Mikhail Sudbin

Mikhail Sudbin
Chief Technology Officer at Advalange

7 Tips That Can Make Your Software Tool Qualification Easier

Qualification (aka certification) of software tools is a common requirement in safety-critical engineering. Often this aspect of development life cycle raises many questions and issues. Below I summarized my experience in aerospace area into seven tips. Though the tips are tight to RTCA DO-178C and DO-330 standards, other safety-critical domains will benefit as well. Consider these tips to increase efficiency of your project.

Tip #1. Evaluate tool qualification criteria correctly

Normally you don’t need to qualify each single software tool. Identify tool usage scenarios precisely and evaluate them against qualification criteria stated in the standards. It’s like a court trial: the standard is a judge and you are a lawyer. You need to justify that your tool does not require higher level of qualification or qualification at all. If your arguments are reasonable and sound, you will be okay with the certification authority.

Tip #2. Consider tool chain usage accurately

Usually several tools are used consecutively to obtain a result. You need to make a wise choice. One option is to qualify every tool in the chain as a development tool. Another option is to add one more tool in the chain to check the result and qualify only this tool as a verification tool. Sometimes it’s more reasonable to add an additional verification tool even if the chain consists of a single development tool.

Tip #3. Qualify only required functionality

Once again, evaluate the tool usage scenario carefully. Often you need to qualify only a portion of functionality. In that case think about partitioning this functionality, otherwise you’ll have to qualify the tool completely. A good example is splitting a tool into a GUI application and a command line utility. The command line utility implements business logic and is being qualified. GUI is developed in a less rigorous way. Review of command line log serves as a bridge between these two components. Such an approach may save you considerable effort.

Tip #4. Remember about COTS tool qualification package issue

Overreliance on COTS tool qualification package may produce a number of sleepless nights. A tool provided with a qualification package from a vendor does not mean that you can proceed without further actions. In most cases, you need to do some additional activities such as running qualification tests and evaluating the results. Such additional tasks may take significant time. Moreover, a tool qualification package may require prerequisites that your target system cannot provide. For example, it may require a file system on your target to store intermediate data and results or an ability to debug step-by-step. Consider additional qualification efforts and package constraints when planning tool usage.

Tip #5. Balance your cost

Evaluate the total cost of tool qualification. Estimate the savings that this tool will bring to your project. Sometimes it’s more efficient from a time and budget perspective to refuse tool qualification and to conduct full cycle of verification activities for outputs of the tool. This is especially useful in the cases where a unique component is being created and there is no plan of further usage of the tool.

Tip #6. Timely plan tool qualification activities

Negotiate tool usage and qualification strategy with the authorities at the start of the project. Conduct tool qualification tasks along with system development. Evaluate COTS tool qualification package before deciding on tool usage. This advice may seem obvious. Many projects, however, start thinking about tool qualification several weeks prior deadline when there are many other functional and developmental troubles.  You will not have the luxury to spend valuable time wrapping up qualification things at that time.

Tip #7. Combine previous tips

Each of these seven tips is valuable on its own. However, you can achieve better results by combining them creatively. Try different tool chains and evaluate total implementation effort for different variants. Don’t be shy about adding COTS tools into chains of homemade tools. Transfer qualification tasks from development to verification tools by adding additional activities into your product life cycle. It’s like music: you have just seven notes but you can play thousands of melodies.

 

Recipe on software tool qualification

 

In conclusion, let me illustrate these seven tips with a practical example of parameter item data generation tool. The tool uses some portion of requirements presented in formal notation to generate a binary data file. The file is then uploaded into target.

Tip #1: This tool is definitely a development tool if we use its binary outputs without further review and testing. It should be qualified according to DO-330 TQL1-TQL3 depending on the system’s design assurance level.
Tip #5: Qualification of a development tool is an expensive task that may overwhelm the budget.
Tip #1, #2 and #5: The cost may be reduced by adding additional verification tool (DO-330 TQL5) and some manual verification into the chain.
Tip #3: We can minimize qualification effort by extracting data file generation functionality from GUI, setup and other components of the tool.

As a result parameter data item tool is transformed into:

  1. GUI, setup and other components that can be developed with any rapid architecture development technique. These components produce a kind of database (DB) file for further generation, for example in xml format. No qualification is needed.
  2. Command line utility that converts DB file into a binary file for target. In addition, this utility produces a .txt file which contains DB parameters and execution log information in human-readable form. Exact correspondence between DB file, binary file and human-readable .txt file is qualified according to the verification tool criteria.
  3. The process is complemented with an additional review step. A developer adds DB and text files into configuration management system along with the binary output. A verification engineer then checks that the information in the text file matches the requirements.

Thus, this example shows that an inventive approach can transform a costly qualification of a development tool into a far easier sequence of verification and utility qualification. However, don’t forget about tip #6 – any creative plan should be approved by the certification authority.