I did a little sniffing on the web to find out what the acronym stands for, exactly. Silly me. I actually expected a cogent, coherent, standards-based answer.
According to webopedia.com and Wikipedia , the acronym variously stands for “System Development Life Cycle” (or “System Design Life Cycle”) in most cases, and “Systems Development Life Cycle” by the DOJ (why lawyers have any say in this, I don’t know).
Note the singular “System” in most uses (Wikipedia has a re-direct to the plural from the singular, so I presume they are considered to be of equal validity for that reference). Most modern, rapid/agile/fast/whatever methodology references I could find (see here , here and here for examples) refer to it in the singular, although that’s certainly not univerally true (hit the link to the last example above for a real quandary). There are a ton of other, software-focused sites that call it, predictably, the “Software Development Life Cycle.”
I couldn’t find the Yourdon book to verify his Delphinic definition of the acronym. OK, actually: I threw up my hands in dismay after so many un-attributed opinions. I will probably never really care whether Yourdon refers to it in the singular or plural. Based upon what I can find, my gut says that “System” is conversationally interchangeable with “Systems” in most general-purpose cases.
In other words, people call it what they want.
Wait! What about “PLC” (Project Life Cycle)? Isn’t that valid, too? I mean, what if there is/are no “System(s)” involved? Or software? Don’t BAs just care about the “Project?”
I think you get my drift. To cut to the chase: There’s no substitute for a good glossary. No matter how many arguments other people are having about terms, if they are defined in your company’s glossary for all to see, then you can do business.
Isn’t that what it’s all about? Correct me if I’m wrong…