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Author: Karl Wiegers

Karl Wiegers is Principal Consultant with Process Impact, a software development consulting and training company in Portland, Oregon. He has a PhD in organic chemistry. Karl is the author of 14 books, including Software Requirements Essentials, Software Requirements, More About Software Requirements, Successful Business Analysis Consulting, Software Development Pearls, The Thoughtless Design of Everyday Things, and a forensic mystery novel titled The Reconstruction. Karl also has written many articles on software development, design, project management, chemistry, military history, and consulting, as well as 18 songs. You can reach him at or

The 6 Most Important Requirements Practices

Authors sometimes make things longer and more complicated than necessary. Some readers might feel that I’ve been guilty of this myself. The third edition of my book Software Requirements, co-authored with Joy Beatty, is about 245,000 words long, nearly 640 pages in a rather small font. Maybe that seems like overkill, but to be fair, the requirements domain is large and complex.

Books like Software Requirements, Mastering the Requirements Process by Suzanne and James Robertson, and the IIBA’s Business Analysis Body of Knowledge describe dozens of valuable techniques for requirements elicitation, analysis, specification, validation, and management. They’re all useful when thoughtfully applied in appropriate situations. But if you don’t have time to wade through these large volumes, you might like this TL;DR version of the six most important requirements practices that every project team should perform. This article is adapted from Software Requirements Essentials: Core Practices for Successful Business Analysis by Karl Wiegers and Candase Hokanson.


Practice #1: Define Business Objectives

Organizations undertake a project to solve a problem, exploit a business opportunity, or create a new market. Defining the project’s business objectives communicates to all participants and other stakeholders why they are working on the project. The organization could hope to achieve both financial and non-financial business objectives with the new product. Try to quantify the business objectives, and make them measurable, with statements like these:

  • Capture a market share of X percent within Y months.
  • Reach a sales volume of X units or revenue of $Y within Z months.
  • Save X dollars per year currently spent on a high-maintenance legacy system.

Using business objectives aligns all of the team’s work and key decisions. Without defined business objectives, you can’t craft a clear product vision statement or establish the scope of either the entire project or any development increment. The team can’t make good decisions about scope changes or proposed functionality unless they know how those changes match up with the business objectives.

Keeping the scope in focus helps the team avoid scope creep while still adapting to changing business realities. And how can you know if the project was a success unless someone defined its business objectives and success criteria up front?


Practice #2: Understand What Users Need to Do with the Product

I strongly advocate taking a usage-centric approach to requirements development and solution design, rather than a feature- or product-centric approach. Understanding the tasks that users need to perform and the goals they want to achieve lets the business analyst (BA) derive the functionality that developers must implement.

When you focus on exploring features rather than user goals, it’s easy to overlook some necessary functionality. It’s also easy to include functionality that seems cool but doesn’t help users get their jobs done. Use cases are an effective technique for maintaining this usage-centric mindset.

Seeking to understand what users need to do with the product implies several other important BA activities, including these:

  • Identifying a wide range of project stakeholders
  • Characterizing distinct user classes that have largely different requirements
  • Identifying individuals to serve as the voice of the customer for each user class (product champions)
  • Selecting appropriate requirements elicitation techniques to engage with users
  • Establishing decision-making processes to resolve conflicts and priorities across user classes
  • Building and evaluating prototypes or early releases to stimulate user feedback




Practice #3: Prioritize the Requirements

I doubt that any project has ever implemented every bit of requested functionality. Even if you could implement it all, you can’t do it all at once. Your goal is to deliver the maximum business value to your customers at the lowest cost and in the shortest time. Achieving this goal demands that you prioritize requirements so the team can work on them in the most appropriate sequence.

Prioritization involves considering how much each proposed requirement contributes to achieving the project’s business objectives. Prioritizing requirements lets the team decide which of the work items remaining in the backlog to defer or omit because of time and resource constraints. There are numerous requirements prioritization techniques available, including these:

  • In or out
  • Pairwise comparison and rank ordering
  • Three-level scale
  • MoSCoW
  • Relative weighting
  • $100 test

Some of these methods take more effort than others, but those methods also help the project manager or product owner make finer-grained choices. Choose any technique that lets the right stakeholders make good business decisions throughout the project to avoid a frantic “rapid descoping phase” late in the game.


