Designing to The System Lifecycle

Requirements Analysis: Understand and analyze stakeholder requirements and identify key design drivers. Prove we understand what is being asked of us by the customer.

What does the system have to do? 

How does it fit into the larger system?

Activities:

Analyze/Refine stakeholder needs

Group stakeholder needs into functional and non-functional categories

Derive requirements from stakeholder needs

Link derived requirements to stakeholder needs

Define mission threads and use cases

Link requirements to system use cases

Prioritize mission threads and use cases

Functional Analysis: Develop the functional model of how the system behaves to meet the customer requirements and mission goals.  Understand the functional scenarios of system operation.

Functional Analysis is a top-down process of translating system level requirements into detailed functional and performance design criteria. Functions are analyzed by decomposing higher level functions identified through requirements analysis into lower-level functions.

The result of the process is a defined Functional Architecture with allocated system requirements that are traceable to each system function. 

During functional analysis, functions are analyzed by decomposing capabilities identified through requirements analysis to lower-level functions.

The functional requirements associated with the capabilities are allocated to functions.  

The result is a description of the product or item in terms of what it does logically and in terms of the performance required. 

What are some of the scenarios that the system has to work through (“blue sky” and “off nominal”)?  

What is the activity flow that has to happen within those scenarios? 

What are some of the functions that need to happen?

Activities: 

Define system functions needed to realize the system use cases

Define interactions between the functions to define the system functional flow

Create scenarios that map to use cases

Link system functions and interactions to requirements

Derive requirements

Perform gap analysis between functions/interactions and requirements

Perform the same activities for different levels of decomposition of the system.

Functional analysis is a system development tool used to capture required system functions.  The model contains functions, which are linked to use cases and requirements at the correct level of decomposition for traceability.  Functional analysis should remain implementation independent. Defines how the system must operate and the logical design of the system.

Design Synthesis: Develop a physical architecture that can perform the required functions within the constraints imposed by the performance requirements.

What does the physical architecture of the system need to be to implement the necessary functionality? 

What are the components of the system? 

What are the interactions of those components (what messages flow between?)? 

What does each component do, and when does the component function?

Primary Objective: Develop a physical architecture that can perform the required functions within the constraints imposed by the performance requirements.

Typical Activities: 

Perform Architectural Analysis and Trade Studies

Allocate functions established during functional analysis into the physical partitions from architectural analysis to establish the architectural baseline.

Decompose and derive requirements

Determine if reuse opportunities from legacy systems exist

Determine interfaces the system entities have with each other as well as with entities internal to the system.

Design synthesis can be done in series or in parallel with requirements and functional analysis.  Design synthesis defines the physical architecture.  Design synthesis is the process of translating the functional architecture developed during functional analysis and decomposing those functions into a physical architecture that satisfies required functions.  

Physical architecture is the physical layout of a system and its components in a schema.  A set of product, system, and/or software elements.  The correlation with functional analysis requires that each physical or software component meets at least one (or part of one) functional requirement, though any component can meet more than one requirement.  

The goal of design synthesis is to combine and restructure hardware and software components in such a way as to achieve a design solution capable of performing the required functions within the limits of the performance parameters prescribed.  During concept development, design synthesis produces system concepts and establishes basic relationships among the subsystems.  During preliminary and detailed design, subsystem and component descriptions are elaborated, and detailed interfaces between all system components are defined.  Since there are several candidate solutions (hardware and/or software architectures) developed to satisfy a given set of functional and performance requirements, Design Synthesis sets the stage for trade studies to select the best among the candidate architectures.  Assess the candidate solutions considering the defined scenarios, environments, Measures of Effectiveness (MOEs), Key Performance Parameters (KPPs) and other performance parameters.

Achieve a design solution capable of satisfying the stated requirements.