What Are Requirements?
For purposes of this class, we will focus on what the end user needs or
expects the system to do. These needs and expectations are documented
as requirements for the system. They fall into two general categories:
user requirements (sometimes referred to as functional requirements) and
system performance requirements (sometimes referred to non‐functional
1. User Requirements describe the tasks the user needs the system to
perform, such as:
• What data the system is expected to collect.
• What the system is expected to do with the data that is input.
• What the system is expected to provide as output (reports, results,
Some example user requirements for an online shopping site might be:
• The system must calculate the total of all items in the online or
website shopping cart.
• The system must display to the user similar items that the online
shopper may be interested in.
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• The system must require the user to provide a shipping address.
• The system must automatically fill in the State portion of the
shipping address based on the zip code entered by the user.
• The system must provide the user with a report of all purchases
made via the website.
2. System Performance Requirements are sometimes referred to
as system quality attributes, since they define how the system is
designed, how it will perform when used, and what the user experience
will be (Microsoft, 2009).
They describe how the system will perform, or its quality, in areas such as:
• Usability—The ability for new users to quickly adapt to the software,
including how easy the system is to use and how help is provided for
• Scalability—The ability of the system to accommodate additional
users and/or additional records/transactions
• Availability—The amount or periods of time the system is to be
operational and useable
• Reliability—The ability of the system to create and maintain the data
• Maintainability—The ability of the system to be easily maintained,
corrected and updated
• Performance—The ability of the system to meet time or volume
requirements (respond to user inquiry, update a database, or handle
• Portability—The ability of the system to run/operate on a variety of
end‐user devices or with multiple operating systems
• Interoperability—The ability of the system to interact with other
existing or legacy systems
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System performance requirements also describe security requirements for
the system and data, such as:
• Protection of the system from malicious or accidental actions
• Protection of data as it is transmitted and when it is stored
• User authentication; prevention of unauthorized access
• Authorization of users to perform specific functions; prevention of
unauthorized changes to data
• Data backup and recovery
Some examples of system performance requirements are:
• The system must encrypt the user's payment information when it is
• The system must require a retinal scan for login purposes.
• The system must be capable of handling 5,000,000 transactions per
• The system must operate using Motorola handheld scanners.
• The system must be able to accept financial data directly from the
company’s financial system.
To differentiate between user and system performance requirements, the
business analyst determines whether each requirement describes a task
that the system must perform (user requirement) or describes system
quality or security (system performance requirement).
How Are the Requirements Used?
Requirements can be used to develop a system from scratch, in which
case many detailed requirements for every step of every process need to
be clearly laid out. For example, if an accounting system is to be
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developed, the developers will need to incorporate all the financial and
legal aspects of the process. They will need to know exactly how each
accounting function is to be performed in order to program the system to
carry out the function.
However, if the intent is to acquire a commercial off‐the‐shelf (COTS)
accounting system or to use a software‐as‐a‐service (SaaS) system, then
the requirements may be stated at a much higher level, such as: "the
system must implement the Generally Accepted Accounting Principles
(GAAP)" or "the system must produce a monthly expense statement." In
these cases, the end user is not so concerned about each step in
performing those functions, as long as the system provides them.
Once the requirements are listed, they can be used to:
• Develop a system and test it to be sure it meets the requirements
• Identify one or more COTS or SaaS systems that appear to meet the
• Test the COTS or SaaS systems to determine which one meets the
most requirements and select one for use
• Identify requirements that are not met that may need be added to
the system or may require a separate or additional system(s) or
processes to be implemented
According to Mitre (2018) requirements "can be tested, verified, and/or
validated, and are unique, complete, unambiguous, consistent, and
obtainable, and [can be traced] to original business and mission needs."
Documented requirements can be traced through an entire system
development and implementation process. For example:
• They form the need for a system and define its scope (all the
functions that are to be included).
• They form the basis for estimating the time and cost of developing or
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acquiring the system.
• They are used to develop the system.
• They are used to negotiate any requirements changes that are
proposed by helping to determine how significant the change is.
• They are used to develop test cases to test the system to see if it
functions as needed.
• They are used when modifications or enhancements are proposed to
ensure that the new change does not unintentionally replace
previous functionality, and that the new requirement fits within the
scope of the system's overall functionality.
• They are used to test a modified system to ensure all previous
functions, as well as the new functions, perform as needed.
Microsoft. (2009). Microsoft application architecture guide, 2009.
Retrieved from https://docs.microsoft.com/en‐us/previous‐versions/msp‐
Mitre. (2018). Systems Engineering Guide—Analyzing and Defining
Requirements. Retrieved from https://www.mitre.org/publications
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