Practice #4: Explore Nonfunctional Requirements

People naturally focus on a product’s functionality when discussing requirements, but those are only part of the solution. Nonfunctional requirements contribute heavily to user satisfaction and suitability for use. When speaking of “nonfunctional requirements,” people most commonly think of quality attributes, sometimes called the “-ilities.” These product characteristics include usability, maintainability, security, reliability, and many others. To help designers devise the most appropriate solution, BAs need to discuss nonfunctional requirements as part of requirements elicitation.

Developers generally don’t directly implement requirements that describe safety, reliability, portability, security, or other characteristics. Instead, these attributes serve as the origin of many functional requirements and drive design decisions. Table 1 indicates the likely categories of technical information that different types of quality attributes will generate.


Table 1. Translating quality attributes into technical specifications (from Software Requirements, 3rd Edition)

Another challenge is that it’s not possible to optimize all of the desired quality factors at once. Designers must make trade-off decisions among the various attributes. Therefore, the team needs to determine which ones are most important to customer success and optimize those. Carefully specifying quality attributes lets you build a product that delights its users, beyond merely doing what it’s supposed to.


Practice #5: Review the Requirements

How do you know if your requirements are accurate? How can you tell if they’re clear enough so all the team members know what to do with them and other stakeholders know what to expect in the solution? No matter how you choose to represent requirements knowledge, it is sometimes ambiguous, incomplete, or simply incorrect.

One of the most powerful quality practices available is peer review of requirements. Convene some colleagues to review both textual requirements and diagrams. Different project participants—BAs, designers, developers, testers, users—will find different kinds of problems during these reviews. Requirements reviews pose some particular challenges. Rather than simply inviting people to look over the requirements, provide some training so reviewers know how to participate effectively and can find as many issues as possible.

A related requirements validation practice is to write conceptual tests based on requirements. Testing requirements is something you can do early in each development cycle to reveal many errors before they are cast into code. Requirements and tests are complementary views of the same knowledge. Requirements describe how the product should behave under certain conditions; tests describe how to tell if it’s exhibiting the correct behaviors.


Practice #6: Plan for Requirements Change

No matter how well you understand the problem and how carefully you prepare the requirements, they won’t be perfect, complete, or static. The world changes around us as we work. New users and new ideas appear. Business rules surface and evolve. Projects inevitably grow beyond their originally envisioned scope. Every team must anticipate requirements changes and establish mechanisms for dealing with them without derailing the team’s commitments.

When you know the project outcome is incompletely defined and likely to change a lot, an incremental, agile approach is a good way to cope with it. You plan to build the requirements—and the solution—in a series of small chunks, expecting the direction to change and accepting the uncertainty of what you’ll have at the end and when you’ll have it.


When the likely degree of change is less extreme, plan to accommodate some growth (along with risks, imprecise estimates, and unexpected events) by building contingency buffers into development schedules. Establish a requirements change process so the right people can get the right information to make good business decisions about which proposed changes to incorporate to add value with minimal disruption.

Don’t use the expectation of change as a justification for skimping on requirements thinking, though. Excessive requirements churn often indicates that objectives were unclear or the elicitation approach wasn’t effective.


Neglect These Practices at Your Peril

Of course, there are many other valuable requirements activities besides these six. However, these practices greatly increase your chances of building a solution that achieves the desired business outcomes efficiently and effectively. Applying them doesn’t guarantee success for any BA, product owner, or product manager. But neglecting them likely ensures failure.

Five Requirements Prioritization Methods

When customer expectations are high and timelines are short you need to make sure your project team delivers the most valuable functionality as early as possible.

Prioritization is the only way to deal with competing demands for limited resources. 

Stakeholders on a small project often can agree on requirement priorities informally. Large or contentious projects with many stakeholders demand a more structured approach. You need to removes some of the emotion, politics, and guesswork from the process. This article discusses several techniques teams can use for prioritizing requirements and some traps to watch out for.

Two Big Traps

Be sure to watch out for “decibel prioritization,” in which the loudest voice heard gets top priority, and “threat prioritization,” in which stakeholders holding the most political power always get what they demand. These traps can skew the process away from addressing your true business objectives.

