Specification tree explained

A specification tree shows all specifications of a technical system under development in a hierarchical order.

For a spacecraft system it has the following levels:

• System (requirements) specification - generated by customer
  • System (design to) specification - generated by system responsible prime contractor
    • Subsystem specifications - generated by system responsible prime contractor
      • Assembly^[1] specifications - generated by subsystem responsible contractors
        • Unit specifications - generated by subsystem (or assembly) responsible contractors.

Notes and References

1. An assembly level is defined as intermediate level when the subsystem contractor prefers to contract a group of units with complex interfaces to another contractor (for instance the operating system and subsystem application software can be an assembly of the data management subsystem).