What if ... Source code part of the SDS (Software Design Specification)

yodon

Staff member
Super Moderator
#11
Agree with c.itch to a point. I DO generally see SRSs written prior to software development. In fact, the developers are typically begging for it! But that's sliding off topic a bit. Anyway, agree that the V model is not required. Neither is 13485 but pushing through regulatory without 13485 compliance is more challenging. Similarly, if you try to take a radical (i.e., not state of the art / common practice) approach to software development it will likely get higher scrutiny. I find SDDs to be marginally useful. If they are needed to lay out an algorithm or to document design decisions that aren't obvious, then they're useful. We take a minimalist approach and generally have, for design, an architecture diagram, maybe some state models, and anything that is not obvious. But as c.mitch points out, I would not submit source code as design. That, to me, is just waving a red flag in their face.
 
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robert.beck

Involved In Discussions
#12
From a practical point of view, in my limited experience with about 8 510k projects that had significant software components and about an equal number with firmware as an important component, the software developers and project managers don't understand what an SDS is let alone what its value is. FDA should either drop it from the list of required documents, or do a much better job explaining what it's supposed to document. The other documents in the guidance make intuitive sense, or don't take much explaining to get their rationale across.

the SDS always stands out as an outlier - what it is, why do we need to do it, and can we just combine it with the SRS or the architecture?

I usually do the SDS after the fact, but keep it consistent with the architecture.

In response, to other comments on this thread, I don't see how source code can be part of SDS. source code is the medical device. it's the final output, not some intermediate step along the way. granted that source code should be expected to change in response to requirement changes and detected bugs, but this malleability doesn't make it either an SDS or an SRS.

I have observed this scenario often enough that it seems normal:

1) there is a discussion about what the software is supposed to do.
2) some coding happens.
3) somebody generates a flow chart or an architecture diagram that describes what this early version of the software does.
4) there is more discussion, and new requirements and constraints are spoken of.
5) the flow chart is updated.
6) then the final coding is done.
7) it's checked against the flow chart, and either or both are modified as necessary.
8) there are multiple rounds of testing until the software is done.
9) at this point, it's possible to write the SRS, architecture, hazard analysis. The overall device hazard analysis (assuming this is not a software-only device) has been long done, and it may be supplemented now that the software is completed. the product specifications were also done a long time ago, and they may be supplemented now that the exact role of the software is known. Steps 7 and 8 may take a long time and include many iterations.
 
#13
Hi Everyone,

This topic is very old, but I wanted to add a small comment to a statement mentioned by sagai that was probably overlooked. :2cents:

sagai said:
"... other topic but what if the unit test code is considered as a specification for the source code?"

Maybe you were talking about something different, but I think you are refering to "Test Driven Requirement"

(There are interesting articles in the web about this subject)

Do you see this happening anytime soon in the Medical Device Software Development world?
 
R

robertjbeck

#14
i have seen test driven development (TDD) recently for two simpler medical devices.

in one case, the developer called what he was doing TDD but it was not; he did not really understand what this meant. however, he did some other interesting things that worked very well for verification, and I don't know if they have a formal name.

in another case, the software group started writing test cases before requirements specifications. this got the quality/regulatory department upset because they thought it was an attempt to write software without having requirements, but it was actually a good process.
 
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