In or Out

The simplest method is for a group of stakeholders to work down a list of requirements and decide for each if it’s in or it’s out. Refer to the project’s business objectives to make this judgment, paring the list down to the bare minimum needed for the first iteration or release. When that iteration is underway, you can go back to the previously “out” requirements and repeat the process for the next cycle. This is a simple approach to managing an agile backlog of user stories, provided the list of pending requirements isn’t too enormous.

Pairwise Comparison and Rank Ordering

People sometimes try to assign a unique priority sequence number to each requirement. Rank ordering a list of requirements involves making pairwise comparisons among all of them so you can judge which member of each pair has higher priority. This becomes unwieldy for more than a few dozen requirements. It could work at the granularity level of features, but not for all the functional requirements for a good-sized system as a whole.

Rank ordering all requirements by priority is overkill, as you won’t be releasing them all individually. You’ll group them together by release or development iteration. Grouping requirements into features, or into small sets of requirements with similar priority or that otherwise must be implemented together, is sufficient.

Three-Level Scale

A common approach groups requirements into three priority categories. No matter how you label them, if you’re using three categories they boil down to high, medium, and low priority. Such prioritization scales usually are subjective and imprecise. To make the scale useful, the stakeholders must agree on what each level in their scale means.

I like to consider the two dimensions of importance and urgency. Every requirement can be considered as being either important to achieving business objectives or not so important, and as being either urgent or not so urgent. This is a relative assessment among a set of requirements, not an absolute binary distinction. These alternatives yield four possible combinations (Figure 1), which you can use to define a priority scale:

* High priority requirements are important because customers need the capability and urgent because they need it in the next release. Alternatively, there might be compelling business reasons to implement a requirement promptly, or contractual or compliance obligations might dictate early release. If a release is shippable without a particular requirement, then it is not high priority per this definition. That’s a hard-and-fast rule.

* Medium priority requirements are important (customers need the capability) but not urgent (they can wait for a later release).

* Low priority requirements are neither important (customers can live without the capability if necessary) nor urgent (customers can wait, perhaps forever).

Watch out for requirements in the fourth quadrant. They appear to be urgent to some stakeholder, perhaps for political reasons, but they really aren’t important to achieving your business objectives. Don’t waste your time implementing these—they don’t add sufficient value to the product. If they aren’t important, either set them to low priority or scrub them entirely.

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Figure 1. Requirements prioritization based on importance and urgency.

On a large project you might want to perform prioritization iteratively. Have the team rate requirements as high, medium, or low priority. If the number of high-priority requirements is excessive and you can’t fit them all into the next release, perform a second-level partitioning of the high-priority ones into three groups. You could call them high, higher, and highest if you like, so people don’t lose sight of the fact that they were originally designated as high.


Those requirements rated “highest” become your new group of top-priority requirements. Then, group the “high” and “higher” requirements in with your original medium-priority group (Figure 2). Taking a hard line on the criterion of “must be in the next release or that release is not shippable” helps keep the team focused on the truly high-priority capabilities.

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Figure 2. Multipass prioritization keeps the focus on a manageable set of top-priority requirements.

Watch for requirement dependencies when prioritizing with the three-level scale. You’ll run into problems if a high-priority requirement depends on another that’s planned for later implementation.


The four capitalized letters in the MoSCoW prioritization scheme stand for four possible priority classifications:

Must: The requirement must be satisfied for the solution to be considered a success.

Should: The requirement is important and should be included in the solution if possible, but it’s not mandatory to success.

Could: It’s a desirable capability, but one that could be deferred or eliminated. Implement it only if time and resources permit.

Won’t: This indicates a requirement that will not be implemented at this time but could be included in a future release.

The MoSCoW scheme changes the three-level scale of high, medium, and low into a four-level scale. It doesn’t offer any rationale for making the decision about how to rate the priority of a given requirement compared to others. MoSCoW is ambiguous as to timing, particularly when it comes to the “Won’t” rating: does it mean “not in the next release” or “not ever?” The three-level scale that considers importance and urgency and focuses specifically on the forthcoming release or iteration.

Agile projects often use the MoSCoW method, but I’m not a big fan of it. Here’s how one consultant described how a client company actually practiced the MoSCoW methods:

All the action centers around getting an “M” for almost every feature or requirement that is captured. If something is not an “M” it will almost certainly not get built. Although the original intent may have been to prioritize, users have long since figured out to never submit something that does not have an “M” associated with it.

