Home > Articles

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

Aspects and Other Concerns

In the world of aspect-oriented language development, aspects have taken on different forms. Two are most prominent: the asymmetric and the symmetric approaches.

Asymmetric Separation

In the asymmetric school of thought, aspects are separate from the core functionality of a program. Aspects are encoded as events that are triggered before, after, or as a replacement for certain other events, or in certain situations are located in the core. They describe additional dynamic behavior of a system that will have an effect on the core functionality. In a distributed system, for instance, there may be a collection of domain-specific objects that need to be managed in terms of distribution, synchronization, and transaction management.

The core contains the structure and behavior relevant to the domain functionality of the system. Separate from that core are aspects like the distribution of the objects in the system, the synchronization scheme associated with the methods belonging to those objects, and the wrapping of a set of operations into a single transaction. These are described in a separate module (each in its own aspect) and are invoked at certain strategic points in the execution of the core of the program. For instance, before certain methods are executed, the synchronization aspect may be used. Or, transaction-handling processing is initiated before and after the set of operations that make up a single transaction. In our banking example, as illustrated in Figure 1–2, the core is the set of banking-specific classes, and the aspect is a separate transaction handling entity.

Figure 1.2

Figure 1–2 Aspects and core in the asymmetric paradigm.

At a conceptual level, aspects have two important properties in this scheme. First, the aspect will only be triggered because of some execution in the core—for example, transaction handling is required only when changes are made to the balances of accounts. Second, the aspect is highly likely to be triggered in many parts of the system—it really is not generally all that useful to separate design/code into an aspect if it is executed in only one part of a system.

Table 1–1 provides definitions of the terms as typically used in this paradigm.

Table 1–1 Definition of Terms in the Asymmetric Separation Paradigm

Term

Description

Crosscutting

Concern behavior that is triggered in multiple situations.

Advice

The triggered behavior.

Aspect

The encapsulation of the advice and the specification of where the advice is triggered.

Core

The traditional object-oriented part of the system to which aspects are applied.

Joinpoint

A possible execution point that triggers advice.

Pointcut

A predicate that can determine, for a given joinpoint, whether it is matched by the predicate

Weaving

Applying the advice to the core at the joinpoints that match the pointcut statements in the aspects.

Symmetric Separation

In the symmetric separation model, in addition to the modularization of aspects, the core as described above is also analyzed for further modularization. Consider the core banking system from Figure 1–1. This example illustrates a small amount of real banking functionality with three basic features or concerns: transferring funds between two accounts, applying charges to an account, and applying interest to an account. In a real banking system, not only are there many other features, but these three features are subject to a significant number of banking rules. These rules depend on many different properties, such as the type of account, type of customer, legal and tax concerns (national/EU or state/federal, etc.), and so on. Figure 1–3 illustrates how it is possible that each feature is likely to result in many other methods that are likely to have an impact across the core set of banking classes.

Figure 1.3

Figure 1–3 Multiple concerns in the asymmetric core.

Figure 1–3 necessarily depicts just a small proportion of the possible impact of each of these three features on the classes. As you can see, there are multiple methods in the account classes that handle the business rules. The , , and classes all have many methods related to checking charges and checking interest. It may appear as if those could just be swept into the superclass. Unfortunately, that’s not the case. Each of the accounts handles those rules very differently, and so the functionality has to be present in each of them.

We hope you can visualize the potential real impact of including the full behavior not just of these three features, but also of all banking features on the core system. In the symmetric paradigm, different features of the system can be modularized into separate programs, as illustrated at the design level in Figure 1–4.

Figure 1.4

Figure 1–4 Separation of different features in the symmetric paradigm.

An entire system is therefore made up of bits of separate functionality that could be thought of as features or concerns. These can then be recombined in various ways to form a functioning whole. With this approach, a set of distributed objects would be formed by composing bits of basic object functionality together with bits of distribution functionality and synchronization functionality and transaction functionality.

At first glance, the duplication present in the symmetric approach looks as if it actually worsens scattering. For instance, all of the concerns except for the Transaction Management concern in Figure 1–4 have an class as well as a class, a class, and a class. This duplication is required in the symmetric approach in order to provide a complete view of the system from the perspective of a particular concern. The completeness of the view enhances separate understandability of a particular concern in the system.5 This understandability is achieved through increases in locality: Only and all relevant functionality for a concern is present within the concern module. Concern maintainability is also considered enhanced because of this functional locality. It is true that altering every method belonging to a class would require visiting many concerns, but since maintenance efforts are often performed to address particular concerns, the locality of all concern functionality within an identifiable group of modules is actually a help to system maintainability.

Of course, the symmetric approach can be applied on a continuum. It is unnecessary to keep minute concerns separate, just as it is unnecessary to bundle all the core concerns together. This spectrum is one that the developer is encouraged to explore, as each extreme has its own trade-offs and advantages.

The terms for the symmetric approach are given in Table 1–2. Notice that the terminology for this approach is different from the asymmetrical approach described above. Crosscutting, for instance, takes a wider stance: that it is widely triggered functionality, but also that structure and behavior (concepts) related to a particular concern are scattered throughout the system.

Table 1–2 Definition of Terms in the Symmetric Separation Paradigm

Term

Definition

Concern

Some "kind" of functionality in your system. This could be a feature or a type of processing.

Crosscutting

A concern triggered in multiple situations or whose structure and behavior are scattered across the code base and tangled with code related to other concerns.

Composition

Combining the separately implemented concerns to form a functioning system.

  • + 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