Parameter Data Item (Configuration files)

Parameter Data Item is a new topic. It  is intended to address the possibility to produce and modify some configuration tables or databases separately from the executable object code. The guidance is applicable when such data is modified and the executable object code is not reverified.

The new text identifies two keywords “parameter data item” (general word) and “parameter data item file” (the executable representation of the PDI):

Parameter data item – A set of data that, when in the form of a Parameter Data Item File, influence the behavior of the software without modifying the Executable Object Code and that is managed as a separate configuration item. Examples include databases and configuration tables.

Parameter Data Item File – The representation of the parameter data item that is directly usable by the processing unit of the target computer. A Parameter Data Item File is an instantiation of the parameter data item containing defined values for each data element.

As the PDI file is separate from the executable object code, throughout the document multiple changes were performed to replace “executable object code” with “executable object code and Parameter Date Item Files”, as all considerations on generation, identification and management of the executable object code are applicable to the Parameter data Item Files.

The use of a PDI impacts all the processes:

  • A new section is added in the “Software Considerations in the System Life Cycle Processes” to highlight the possible impact on this approach on the system
  • During the planning process, processes applicable to PDI should be defined and described in the plans, in particularly in the PSAC, as additional considerations. The software load control and compatibility aspects should be also addressed
  • PDI is subject to High Level Requirements development. These requirements define the structure, attributes and (when applicable) the values. This is often called “usage domain”. The choice to consider these data as HLR and not LLR is to make the guidance applicable to level D software.
  • In the integration process, the PDI files are generated
  • Of key importance is the new section 6.6 on the verification of the PDI. This section defines under which conditions the verification of the PDI may be conducted separately from the executable object code. These conditions are tied to the coverage of the executable object code verification Demonstration that the executable object code is able to handle the PDI values inside the limits provided by the PDI HLR, and to be robust against invalid structures and/or attributes, needs to be provided.
  • The verification objectives on the PDI file itself, conducted separately, are defined, and summarized in the table A-5. The first objective is to verify that the PDI file is compliant with its HLR (structure, attributes), and that it doesn’t contain any unintended element. This objective includes also the verification of the correctness and consistency of the element values (not only that it is in the range defined in the HLR). The second objective is to verify the completeness of the verification.

It should be noted that the PDI file is identified as Software Life Cycle Data (§11.22), and is also the topic of a discussion paper (DP#20) in DO-248C/ED-94C, providing clarifications and examples.