Do they understand the nuanced differences between S, C, and W? I have no idea. But they have figured out the implications of these rankings. They treat them all the same and understand their meaning to be “not happening any time soon.”


One way to make prioritization more tangible is to cast it in terms of an actual resource: money. In this case, it’s just play money, but it’s money nonetheless.

Give the prioritization team 100 imaginary dollars to work with. Team members allocate these dollars to “buy” items they’d like to have implemented from the set of candidate requirements. Allocating more dollars weights the higher-priority requirements more heavily. If one requirement is three times as important to a stakeholder as another, she might assign nine dollars to the first requirement and three dollars to the second.

But 100 dollars is all the prioritizers get—when they’re out of money, nothing else can be implemented, at least not in the release they’re currently focusing on. You could have different participants in the prioritization process perform their own dollar allocations, and then add up the total number of dollars assigned to each requirement. That will show which ones collectively come out as having the highest priority.

Watch out for participants who game the process to skew the results. If you really, REALLY want a particular requirement, you might give it all 100 of your dollars to try to float it to the top of the list. In reality, you’d never accept a system that possessed just that single requirement.

Nor does this scheme take into account any concern about the relative amount of effort needed to implement each of those requirements. If you could get three requirements each valued at $10 for the same effort as one valued at $15, you’re likely better off with the three. The scheme is based solely on the perceived value of certain requirements to a particular set of stakeholders, which is a limitation of many prioritization techniques.

It’s Not All Going to Fit

Sometimes customers don’t like to prioritize requirements. They’re afraid they won’t ever get the ones that are low priority. Maybe they won’t. But if you can’t deliver everything, make sure you do deliver those capabilities that are most important to achieving your business objectives. Prioritize to focus the team on delivering maximum value as quickly as possible.


We Don’t Need No Stinkin’ Code: Testing Software Requirements

Someone once asked me when you can begin testing software. “As soon as you’ve written your first requirement, you can begin testing,” I replied.

It’s hard to visualize how a system will function by reading some requirements. Tests that are based on requirements make the expected system behaviors more tangible. Even the simple act of designing tests reveals many requirements problems long before you can execute those tests on a running system.

Requirements and Tests

Tests and requirements present complementary views of the system. Creating multiple views of a system—written requirements, diagrams, tests, prototypes, and so forth—provides a much richer understanding of the system than can any single representation. Some agile development methods emphasize writing user acceptance tests from user stories in lieu of writing detailed functional requirements. Thinking about the system from a testing perspective is valuable, but that approach still leaves you with just a single representation of requirements knowledge, so you must trust it to be correct.

Writing black-box (functional) tests crystallizes your vision of how the system should behave under certain conditions. Vague and ambiguous requirements will jump out at you because you won’t be able to describe the expected system response. When business analysts (BAs), developers, and customers walk through tests together, they’ll codify a shared vision of how the product will work and increase their confidence that the requirements are correct.

A personal experience brought home to me the importance of combining test thinking with requirements specification. I once asked my group’s UNIX scripting guru, Charlie, to build a simple e-mail interface extension for a commercial defect-tracking system we had adopted. I wrote a dozen functional requirements that described how the e-mail interface should work. Charlie was thrilled. He’d written many scripts for people, but he’d never seen written requirements before.

Unfortunately, I waited a couple of weeks before I wrote the tests for this e-mail function. Sure enough, I had made an error in one of the requirements. I found the mistake because my mental image of how I expected the function to work, represented in about twenty tests, was inconsistent with one of the requirement. Chagrined, I corrected the defective requirement before Charlie had completed his implementation, and when he delivered the script, it was defect free. It was a small victory, but small victories add up.

Conceptual Tests

You can begin deriving conceptual tests from user requirements early in the development process. Use the tests to evaluate functional requirements, analysis models, and prototypes. The tests should cover the normal flow of each use case, alternative flows, and the exceptions you identified during elicitation and analysis. Similarly, agile acceptance tests should cover both expected behaviors and exceptions.

