Home > Articles > Software Development & Management

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

Product Constraints

Product constraints, in the information technology world, refer to the "ilities."13 To provide an example of different product constraints, the following six "ilities" are discussed in more detail below.

  • Adaptability
  • Reliability
  • Scalability
  • Security
  • Usability
  • Maintainability

The proceeding examples are crucial to the success of the Internet application.

Adaptability Requirements

One business model that is evolving is sometimes referred to as the "choiceboard." This is where the consumer, through the Internet, clicks on the features and prices of what he or she wishes to purchase. The manufacturer provides an online configurator that allows the consumer to select what options he or she is willing to buy and at what price. This new business model requires additional requirements that extend beyond software. This change also affects both the sales and manufacturing processes for the company.

Hence, the Internet application involves changes in the normal business process. In order for the product to succeed, changes in other business areas, or business communities, are required. The community represents the other business units that are impacted by the Internet application.

These changes may not be known when the Internet-based application is being designed for its first iteration. The application must, therefore, be adaptable, meaning that the application must continually change to meet the demands of the customer and the market. It is important to document this requirement to remind the project development team during design reviews of what will occur with each iteration of the product.

Reliability Requirements

Reliability refers to the expectations of the users as to the continual availability of the Internet application (including performance and fault tolerance requirements). Users expect applications to be available on a 24-hour-per-day basis. Reliability requirements speak to the mean time between failures. The Internet application runs on equipment that the users expect to have a minimal mean time between failures. This may require backups in hardware and networks. These, combined with the location requirements, provide valuable input to the network engineers when designing the network infrastructure.

Reliability needs may vary by function and location, so it is important to build a table that correlates the reliability by either "when" or "how" requirements. Tables 3.6 and 3.7 illustrate a means by which specific reliability and performance requirements can be captured and organized. It is important to identify a pattern as to what functions really require high availability and when. With a stock-trading application, for example, the day that stock options become due, volumes are highest. If this is for a specific type of stock, say, an energy stock, the prior clientele may likely reside in Texas. To guarantee reliability for that location on their biggest trading day, equipment may be diverted to support the one-day peak instead of having excess capacity for the entire year. In any case, the requirements need to be explicit so those in charge of planning the capacity for hardware and networks have sufficient knowledge of the users' expectations.

Table 3.6 Reliability (Mean Time Between Failures, MTBF) Requirements

Table 3.7 Reliability (Performance) Requirements

ity for that location on their biggest trading day, equipment may be diverted to support the one-day peak instead of having excess capacity for the entire year. In any case, the requirements need to be explicit so those in charge of planning the capacity for hardware and networks have sufficient knowledge of the users' expectations.

Scalability Requirements

A good example of the importance of scalability was recently depicted in an advertisement in which a small group of entrepreneurially spirited individuals are standing around a personal computer. They are watching the opening of their new business venture, holding their breath as they eagerly await the first customer's order. Elated screams of success grow as the customer orders grow beyond their dreams. Then, quickly, the happiness turns to panic as the orders keep growing and growing. How are they going to satisfy what is now an unanticipated order volume?

This commercial illustrates the need for scalability on two fronts: technology and business community. Technology is the infrastructure that supports the Internet application. Business community is the business infrastructure that supports the product claims.

First, the technology. The technology must be scalable to adapt to the growth of the Internet application without the continual need to throw everything away and start over, the cost of which would deplete any revenue gain. Scalability is building an infrastructure that supports both vertical growth (increase in the number of sales for a specific product) as well as horizontal growth (increase in breadth of product).

It is important to anticipate some growth. Growth will impact the performance of the Internet application. The infrastructure must be flexible enough to support growth in network size, transaction handling, data throughput, page load timings, and security. This requires sophisticated tools that can model capacity planning on the site and network.

With regard to scalability technology requirements, it is important to document the potential growth in increments. A spreadsheet (see Table 3.8) or some CASE tools can be used to document these associative requirement details.

Table 3.8 Capacity Requirements Spreadsheet

What is important is to determine the minimum, average, and maximum number of occurrences for each requirement. In other words, it is important to determine the anticipated volume of events (when), the number of transactions (how), and the number of users (by each type/actor). You also need to capture the timeframe for these volumes. For example, some time-initiated events may be dormant except when the time is triggered (close of the stock exchange or the end of the business day for that country). It is important for the network engineers to model the performance under the worst-case scenarios.

Growth will also impact the business infrastructure that is put in place. It is important to anticipate the risk of a supplier not being able to meet the growth of your business. Some small companies went out of business when UPS went on strike! eCost took a beating when 3Com could not get the chips for Palm Pilots. Scalability, in a business sense, requires risk analysis of all dependent business partners.

