Engineering is just about wielding tools to solve problems. You don't need to use formal methods to do engineering in general. Sometimes they're useful; sometimes they're required; often they just get in the way.
In the context of software vs other sub-disciplines, the big difference is in the cost of iterating and validating. A bridge has very high iteration cost (generally, it must be right first time) and validation is proven over decades. Software has very low iteration cost, so it makes much more sense to do that over lots of upfront design. Validation of software can also generally be implemented through software tools, since it's comparatively easy to simulate the running environment of the software.
Other disciplines like electronics live a little closer to a bridge, but it's still relatively cheap to iterate, so you tend to plan interim design iterations to prove out various aspects.
"In the context of software vs other sub-disciplines, the big difference is in the cost of iterating and validating."
People forget that software is used in those other disciplines. CFD, FEA, model-based design etc. help to verify ideas and design without building any physical prototype and burning money in the real lab.
You can do some strain and stress analysis on a virtual bridge to get a high degree of confidence that the real bridge will perform fine. Of course, then you need to validate it at all stages of development, and at the end perform final validation under weight.
The thing is that people building engines, cars, planes, sensors, PCBs and bridges actually do so, largely because they are required to do so. If you give them freedom to not do that, many of them will spare themselves such effort. And they understand the principles of things they are working on. No one requires any of that from someone that glued together few NPM packages with a huge JS front-end framework, and such person may not even know anything about how the HTTP works, how browser handles the DOM etc. It's like having a mechanical engineer that doesn't even understand basic principles of dynamics.
There are industries that deal with the software (i.e. controls design) that have much higher degree of quality assurance and more validation tools, including meaningful quantitative criteria, so it clearly is not a matter of software vs hardware.
> Engineering is just about wielding tools to solve problems.
By that standard, doctors and hair stylists are also engineers, as are some chimps and magpies. I don't think it's a useful definition, it's far too broad.
> In the context of software vs other sub-disciplines, the big difference is in the cost of iterating and validating.
No, the big difference is that in the Engineering disciplines, engineers are responsible end-to-end for the consequences of their work. Incompetence or unethical engineers can and regularly do lose their ability to continue engineering.
It's very rare that software developers have any of the rigour or responsibilities of engineers, and it shows in the willingness of developers to write and deploy software which has real-world costs. If developers really were engineers, they would be responsible for those downstream costs.
There are plenty of engineering of physical things where nobody has or takes responsibility. Equally, there's plenty of examples of software where careful processes are in place to demonstrate exactly the responsibilities you discuss.
>Engineering is just about wielding tools to solve problems. You don't need to use formal methods to do engineering in general.
Way to general to be useful. By that definition the store clerk is an engineer (tool cash register, problem solved my lack of gummy bears), janitors swinging a mops, or automotive techs changing oil.
It wasn't a definition. Everything an engineer does is wield tools to solve problems. That doesn't mean wielding tools to solve problems automatically makes you an engineer. That said, I'm much less restrictive in those I would class as "doing engineering" than many.
In the context of software vs other sub-disciplines, the big difference is in the cost of iterating and validating. A bridge has very high iteration cost (generally, it must be right first time) and validation is proven over decades. Software has very low iteration cost, so it makes much more sense to do that over lots of upfront design. Validation of software can also generally be implemented through software tools, since it's comparatively easy to simulate the running environment of the software.
Other disciplines like electronics live a little closer to a bridge, but it's still relatively cheap to iterate, so you tend to plan interim design iterations to prove out various aspects.