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Model based system engineering gains broader acceptance

The general idea behind model based system engineering, or MBSE, is that it makes sense to design complex embedded software, or complex systems that are made up of hardware and software, before you start to build them.

"It is a dynamic and newish market," claimed Hedley Apperly, Atego's vp product and marketing. This company bases its solutions, including its newly released Atego Vantage, on the industry standard Unified Modelling Language (UML) and systems modelling language (SysML). "What people did before was build things up in this modular way in other industries, but not in the UML and SysML spaces," continued Apperly. "The way it was done in the past was to build very big, very big complex models. So what we have done is to apply best practices from other industries – using product families, modular design or component based construction – and applied them to UML and SysML."

One of the first MBSE platforms, launched in the early 1990s, was IBM's Rational suite, which has been developed since and is now the platform on which a broad range of products around the world have been designed. Greg Gorman, director of Rational Systems Product Management at IBM, commented: "MBSE allows you to investigate a wider range of designs, analyse them and select the most appropriate one for your problem space. The non-optimal designs are still available, especially if the end user needs change, so it is easier and faster to accommodate them."

And is MBSE consequently becoming more established? "I believe so," said Gorman. "One reason is simply because of cost. If I can create models and execute them for analysis, I can reduce the risk of bad design, selecting the wrong design, or just catch defects early. Organisations like the International Council on Systems Engineering have been holding MBSE workshops for several years to 'standing room only' crowds."

Moreover, as projects get ever more complex, there are less products where MBSE could not be used to good effect. "The combination of hardware, electronics, mechanical systems and complex software is getting more and more challenging, and engineers need tools like MBSE to help manage that complexity," said Gorman.

Gaining advantage
Atego has taken the MBSE philosophy further recently, with the launch of Vantage. This takes the recently updated Atego Modeller and adds two new approaches. One is product line engineering – taking a product family and then having individual variants on the core product. While it may be as simple as a function being switched on or off, it could involve complex combinations of functions, and so the modular approach of MBSE is ideal.

"The other idea," commented Apperly, "is that systems and software are built from modules or components – that is how people work in the real world. They have a PCB, a piece of software code or even a piece of mechanical hardware that they have in a library. When they build a new system, they can pull from those existing things. They might just be concepts as well as physical things. So we have provided an asset library for modular design that lets you build your concepts in those two modelling languages by dragging and dropping from a palette of existing things. And they all link together.

"You could, for example, design your software in UML and pull existing software components from your asset library. In this modular fashion, you could design a whole family, say 150% of the functionality and then you could make choices about which parts of this family will I build the product from and generate a whole model that is specific to that product, leaving out the bits of software you don't need. Then we can generate source code automatically from UML into things like C++ and Java."
The whole process, its proponents claim, becomes cheaper, easier and more reliable. Rather than writing code, the designer is abstracting; plugging together modules that exist and work, so problems can be found earlier in the process when they are cheaper to fix, and the quality of the design is improved.

In a report launched in March 2014, Embedded Market Forecasters claimed that, when compared to typical systems engineering, the addition of up front modelling and product line engineering delivered a 62% reduction in total development cost and that 23% more projects were delivered on time.

Using this approach is an advantage, even when there are no modules in the asset library. Apperly explained: "What it lets you do if you are starting afresh is to design, or architect, in a modular way. So you can, for example, build a system from, say, 20 sub-systems which don't yet exist. But I can then specify those 20 systems by using the definitions as contracts to pass on to other designers. It means you can then enable parallel working, off-site working or supplier/consumer relationships to build a system. It is a great way of making that top-down, modular design that gives you parallelism and outsourcing.

Of course, even ignoring reuse, that improves maintenance because you have pluggability – you can unplug one sub systems and plug in another because of the modular design. Typically, you get the reuse benefits when you get to project 2.3! But you do get benefits from modular design right from the first project."

Typically, users of MBSE are likely to be in sectors like aerospace, defence, automotive and rail. Asked why this is, Apperly responded: "It is interesting. From an aerospace and defence point of view, it is because they have massive systems. With embedded systems or software designed to run on a plane – those are projects run for a long time. They need to be maintained for as long as the plane is flying and they need very deep traceability and complexity.

"The same is true for automotive. There is a lot of safety criticality and obviously the same with rail. So having a trace from your requirements through to your design through to implementation of your hardware and your code is very important. Having said that, we have customers in the set top box market and in all other sorts of sectors. I think it is about complexity, safety, certification, traceability; those kinds of thing."

Another feature of Vantage is that it runs on a live database and is not file based. This, says Atego, makes it suited to use by the large, disparate and outsourced design teams typical in these projects, where sharing – or at least having access to – the core model at the same time can be important.

Tim Fryer

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