Consider an application called the Chemical Tracking System. One use case, “View a Stored Order,” let the user retrieve a particular order for a chemical from the database and view its details. Some conceptual tests are:

  • User enters order number to view, order exists, user placed the order. Expected result: show order details.
  • User enters order number to view, order doesn’t exist. Expected result: Display message “Sorry, I can’t find that order.”
  • User enters order number to view, order exists, user didn’t place the order. Expected result: Display message “Sorry, that’s not your order. You can’t view it.”

Ideally, a BA will write the functional requirements and a tester will write the tests from a common starting point, as shown in Figure 1. Ambiguities in the user requirements and differences of interpretation will lead to inconsistencies between the views represented by the functional requirements, models, and tests. Those inconsistencies reveal errors. As developers translate requirements into user interface and technical designs, testers can elaborate the conceptual tests into detailed test procedures.

no code pic 1Figure 1. Development and testing work products derive from a common source.

A Testing Example

Let’s see how the Chemical Tracking System team tied together requirements specification, analysis modeling, and early test-case generation. Here are some pieces of requirements information, all of which relate to the task of requesting a chemical.

Use Case. A use case is “Request a Chemical.” This use case includes a path that permits the user to request a chemical container that’s already available in the chemical stockroom. Here’s the use case descriptionUse Case. A use case is “Request a Chemical.” This use case includes a path that permits the user to request a chemical container that’s already available in the chemical stockroom. Here’s the use case description.

The Requester specifies the desired chemical to request by entering its name or chemical ID number. The system either offers the Requester a container of the chemical from the chemical stockroom or lets the Requester order one from a vendor.


Functional Requirement. Here’s a bit of functionality associated with this use case:

  1. If the stockroom has containers of the chemical being requested, the system shall display a list of the available containers.⦁ If the stockroom has containers of the chemical being requested, the system shall display a list of the available containers.
  2. The user shall either select one of the displayed containers or ask to place an order for a new container from a vendor.

Dialog Map. Figure 2 illustrates a portion of the dialog map for the “Request a Chemical” use case that pertains to this function. A dialog map is a high-level view of a user interface’s architecture, modeled as a state-transition diagram. The boxes in this dialog map represent user interface displays (dialog boxes in this case), and the arrows represent possible navigation paths from one display to another.

no code pic 2Figure 2. Portion of the dialog map for the “Request a Chemical” use case.Figure 2. Portion of the dialog map for the “Request a Chemical” use case.

Test. Because this use case has several possible execution paths, you can envision numerous tests to address the normal flow, alternative flows, and exceptions. The following is just one test, based on the flow that shows the user the available containers in the chemical stockroom:

At dialog box DB40, enter a valid chemical ID; the chemical stockroom has two containers of this chemical. Dialog box DB50 appears, showing the two containers. Select the second container. DB50 closes and container 2 is added to the bottom of the Current Chemical Request List in dialog box DB70.

Ramesh, the test lead for the Chemical Tracking System, wrote several tests like this one, based on his understanding of how the user might interact with the system to request a chemical. Such abstract tests are independent of implementation details. They don’t describe entering data into specific fields, clicking buttons, or other interaction techniques. As development progresses, the tester can refine these abstract tests into specific test procedures.

Now comes the fun part—testing the requirements. Ramesh first mapped the tests against the functional requirements. He checked to make certain that every test could be “executed” by going through a set of existing requirements. He also made sure that at least one test covered every functional requirement.

Next, Ramesh traced the execution path for every test on the dialog map with a highlighter pen. The yellow line in Figure 3 shows how the preceding test traces onto the dialog map.

no code pic 3Figure 3. Tracing a test onto the dialog map for the “Request a Chemical” use case.

By tracing the execution path for each test on the model, you can find incorrect or missing requirements, improve the user’s navigation options, and refine the tests. Suppose that after “executing” all the tests in this fashion, the navigation line in Figure 2 labeled “order new container” that goes from DB50 to DB60 hasn’t been highlighted. There are two possible interpretations:

  • That navigation isn’t a permitted system behavior. The BA needs to remove that arrow from the dialog map. If you have a requirement that specifies the transition, that requirement also needs to go.
  • The navigation is a legitimate system behavior, but the test that demonstrates the behavior is missing.

When I find such a disconnect, I don’t know which possible interpretation is correct. However, I do know that all of the views of the requirements—textual, models, and tests—must agree, so there’s clearly something wrong.

