Issue: September/October 2000 | PDF
What’s In a Name?
One consequence of the youthfulness of software engineering is that we have not standardized our terminology. This might seem like a small matter of primarily academic interest, but the lack of defined terms has significant and unexpected consequences. The number of ambiguous terms in software engineering is practically limitless, and in this column I will focus on only a few: “requirements,” “prototype,” “specification,” “architecture,” and “analysis.”
Problems with terminology begin as soon as a project gets underway. Suppose your customer asks you to write a “requirements” document. What do you write? I have found that different organizations might call any of the following a “requirements document”:
- Half-page software product vision
- Two page list of key features
- 50 page list of detailed end-user-level requirements
- 250 page exhaustive listing of every visual element on every screen, input-field-by-input-field descriptions of all possible input conditions, all possible system state changes, detailed description of every persistent data element, and so on
For my purposes, I have gravitated toward calling Level 1 requirements a “product vision,” Level 2 a “feature list,” Level 3 a “functional requirements document,” and Level 4 a “functional specification,” but my usage is by no means standard.
One technique used to pin down requirements is prototyping, which brings on a second wave of confusing terminology. Some people use “prototype” to refer to a functioning program that will be evolved into a working program but which is less robust than the fully functional program will be (“evolutionary prototype”). Other people use it to refer to a non-functional mock-up that will be used to illustrate how the fully functional system will look or operate, but which is not, itself, intended to be evolved into the working system (“throwaway prototype”). Still others use the term “prototype” to refer to low-quality software that is at an early pre-release stage of development.
At some point, most project teams create a “specification” or “spec,” which muddies the waters still further. “Specification” seems to refer most commonly to detailed functional requirements—screen by screen descriptions of all visual elements, input-field-by-input-field descriptions of all possible input conditions and system responses, and so on (my level 4 requirements, above). Almost as often, “spec” refers to what I have called Level 2 or Level 3 requirements. Some people use “spec” to refer to an architecture document, detailed design, or other work product. One company used the word “specification” to refer to a document that contained every piece of information relevant to a project—and the document didn’t have any requirements information at all.1
“Architecture” has varying meanings, too. Some people use “architecture” to refer to the design of the user interface, especially to the flow among the different elements of the user interface that will be visible to the software’s users, but not to technical implementation work. Others use “architecture” to mean partitioning a system into subsystems and defining the interfaces between them. Still others mean anything related to the functional design of the software—to technical implementation work.
Finally, the meaning of the word “analysis” varies from one organization to the next. Many use it to refer to an early-requirements activity of analyzing user needs. Others use it interchangeably with requirements elicitation and documentation—essentially synonymous with “requirements engineering.” Others use “analysis” to refer to the activities that bridge requirements gathering to design work. Once again, no meaning is common enough to allow any single meaning to be declared an obvious standard.
What’s in a Name?
These differences in the ways common software engineering terms are used can have major consequences. I participated as an expert witness in a multi-million-dollar lawsuit in which a company sued its former Vice President of Technology for non-performance of work duties. The company alleged that it had assigned the VP to develop a prototype and architecture, and that he had failed to do so. The VP was flabbergasted that the company could baldly assert that he had not created these work products when in fact the work products were available for all to see.
It turned out that the VP had developed an evolutionary user interface prototype and demonstrated it to the company’s senior management. Senior management was enthusiastic about the prototype and encouraged the VP to “finish” the prototype. Senior management’s assumption was that the prototype was a throwaway prototype, and remaining details could be added quickly as a precursor to the main implementation effort. The VP’s assumption was the “finishing the prototype” meant evolving the prototype to a level of robustness and reliability at which it could be released for commercial use. “Finishing the prototype” meant “finishing the product.” This lead to a critical miscommunication in which senior management thought the prototyping work could be finished in a matter of days or at most weeks, while the VP thought the prototype development would take many months, possibly as long as a year.
At issue in the same lawsuit, senior management had assigned the VP of Technology to create a “product architecture.” The VP’s prototype showed many details of the user interface design, flow among user interface elements, and so on. He considered this to be a full-fledged product architecture. The company’s senior management expected the VP to develop a functional architecture that defined the software’s decomposition into subsystems, class hierarchies, network architecture, and so on. As the company insisted that the VP work harder on the “architecture,” the VP spent more time fleshing out details of the prototype. The more time the VP spent fleshing out the prototype, the more frustrated the senior management became that the prototype was taking so much longer than they expected, and the more frustrated they were that the VP refused to create an architecture.
Coming to Terms
Not every misunderstanding of software engineering terms ends up in court, but we as a profession face some serious implications of these undefined terms. The IEEE Computer Society is currently creating a test that will be used to award “Certified Software Engineering Professional” credentials. It’s challenging to develop a multiple choice question like “What should go into a requirements document” (or architecture, prototype, spec, or analysis) when common usage varies so much.
The legal field has a useful notion called a “term of art.” To lawyers, a term of art is a word that has been analyzed and discussed so much in court cases and statutes that the word has a precisely defined meaning, a meaning that may be quite different than the common language meaning. Software engineering has taken a step in the right direction with IEEE Std 610.12, “IEEE Standard Glossary of Software Engineering Terminology.” I hope that as the years pass, common usage of these critical terms will gravitate to specific, precise meanings, and that IEEE Std 610.12 and common usage will be brought into alignment.
1. Thanks for Karl Wiegers for this example.
The closest we have to a vocabulary standard are the terms defined in IEEE Std 610.12. Here are the IEEE standard definitions of the terms used in this column:
Architecture. The organizational structure of a system or component.
Prototype. A preliminary type, form, or instance of a system that serves as a model for later stages or for the final, complete version of the system.
Requirement. (1) A condition or capability needed by a user to solve a problem or achieve an objective. (2) A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed documents. (3) A documented representation of a condition or capability as in (1) or (2).
Requirements Analysis. (1) The process of studying user needs to arrive at a definition of system, hardware, or software requirements. (2) The process of studying and refining system, hardware, or software requirements.
Specification. A document that specifies, in a complete, precise, verifiable manner, the requirements, design, behavior, or other characteristics of a system or component, and, often, the procedures for determining whether these provisions have been satisfied.