Home > Articles > Web Development

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

7.4 Service Abstraction

The appropriate level of abstraction at which services are described achieves additional agility and alignment between business and IT areas of an enterprise. Abstracting information means taking technical details out of a problem to be solved on a higher level. Since the beginning of computer technology, information has been abstracted into higher levels in a number of ways, for example:

  • Assembler constructs, which are instructions for a processor, are translated into a series of 1 and 0.
  • Operating systems offer access to system resources and APIs that encapsulate lower-level constructs.
  • Programming languages, such as Java, introduce a more abstract way of describing logic, which is then compiled into a format that the operating system can understand.

Service-orientation continues the evolution of higher-level abstraction use to make creating and changing solutions easier. For example, a business process defined with WS-BPEL describes a sequence of service invocations and the data flows between them by expressing this sequence in XML form without writing any actual code. A side effect of this increased abstraction is the ability to utilize visual programming tools that support the creation of process definitions via drag-and-drop-style interfaces. The Service Abstraction principle advocates that the technical details of the technology platform underlying a service contract are hidden from the service consumer. It also promotes hiding non-essential details about the service itself.

Abstracting Technology Details

The service contract represents an abstraction of the functionality implemented in the service logic. Included in this notion is the abstraction of technical resources utilized to fulfill a service’s functionality.

Filenames, database tables, machine names, and network addresses should be omitted from the service contract and completely hidden from service consumers. Given that a service contract should always be designed with a particular business purpose in mind, this should never be a problem.

Concerns arise when services are generated straight out of existing code, because technology details which should have otherwise been abstracted away will often be exposed. For example, whether or not a service is implemented in Java or running in a Java environment such as Java EE should be completely irrelevant to the service consumer.

Hiding Service Details

Maximum flexibility is achieved when the technology used to implement a service and additional details about that service are hidden, which can be divided into information about the input or output message format and contextual information.

Hiding the information about the input or output message format may seem counterintuitive. If a service’s input and output messages are hidden, what is left to put into the service contract? Message formats can be abstracted to a generic level without surrendering the message definition altogether.

For example, assume a Credit Check service receives customer information as input. The customer information can be defined and represented by a Customer complex type in the XML schema definition to a detailed level, adding constraint information to each attribute and element of that schema. The length of the lastName character field is limited to 35 characters in Example 7.36.

Example 7.36 XML schema definition with added constraint inheritance can limit the lastName field to a set number of characters.

<complexType name="Customer">
  <sequence>
    <element name="firstName" type="string"/>
    <element name="lastName">
      <simpleType>
        <restriction base="string">
          <length value="35"/>
        </restriction>
      </simpleType>
    </element>
    <element name="customerNumber" type="string"/>
  </sequence>
</complexType>

The XML schema definition in Example 7.36 maps to a Java class, Customer.java, as seen in Example 7.37. (The generated Javadoc comments are omitted.)

Example 7.37 The generated Java type does not include the schema type restriction.

public class Customer {
  @XmlElement(required = true)
  protected String firstName;
  @XmlElement(required = true)
  protected String lastName;
  @XmlElement(required = true)
  protected String customerNumber;

  public String getFirstName() {
    return firstName;
  }
  public void setFirstName(String value) {
    this.firstName = value;
  }
  public String getLastName() {
    return lastName;
  }
  public void setLastName(String value) {
    this.lastName = value;
  }
  public String getCustomerNumber() {
    return customerNumber;
  }
  public void setCustomerNumber(String value) {
    this.customerNumber = value;
  }
}

On the opposite end of the abstraction spectrum would be a message definition stating that the incoming message is an XML document with a root Customer element. No information is given about individual attributes or elements contained in the document, as seen in Example 7.38.

Example 7.38 An XML schema definition using the <any/> element

<complexType name="Customer">
  <sequence>
    <any/>
  </sequence>
</complexType>

The generic type definition leads to a generic Java class, as shown in Example 7.39.

Example 7.39 The <any/> element is mapped to java.lang.Object.

public class Customer {
  @XmlAnyElement(lax = true)
  protected Object any;
  public Object getAny() {
    return any;
  }
  public void setAny(Object value) {
    this.any = value;
  }
}

Hiding service details and increasing what is abstracted about a service may always appear to be a prudent step. However, the service consumer is sometimes not provided with all of the necessary information on what exactly the service expects and what will be returned in response. Details of an interaction on both sides are left to be resolved at design-time or runtime (outside of the service contract).

In Example 7.38, the generic version states that a Customer object contains a java.lang.Object, which must be defined at runtime to allow for processing. Generally, more Java code must be written for errors that can occur at runtime. For XML payloads, this consideration is equally valid for SOAP and REST services, as the mechanics perform the same role for both in mapping XML to Java via a binding tool such as JAXB. An abstract service contract can be appropriate in some instances, such as utility services.

Contextual data can also be hidden, as this type of data is commonly about an interaction which does not contain any business-relevant payload information. When using SOAP-based Web services, SOAP header fields store contextual data, such as unique message identifiers, timestamps, and service consumer identity. For greater abstraction, detailed information about contextual header fields can be left out of the service contract altogether. This contextual information can be added or removed depending on the environment in which a service runs, is not relevant for its business purpose, and can often be left out of the contract.

For REST services, in the absence of any kind of a payload envelope, contextual information must be part of a resource representation. Such resource metadata can still be packaged inside specially designated header elements. The technical details of a service that are not part of the service interface, such as a WSDL or service-level information about response times and availability, can be abstracted. The technical details can be important to know, but often change and depend on a particular runtime environment and deployment of a service. For REST services, such service-level agreement characteristics can be described in a separate document.

Document Constraints

Non-technical information about a service cannot be articulated in a standard format. A generic example of this is a service-level agreement, but may also include other constraints about the usage of a service, valid ranges of input data beyond what can be expressed in WSDL and XML schema, and any additional applicable documentation.

A service can be implemented and deployed in different ways throughout an enterprise. As such, this documentation should not be directly linked with a service. Java, for example, is well suited for deployment on multiple platforms and operating systems. A Unix-based environment has different performance, scalability, and availability characteristics than a Windows-based system. Additionally, a Java EE application server can be leveraged to host the Java logic. A service instance can run on just one server instance on a small machine. As reuse of the service increases, the service instance can be moved to a clustered environment with greater computing power.

As per the Dual Protocols pattern, a Web service offered over HTTP can be later exposed via JMS for additional reliability requirements by particular service consumers. Abstract service contracts provide the freedom to make changes throughout the lifetime of the service, without breaking or violating previous versions. REST service implementations are synonymous with HTTP, making transport mechanism abstraction a non-issue. As the information about a service grows in abstraction, the service implementation and service consumer logic must become more flexible to anticipate future changes.

  • + 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