Suppose that another test states that the user can take some action to move directly from DB40 to DB70. However, the dialog map doesn’t contain such a navigation line, so the test can’t be “executed:” you can’t get there from here. Again, there are two possible interpretations:

  • The navigation from DB40 to DB70 is not a permitted system behavior, so the test is wrong.
  • The navigation from DB40 to DB70 is a legitimate function, but the requirement that allows you to execute the test is missing.

In these examples, the BA and the tester combined requirements, analysis models, and tests to detect missing, erroneous, or unnecessary requirements long before any code was written. Every time I use this technique, I find errors in all the items I’m comparing to each other, quickly and cheaply

As consultant Ross Collard  pointed out, “Use cases and tests work well together in two ways: If the use cases for a system are complete, accurate, and clear, the process of deriving the tests is straightforward. And if the use cases are not in good shape, the attempt to derive tests will help to debug the use cases.” I couldn’t agree more. Conceptual testing of software requirements is a powerful technique for discovering requirement ambiguities and errors early on.

Karl Wiegers is Principal Consultant at Process Impact. He’s the author of numerous books and articles on software development, project management, design, quality, chemistry, military history, and other topics. This article is adapted from Software Requirements, 3rd Edition by Karl Wiegers and Joy Beatty. Karl’s latest book is The Thoughtless Design of Everyday Things.

Using Feature Trees to Depict Scope

A feature consists of one or more logically related system capabilities that provide value to a user and are described by a set of functional requirements. Many business analysts use features as a way to describe the scope of a project. However, a simple list doesn’t readily show the size and complexity of various features. Nor does quickly skimming a feature list easily reveal the full scope of a project. A feature tree is a visual analysis model that organizes a set of features in a format that makes them easy to understand.

Feature Tree Format

The structure of feature trees is based on fishbone diagrams or Ishikawa diagrams, which are commonly used to organize information into logical groupings based on relationships. Fishbone diagrams are typically used to model cause-and-effect relationships, but feature trees use the same format to organize the planned features of a software solution.

A feature tree can show up to three levels of features, commonly called level 1 (L1), level 2 (L2), and level 3 (L3). L2 features are subfeatures of L1 features, and L3 features are subfeatures of L2 features. Below L3 lie individual requirements, which aren’t shown on the feature tree. A feature tree does not necessarily need to have three levels of features; if the solution and features are simple, there might be just L1 features and their more detailed functional requirements.
As Figure 1 illustrates, the basic building block of the model is a feature with a single line. The feature names are simply shown as words on the tree, and the lines link related features together. Feature names should be concise, typically just two or three words.

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Figure 1- Feature tree grouping

Each feature is shown on its own line. Each subfeature also has its own line, which branches off the parent feature’s line. In Figure 1, the L1 feature has been decomposed into four subfeatures at the L2 level. The order in which the subfeatures are attached to the line is not important, as long as common subfeatures branch off the same parent feature line. The L1 features can be shown in boxes, to highlight those elements on the tree as being the main features under which subfeatures fall. This enables anyone who skims the model to understand the big picture of the scope of the solution.

A Sample Feature Tree

Figure 2 shows a partial feature tree for a chemical-tracking information system. Note that the main branch or “trunk” of the tree is a straight line with an oval at the end that shows the name of the product being developed. The shaded boxes represent the L1 features, such as Order Chemicals and Inventory Management. Each such feature represents a block of logically related functions that a user might want to perform. The lines coming off an L1 branch are the L2 features: Search and Chemical Request are subfeatures of Order Chemicals. The branches off an L2 branch are the L3 features: Local Lab Search and Catalog Search are subfeatures of Search.

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Figure 2 – Partial feature tree for the Chemical Tracking System

Using the Feature Tree

A feature tree is typically created early in a project to define the breadth of work that will be completed, but it is useful throughout the project to communicate changing scope and to help the team members organize and coordinate their work. A feature tree can be included in the project’s vision and scope document or project charter, or it can be stored elsewhere and referenced as needed. A key purpose of visual models like the feature tree is to foster clear and accurate communication among the project stakeholders. That clarity is more important than dogmatically adhering to the rules for a “correct” diagram.

