Why MBSE Still Needs Documents

A lot of people are pushing Model-Based Systems Engineering (MBSE) in a way to just deliver models … and by models they mean drawings. The drawings can and should meet the criteria provided by the standards, be it SysML, BPMN, or IDEF. But ultimately as systems engineers we are on the hook to deliver documents. These documents (specifications) form the basis for contracts and thus have significant legal ramifications. If the specifier uses a language that everyone does not understand and only supplies drawing in the model they deliver, confusion will reign supreme. Even worse, if the tool does not enforce the standards and allows users to put anything on the diagram, then all bets are off. You can imagine that the lawyers salivate over this kind of situation.

But it’s even worse really, because not only are diagram standards routinely ignored, but so are other best practices, such as including a unique number on every entity in the database or a description of each entity. As simple as this sounds, most people ignore doing these simple things until later, if ever. This leads us to our first question:  1) Is a model a better method to specify a system?

This question requires us to look at the underlying assumption behind delivering models vs. a document. The underlying assumption is that the model provides a better communication of the complete thoughts behind the design so that the specification is easier to understand and execute. Which leads us to the next question: 2) Can a document provide the same thing?

Not if we use standard office software to produce the document. The way it is commonly done today is that someone writes up a document in a tool like MS Word and then that files is shipped around for everyone to comment on (using track changes naturally) and then all the comments are adjudicated in a “Comment Matrix.” Once that document is completed someone converts it to PDF (a simple “Save as …” in MS Word). In the worst case, someone prints the document and scans it into a PDF. Now we have lost all traceability or even the ability to hyperlink portions of the information to other parts of the design, making requirements traceability very difficult.

However, if you author your document in a tool like Innoslate, you can use its Documents View to create the document as entities in the database. You can link the individual entities using the built-in or user created relationships to trace to other database entities, such as the models in the Action Diagram, or Test Cases. This provides traceability to both a document and the models. In fact, the diagrams in Innoslate can be embedded in the document as well, thus keeping it live, reducing the configuration management problem inherent in the standard approach.

MBSE doesn’t mean the end of documents but using models to analyze data and create more informative documents. Using a tool like Innoslate lets you have the best of both worlds: documents and models in one complete, integrated package.