Names are labels we give to things to provide mental holding places for what a thing is; I am Michael, author of this blog and you, dear folks, are my readers.(2) Humans are flexible and we can assign different names to the same thing and still know it is a rose. Computer programs however….
Many moons ago I wrote a post on naming conventions; (3) this is the first stage in the software “name game.” For software names have to be descriptive (with naming conventions) and unique.
Where things go wrong: Scope
Error, stop, fault, or startup: If you look into almost any set of code you will find these common variable names. If the variables are scoped to just the given module, things are okay, but often things “leak out.”
If you look at the interface variables, e.g. the bus (structures in C), enumerations, and all global data, you will see that enumerations, given the “state” nature, commonly reuse the same names.
ICD and Data Dictionaries
First, a note on the image. Since this is a blog on Names, the use of acronyms is especially important. When I write “ICD” I am thinking of Interface Control Documents; but it can also mean “Implantable Cardiovascular Device.” But enough side bars…
Our goal to have unique names (at the project scope) aided by two things; ICD and Data Dictionaries. The object here is to augment these base tools with integrity checking tools to validate full systems.
Tag the scope of data in the data dictionary: Enable scope detection for the data in the system.
Enforce naming rules: For both root and sub-data names.
It has always bothered me that the poem goes “Roses are red, violets are blue“; properly speaking violets are by their very name the color violet.
At some point in the future your role will change and you will have another name.
The image to the right is exactly what a naming convention looks like; everyone comes together and picks names.
Interface control documents (ICD) and data dictionaries are two parts of a mature MBD infrastructure. The question I often hear is “what is the boundary between the two artifacts”? First a high-level refresher:
The Data Dictionary: an artifact used to share a set of common data definitions external to the model and codebase.
Objective: provide common and consistent data definition between developers
The ICD: an artifact used to share interface information between components external to the model and codebase; often derived from or part of the requirements document set.
Objective: provide a common interface definition to simplify the integration of components when multiple people are working on a project.
An example of an ICD spec is
(double mintGum, single *thought, something *else)
And here is where the boundary question comes up. In specifying the data type and dimension in the ICD I am duplicating information that exists in the data dictionary; violating the single source of truth objective.
So what is the flow of information here? I would suggest something like this…
The ICD document is created as part of the initial requirement specifications
The data interface request is used to inform the initial creation of data in the data dictionary
Once created the data is owned by the data dictionary
Infrastructure: making your artifacts work for you
Data dictionaries serve an obvious purpose, they are a repository for your data. On the other hand, interface control documents can seem like a burdensome overhead; which it will be without proper supporting infrastructure. If you remember the objective of the ICD, to simplify integration, then the need for tool support becomes obvious. When a developer checks in a new component it should be
Checked against its own ICD
Checked against the ICD for functions it calls and is called by
Its ICD should be checked against the data dictionary to validate the interface definition
With those three checks in place, early detection of invalid interfaces will be detected and integration issues can easily be avoided.
ICDs and the MATLAB / Simulink environment
Recently MathWorks released the System Composer tool. While I have not had a chance to try it out yet it offers some of the functionality desired above. I would be interested to learn of anyone’s experience with the tool