Release Planning

Feature trees can be used during release planning to decide and show which features are allocated to each release or development increment. A feature could be implemented in its entirety in a specific release, or only a portion could be implemented by choosing just certain L2 and L3 subfeatures. Future releases could enrich these rudimentary implementations by adding more L2 and L3 subfeatures until each feature is fully implemented in the final product. The scope of a particular release thus consists of a defined set of L1, L2, and/or L3 features chosen from the feature tree. A feature tree can illustrate these feature allocations across releases by using colors or font variations. For example, in Figure 2, the blue features might represent the first release, the red features are the second release, and the black features are yet to be allocated to a release.

Functional Decomposition

Feature trees show all of the planned product features at once, giving a quick view of the solution’s breadth of functionality. Organizing the features in this fashion makes it easy to identify missing and unnecessary features. The feature tree provides a functional decomposition of the solution for use throughout all phases of the project, including organization of the requirements, planning the work around the requirements, and bounding of the scope of work. Feature trees provide a much richer view of features than a simple list can show.

Find Gaps

Because there is no way to guarantee that a feature tree is complete, have your stakeholders review it to make sure it reflects their expectations. The earlier that gaps are identified the better, because finding them late in a project can derail the project (and traumatize the participants). Update the feature tree any time scope is changed to reflect the final planned feature set.

Depict Project Scope

The feature tree should be used to set and communicate the scope of the project. It is a useful model to circulate among executives and lead stakeholders to quickly communicate the scope of the solution. Because you can fit so many features on one page, the feature tree is a good choice when you need a diagram that anyone can look at to understand the gist of the solution quickly. For packaged software, a feature tree provides the features that go in a short bullet list or description of the product’s functionality.

When a stakeholder joins a project midstream it can be a challenge for him to get a high-level picture of what an existing system does or what a new system is supposed to do. Feature trees allow all team members to understand and agree on the capabilities of the solution at a high level. They show the breadth of the solution scope at a consistent level of depth.

Organize the Requirements

The divisions in a feature tree provide a convenient way to organize requirements in deliverables so that the information is grouped by feature. In a requirement deliverable, all of the requirements for each L1 feature and its subfeatures can be grouped together. For the example discussed earlier, there could be a full set of models and requirements for Inventory Management and another for Health and Safety.

If your team is frustrated by the limitations of text-only requirements documentation, consider using feature trees to provide an at-a-glance visual representation of project scope.

Don’t forget to leave your comments below.

About the Writers:

Karl Wiegers is Principal Consultant at Process Impact, Joy Beatty is a Vice President at Seilevel, Karl and Joy are co-authors of the recent award-winning book Software Requirements, 3rd Edition (Microsoft Press, 2013), from which this article is adapted.

Specifying Requirements for Outsourced Projects

Rather than building systems in house, many organizations outsource development to contract development companies. They might outsource the work to take advantage of skills they do not have available in-house, to augment their internal staff, or in an attempt to save money or time. The outsourced development supplier could be located physically nearby, on the other side of the world, or anywhere in between.

The role of a business analyst is even more important on these projects than on a co-located project. If the team members are all in one location, developers can walk down the hall to ask the BA a question or to demonstrate newly developed functionality. This close collaboration can’t happen in the same way with outsourced development. Compared to in-house development, outsourced—and particularly offshore—projects face requirements-related challenges such as the following:

  • It’s harder to get developer input on requirements and to pass along user feedback to developers.
  • A formal contractual definition of requirements is necessary, which can lead to contention if differences of interpretation are discovered late in the project
  • There might be a bigger gap between what the customers ultimately need and the product they get based on the initial requirements, because there are fewer opportunities to adjust the project’s direction along the way.
  • It can take longer to resolve requirements issues because of large time zone differences.
  • Communicating the requirements is more difficult because of language and cultural barriers.
  • Limited written requirements that might be adequate for in-house projects are insufficient for outsourced projects, because users and BAs are not readily available to answer developer questions, clarify ambiguities, and close gaps.

This article suggests some techniques for successful requirements development and management on outsourced projects.

Appropriate Requirements Precision

Outsourcing product development demands high-quality written requirements, because your direct interactions with the development team are likely to be minimal. As shown in Figure 1, you’ll be sending the supplier a request for proposal (RFP), a set of requirements, and product acceptance criteria. Both parties will engage in a review and will reach agreement, perhaps with negotiation and adjustments, before the supplier initiates development. The supplier will deliver the finished software product and supporting documentation.

