Task: Define Subsystem Physical Interfaces

This task refines the logical interfaces received from systems engineering into physical, realizable interfaces.

Disciplines: System Engineering Architecture

Purpose

The purpose of this step is to create physical, realizable interfaces from the logical interfaces received from systems engineering.

Relationships

Roles

Primary Performer:

Additional Performers:

Inputs

Mandatory:

Shared Model

Optional:

Outputs

Main Description

Systems engineering generally defines what is known as the "logical interface" between the system and its actors and among subsystems. The logical interfaces provides organizations of named services, (highly) abstract data types with ranges and constraints, and various quality of service parameters. In this task, the engineering staff must refine these logical interfaces in deployable physical interfaces. Requires the usage of services within defined APIs of existing equipment or agreements between teams on devices not yet developed. The services must be qualified with actual data schema (bit-mapped formats), and qualities of service.

Steps

Refine logical service into physical service

For all services within an interface, the means by which the service will be involked must be specified (TCP/IP? RS-232? UDP datagram?).

Refine data schema

For all parameters of all services (including return values), the bit-mapping of the formats must be determined explicitly. The logical information should specify the extent of the parameter (i.e. acceptable values) but the schema must define the storage and transmission format, bit ordering, and so on.

Refine constraints

Any quality of service constraints associated with an interface must be refined in the light of the invocation of the physical service(s) invoked and the data formats used.

Put physical interfaces into shared model

Physical interfaces between the system and the actors or between subsystems should be held within the shared model for easy, common access.

Baseline the interfaces

Put the interfaces under configuration control to ensure controlled changes and a common understanding of what is needed.

Review the physical interfaces

Review and evaluate the resulting physical interfaces between the system and its actors and between the subsystems in terms of consistency, adequacy, compliance with standards and known APIs and completeness. This includes service invocations, data structures, and quality of services aspects. The mapping between logical and physical may be complex - only in the simplest of systems is it 1:1.

Key Considerations

Every logical interface must be realized, but it may not be in a 1:1 way; it is common for a logical interface to result in many physical messages or machine motions that constitute the actual physical interface. In addition, logical interfaces should provide range and fidelity metadata on the parameters of the interface but not the physical data schema; the physical data scheme must be defined within this task.