"how to use SHALL or MUST"

[pardal]

How it is interpreted or understanding the mean of
SHALL or MUST in specification.

Which one is a mandatory and which is optional.



Pardal

 

[IRstuff]

No confusion.

No one here would argue that a requirements specfication is remotely an example of normal English literature.

TTFN

 

[jsummerfield]

KimBellingrath recommends using the active voice instead of the passive voice. Write the specification using commands.
Consider, Provide, Furnish, Install, Clean, Submit, Weld, Ship, Design, Calculate, ... Combine to clarify the scope. Furnish and install. Avoid "by others" if you can identify the others. As Kim said, "Do it" instead of "it shall be done".

After writing the specification search for any use of passive words such as shall, must, have, ... At first, use the grammer check software with passive voice rule turned on to help you get the style.

For practice, edit examples of government regulations that are almost exclusively passive voice. With practice you can enjoy this newly found language.

John

 

[IRstuff]

Kim's examples are work instructions, which are appropriate for assembly and fab drawings, since it's a communication between the engineer and the fabricator.

A "specification" is a set of requirements that are to be adhered to by the design, so it's somewhat odd to say, "Communicate to the outside world using TCP/IP." as there is no one on the other side of this imperative execute this command.

Specification drawings detail inherent properties of the item, such as performance, weight, etc. You don't tell your laptop, "Weigh no more than 10 pounds." However, "Laptop shall weigh no more than 10 pounds," makes sense as a requirement.

Moreover, defense specification drawings must adhere to MIL-STD-961, which mandates the use of "shall" to express a binding requirement.

TTFN

 

[jsummerfield]

We issue specifications for equipment, services, etc. Let’s say that this is a specification submitted to various suppliers to bid on your laptop computer. It is perfectly acceptable to specify a communication interface such as “Furnish the computer with at least two 100baseT Ethernet communications ports for an interface to widgets using TCP/IP." This is a clear requirement. If the computer has three Ethernet ports it is OK provided that at least two are 100baseT. Further, perhaps you have to carry the computer up three flights of stairs each morning. You could passively write “The weight of the computers shall not exceed 5 kg (11 pound).” Furnish computers weighing 5 kg (11 pound) or less. Each make sense as a requirement. If the computers proposed weigh 6 kg they are not fully compliant with the specification.

John

 

[IRstuff]

What you are describing is a statement of work, not a design specification. "Furnish" is an imperative that requires an action, hence is a statement of work to be accomplished. It implies that the subject can design OR procure to meet the requirement. This is typical of procurement contracts not specifications.

MIL-STD-961 covers specifically what are called Prime Item Development Specifications, which are DESIGN requirements, otherwise, a totally different agency would be responsible for procurement. While sloppy language allows for "Design computer to weigh less than 10 pounds," when you have >300 such requirements all starting with "Design computer" it becomes pointless to have an active voice.




TTFN

 

[procadman2]

MIL-STD-961 is another example of Military versus the real technical world.

I have a manual written by someone who assumes he understands 961.

Instead of listing required steps in a standard fashion, ie: 2.1 2.1a 2.2 etc., the author begins each requirement with "shall". This goes on for over 20 steps. This is not what 961 is stating to do.

Using "shall" and "must" in most cases draws the readers attention away from the rest of the requirements. All of the requirements must be met. Some are more critical than others.

"The weight of the computers to not exceed 5 kg." is acceptable technical english.

However it is still needlessly wordy. It would be better to put all over-all requirements in a list and give a range of acceptable values:

weight: 4-5kg

or weight: <5kg

&quot;Shall&quot; and &quot;must are leftovers from the dark ages.

I will not use them, even under 961, when I can have a more easily read technically correct rewriten requirement.


(FYI. All of my work goes to NASA.)





procadman2
Proe Design & Admin
NASA Contractor

&quot;You can't build a reputation on something you haven't done.&quot;
H Ford

 

[ctopher]

procadman2
Well said. I agree and also follow your same guidelines.
I think 'shall' and some other sayings were brought into our language by the movie/tv industry ~30-40 years ago!