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Figure 1. Requirements are the cornerstone of an outsourced project.

With outsourcing, you won’t have the same opportunities for day-to-day clarifications, decision making, and changes that you enjoy when developers and customers work in close proximity. Particularly with offshore development, you should anticipate that the supplier will build exactly what you ask them to build. You will get no more and (hopefully!) no less, sometimes with no questions asked. The supplier likely won’t implement the implicit and assumed requirements you thought were too obvious to write down. Poorly defined and managed requirements are a common cause of outsourced project failure.

As with in-house development, visual requirements models augment functional and nonfunctional requirements for outsourced teams. Using visual models to supplement written specifications is even more valuable if you are working across cultures and native languages, because it gives developers something to check their interpretations against. However, be sure the developers can understand the models you send them and interpret them accurately.

Prototypes can also help clarify expectations for the supplier team. Similarly, the supplier can create prototypes to demonstrate to the acquirer their interpretation of the requirements and how they plan to respond to them. This is a way to create more customer-development interaction points to make course adjustments early in the project rather than late.

Watch out for the ambiguous terms found in Chapter 11 of Software Requirements, 3rd Edition that cause so much confusion. I once read a requirements specification intended for outsourcing that contained the word “support” in many places. The BA who wrote the requirements acknowledged that the contractor who was going to implement the software wouldn’t know just what “support” meant in each case. A glossary is valuable when dealing with people who don’t share the tacit knowledge held by those who are familiar with the acquiring company’s environment.

Acquirer-Supplier Interactions

Without real-time, face-to-face communication you need other mechanisms to stay on top of what the supplier is doing, so arrange formal touch points between the acquirer and the supplier. Plan time for multiple review cycles of the requirements. Use collaboration tools to facilitate peer reviews with participants in multiple locations. Incremental development permits early course corrections when a misunderstanding sends the supplier’s developers in the wrong direction. If the supplier raises questions, document them and integrate the answers into the requirements. Use an issue-tracking tool to which both supplier and acquirer teams have access.

Outsourced projects often involve teams with disparate company cultures and attitudes. Some suppliers are so eager to please that they agree to outcomes they cannot deliver. When an error is brought to their attention, they might strive to save face by not fully accepting responsibility for the problems. Some developers might hesitate to ask for help or clarification, or to say “I don’t understand.” Employ elicitation and facilitation techniques such as reading between the lines for what isn’t said and asking open-ended questions. Establish ground rules with all team members regarding how they should interact when they work together.

Developers whose first language is different than the language in which the requirements are written might not pick up nuances or fully appreciate the implications of certain statements. They might make user interface design choices that you wouldn’t expect. Things as diverse as date formats, systems of measurement, the symbolism of colors, and the order of people’s given and family names vary between countries. The requirements should avoid the use of colloquialisms, jargon, idioms, and references to pop culture that could be misconstrued.

Change Management

At the beginning of the project, establish a change control process that all participants can use. Using a common set of web-based tools for handling change requests and tracking open issues is essential. Identify the decision makers for proposed changes and the communication mechanisms you’ll use to keep the right people informed. The outsourced development contract should specify who will pay for various kinds of changes, such as newly requested functionality or corrections made in the original requirements, and the process for incorporating the changes into the product.

Acceptance Criteria

Define in advance how you’ll assess whether the contracted product is acceptable to you and your customers. How will you judge whether to make the final payment to the supplier? If the acceptance criteria are not fully satisfied, who’s responsible for making corrections, and who pays for those? Include acceptance criteria in the RFP so the supplier knows your expectations up front. Validate the requirements before you give them to the outsourced team, to help ensure that the delivered product will be on target.

Properly handled, outsourcing the development work can be an effective strategy to build your software system. An essential starting point for a successful outsourcing experience is a set of high-quality, complete, and explicitly clear requirements. If the requirements you provide to the supplier are incomplete or misunderstood, failure is probably at least as much your fault as theirs.

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About the Writers:

Karl Wiegers is Principal Consultant at Process Impact, Joy Beatty is a Vice President at Seilevel, Karl and Joy are co-authors of the recent award-winning book Software Requirements, 3rd Edition (Microsoft Press, 2013), from which this article is adapted.