface semantics provide users with well-defined interfaces that are intuitive and easy to understand. Changes to these interfaces require modifications to all applications that depend on the particular interface, even if they do not depend on the operation or argument that was added or changed. Payload semantics, on the other hand, result in systems where changes to message formats can have a potentially lesser impact on the different components of the system. New functionality can easily be added to a system by creating new messages types. Consumers that are not dependent on the new messages types remain unaltered. Thus, payload semantics results in a weaker coupling at the type level.

The choice of interface semantics versus payload semantics is not an obvious one, as each approach has its pros and cons. Strongly typed languages, such as Java, limit the flexibility of the programmer by applying strict type checking at compile time. Almost all dependencies caused by the change of a type in the system can be discovered at compile time, thus significantly reducing the number of runtime errors. Weakly typed languages, such as TCL, offer much more flexible data manipulation, often based on string manipulation. These types of languages are generally used for scripting, especially in Web environments, where fast results are required.

However, the application of interface semantics and payload semantics cannot be viewed in black-and-white terms. While RPCs are not restricted to pure functional call semantics, neither are MOMs limited to payload semantics. This can be illustrated with one insightful example. Consider an RPC call such as transferMoney(). The transmitted data can significantly contribute to the determination of the code that is executed:

String transferMoney (amount: decimal; cur, accFrom, accTo: String);
{
  switch (cur)
  case 'EUR':
   handleEurTransfer (amount, accFrom, accTo);
  case 'GBP':
   handleGbpTransfer (amount, accFrom, accTo);
  case 'USD':
   handleUsdTransfer (amount, accFrom, accTo);

  . . .
}

Going one step further, it is possible to remove all interface semantics from an RPC-style interface. In the following example, a service supports exactly one function, executeService(). This function has only one parameter, a plain string. This string encodes all functional parameters and the requested functionality:

String executeService (message: String);
{
  int i = determineFunctionNumber (message);

switch (i)
  case 1:
   handleCase1 (message);
  case 2:
   handleCase2 (message);
  case 3:
   handleCase3 (message);
  . . .
}

3.4.1 Document-Centric Messages

With the emergence of self-descriptive data structures such as XML, an approach to handling message types referred to as document-centric has become popular. Document-centric messages are semantically rich messages where the operation name, its parameters, and the return type are self-descriptive. However, the passed parameters and returned object can be extremely flexible and can include any number of optional parameters. SOAP (Simple Object Access Protocol) is a technology that is particularly suitable for this type of solution. As long as the underlying XML Schemas impose only loose constraints on the document structure, the parameters can be extended in any manner required without breaking compatibility with previous software versions. Consider the following example that describes the booking of a flight. It is straightforward to enhance the protocol with additional parameters, such as the time of day of the flight, the date and time of arrival, or the verbose names of the airports. As long as these fields are not required, the previous version of the protocol, in addition to all software that relies on that version, remains totally valid. Because this type of communication includes a structured document in both reply and response, it is called document-driven communication:

<SOAP-ENV:Envelope xmlns:SOAP-ENC="http://schemas.xmlsoap.org/
soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
 xmlns:xsd="http://www.w3.org/2001/XMLSchema"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> 
  <SOAP-ENV:Body> 
   <ns1:bookFlight xmlns:ns1="http://www.openuri.org/"> 
     <ns1:inbound> 
      <ns1:flightNumber>LH400</ns1:flightNumber>
      <ns1:flightDate>2003-11-08</ns1:flightDate>
      <ns1:isConfirmed>false</ns1:isConfirmed>
     </ns1:inbound>
     <ns1:outbound> 
      <ns1:flightNumber>LH401</ns1:flightNumber>
      <ns1:flightDate>2003-11-17</ns1:flightDate>
      <ns1:isConfirmed>false</ns1:isConfirmed>
     </ns1:outbound>
     <ns1:passenger> 
      <ns1:Passenger> 
        <ns1:firstName>Karl</ns1:firstName>
        <ns1:lastName>Banke</ns1:lastName>
        <ns1:birthday>1970-08-05</ns1:birthday>
      </ns1:Passenger>
     </ns1:passenger>
   </ns1:bookFlight>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>
  • + Share This
  • 🔖 Save To Your Account

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