B2B supply-chain applications involve multiple vendors using multiple vendors. Scalability business requirements need to anticipate the possibility of a supplier not being able to meet the necessary volumes. In most cases, you can split the anticipated volume across multiple vendors. The business has minimal control over what vendors your vendors use. The scalability business requirements must contain scenarios of supply-chain interruption.

First, identify the possible breaks in the supply chain. Anticipate the worst scenario as well as the probable scenario. Table 3.8 can be adjusted to determine the severity of each possible outage.

At the scope level, scalability will be defined as the need to implement a flexible infrastructure to support the projected growth. At this point, the requirement is still ambiguous; all the volumetrics will most likely not be known. This requirement evolves as more requirements are captured. It is still important to document the scalability need at this point as a reminder that more information is required.

At the planner level, volumetrics begin to emerge. The business units should be able to provide projected numbers of the customers, orders, transactions, and so forth. These volumetrics should be applied to all models. Relationships among functional requirements are also being formed at the business level. As part of defining the relationships, the business unit should be able to project volumetrics about the relationships. For example:

  1. Each potential client will search for five product descriptions, including price and availability, at one time.

  2. One out of three searching clients will, on average, order two products with each order placed.

  3. One out of five customers will bypass the search and place an order for one item.

  4. The bulk of orders are placed between 10 a.m. and 1 p.m. EST on Mondays. The exception is the seven weeks before the end of the calendar year. During that time, the peak period expands to all weekdays.

Large companies that are dabbling in the Internet must not take these volume estimates lightly. There is a possibility that the Internet-based product may outperform the corporation's standard business, making the Internet the leading business unit.

Security Requirements

All of these business processes and information require some level of security processing. One type of security is required to protect the client, another to protect the corporation. The requirements engineer must spend time with all requirement suppliers on the impact of poor security. Security requirements must be captured on two fronts: (1) to protect the Internet user from intruders, and (2) to protect the corporation from theft or corruption (viruses).

It is critical to answer the simple question of what would be the impact to the corporation or the customer if data or processing were lost due to a security breach. If possible, attempt to obtain a quantifiable number at the following levels:

  • Five-minute outage
  • Day-long outage
  • Week-long outage

Then try to determine through awareness-type questioning whether the data would actually be lost or corrupted. Sample scenarios include

  • If data became corrupted
  • If a competitor obtained any data
  • If any file (data, voice, media) became corrupted

Clients must feel comfortable doing business with you. They must feel that you are reputable and that the payment process is a private transaction used for this purchase alone.

There are thieves among us. The first one who comes to mind is the predator who tries to destroy or capture corporate information.14 The other type of thief is one who wants to steal the product or service. When a thief of this sort obtains confidential information by using stolen payment options, it can cripple a company. Security must be taken very seriously and viewed as having a potentially negative impact at any level.

The seven worst security mistakes that senior executives make15 include four that can be documented during the requirements process:

  1. Pretending the problem will go away if they ignore it

  2. Relying primarily on a firewall

  3. Failing to understand the relationship of information security to the business problem (understanding physical security but not seeing the consequences of poor information security)

  4. Failing to realize how much money their information and organizational reputations are worth

It is up to the requirements engineer to capture security requirements and associate the need to "who," "what," "how," and "where" as well as any interactions between these functional focus areas.

Usability Requirements

The Internet has evolved current business models to a point where the consumer holds the power. This has changed—and will continue to change—the way companies relate to their customers and compete with one another. Usability is a product constraint that directly speaks to the customer's ability to use the Internet product, and it must be captured. It should include

  • The maximum allowed response time

  • The availability to access 24 hours a day, seven days per week

  • The ability to customize views at specific points

  • The ability to filter information, minimizing what the user would perceive as "clutter data"

  • The availability of choices for the product

Most importantly, a consideration for usability is how many clicks it takes to retrieve information and how many clicks to complete a workflow. Response time can be eaten away with every screen of updated or new information. This translates to time that the user is not willing to give up if he perceives that the usability of the application is at fault. The requirements engineer should capture this type of need and associate the information with each "how" requirement, similar to how you related scalability requirements. This assists the designers (users of these requirements) in developing an effective product with an emphasis on usability.

Maintainability Requirements

Every one to three months (sometimes sooner), new features are offered in new product iterations. Many of these iterations are developed in parallel with each other. The work products, from the requirements to the code, must be easily maintained in order to keep to this rigorous schedule. Conforming to standards defined by the organization (and by international standards organizations) facilitates the making of products that are easily updated and maintained through each iteration. A general maintainability requirement must be defined at the owner level. As the relationships to other nonfunctional and functional focus areas are defined, the maintainability should be clarified as to its specific impact on the work products produced in those other focus areas. As the other requirements evolve, so should the maintainability requirement by describing the detail requirements as they relate to the structure and standard for the different perspectives and focus work products.

  • + 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.


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