Home > Articles > Software Development & Management > Agile

Like this article? We recommend

Short Comparison with XP

Reading the introductions to FDD and XP reveals many similar factors driving the development of the two processes:

  • Traditional heavy processes with long "analysis phases" are unworkable for projects running on Internet time; business requirements are changing monthly if not weekly.

  • Software continues to be delivered late and over budget with less useful functionality than first envisioned.

Both FDD and XP are designed to enable teams to deliver results faster without compromising quality. Both processes are highly iterative and results-oriented. They're both people-focused instead of document-focused (no more thousand-page specifications to write). Both dismantle the traditional separation of domain and business experts/analysts from designers and implementers; analysts are dragged out of their abstractions and put in the same room as developers and users. These new processes, together with new tools and techniques, are enabling and encouraging analysis, design, code, test, and deployment to be done concurrently.

So where do FDD and XP differ?

Team Sizes

"XP is designed to work with projects that can be built by teams of two to ten programmers, that aren't sharply constrained by the existing computing environment, and where a reasonable job of executing tests can be done in a fraction of a day." [Beck]

FDD was first used with a team of 16–20 developers of varying abilities, cultural backgrounds, and experience: four chief programmers (CPs), sixteen class owners split into user interaction (UI), problem domain (PD), and data management (DM) teams. FDD is designed to scale to much larger team sizes. The limiting factor is the number of available CPs. Chief programmer teams have been proven in practice to scale well to much larger project teams (by the authors of FDD and independently [Brooks]).

Metaphor and Model

The XP process begins with the business writing stories on index cards. A story is something that the system needs to do. Development then estimates the time required to implement each story. The whole project is guided by a system metaphor, "an overall story that everyone—customers, programmers, and managers—can tell about how the system works" [Beck]. The business selects the subset of stories that will form the next release and development makes a delivery commitment. Development splits each of the stories into a number of tasks. Each developer accepts responsibility for a set of tasks.

Replace stories with domain walkthroughs and tasks with features and it sounds very similar to the first three activities in FDD.

The enormous difference between XP and FDD is FDD's additional development of an overall domain object model. As developers learn of requirements they start forming mental images of the system, making assumptions and estimating on that basis. Developing an overall domain object model forces those assumptions out into the open, misunderstandings are resolved, and a more complete, common understanding is formed.

XP uses the analogy of driving a car. Driving requires continual little course adjustments; you can't simply point the car in the right direction and press the accelerator. A domain object model is the map to guide the journey; it can prevent you from driving around in endless circles. The domain object model provides an overall shape to which to add function, feature by feature.

The domain object model enables feature teams to produce better designs for each group of features. This reduces the number of times that a team has to refactor their classes to add a new feature. Reducing the time spent refactoring increases the time that can be spent adding new features.

Collective Ownership or Class Ownership?

XP promotes collective ownership of code; any developer can add to or alter any piece of source code as needed. But collective ownership usually degenerates into non-ownership as the number of people involved grows. Small communes often work; larger communes rarely work for any length of time. XP claims three benefits from collective code ownership:

  • We avoid waiting for someone to make a change we need in their code.

  • Overly complex code is eliminated because anyone who finds such code will try to simplify it. Knowing this, developers are less likely to add complexity that they can't justify.

  • Collective ownership spreads knowledge of a system throughout the team, reducing risk if a crucial team member leaves.

Feature teams also solve these problems, while keeping the well-established benefits of individual code ownership:

  • By definition, all the owners of classes needing updates for the development of a particular feature are members of the feature team. In other words, the feature team owns all the code that needs changing for a particular feature. This minimizes waiting for someone else to modify their code.

  • All low-level design in FDD is done within feature teams (Design by Feature). The irritating "development by surprise" problem, in which a developer delivers code that's different from agreed design, is caught at code inspection by the feature team and rejected. Overly complex code is caught in the same way, before it enters the system.

  • Although class owners work only on the classes they own, owners of closely associated classes frequently work in the same feature team. They get to know those closely associated classes. Knowledge is clustered rather than randomly scattered.

XP also assumes that short integration and testing cycles means a low rate of collisions from developers updating the same piece of source code. For larger numbers of developers and systems, this is obviously less likely to be true.

Inspections and Pair Programming

Design and code inspections, when done well, are proven to remove more defects than testing. Secondary benefits include the following:

  • Education. Developers learn techniques from each other.

  • Coding standard enforcement. Conformance is checked.

XP uses pair programming to provide a continuous level of design and code inspection. All low-level design and coding is done in pairs. This is obviously better than individual developers delivering code without any form of inspection.

FDD promotes more formal inspections by feature teams; the level of formality is left to the chief programmer's discretion. This takes more time, but it has added advantages over pair programming:

  • Fresh eyes to look at the code, catching bad assumptions made by the coder(s).

  • A chief programmer to ensure that the techniques learned are good techniques. Yes, developers can easily teach each other bad habits as well as good habits.

  • Change of pace for developers—an hour or so away from the terminal (assuming the common practice of printing source code for inspection).

There's no reason why members of feature teams can't pair up during coding when this is desirable. It's not unusual to see two members of a feature team working together where care is needed. One of the great things about feature teams is that a feature is complete only when the team is finished—and not when any one individual is finished. It's in the team members' own interest to help each other.


Correctness in XP is defined by the running of unit and functional tests. FDD takes unit testing almost for granted as part of Build by Feature. FDD doesn't define the mechanisms or level of formality for unit testing; it leaves the chief programmer to do what's appropriate.

It's acceptable to use XP unit testing techniques in an FDD environment. Where continuous or regular system builds are performed, it certainly makes sense to have a growing set of tests that can be run against a new build. Again, FDD doesn't specify this because technology and resources differ so much between projects. In some circumstances it's very difficult to produce a set of completely isolated, independent tests that run in a reasonable amount of time.


XP leaves tracking to the project managers, encouraging them to minimize the overhead of collecting data and use large, visible wall charts. By contrast, Tracking by Feature in FDD describes a low-overhead, highly accurate means of measuring progress and provides the data to construct a large variety of practical, useful progress charts and graphs.

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