July 1, 1997

3 Min Read
Reducing Development Timewith Requirements Management

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI July 1997 Column


A requirements management system enables engineers to track the functions, behaviors, and performance of a design's specifications.

A requirements management system (RMS) is the primary tool for defining what a device must do. Properly executed, such a system, which usually consists of a computer and a database, can reduce development time and cost. Because it provides validated specifications, an RMS reduces design iterations.

Figure 1. A general block diagram of a typical system.

An RMS captures requirements from all sources for all aspects of the product. It also allows multiple levels of abstraction, from a black box (understanding only what goes in and what comes out), to a gray box (understanding the product's functions and behaviors), to a white box (understanding exactly how the product is made). Such a tool allows designers to partition and allocate requirements to the desired level of abstraction, and provides traceability of each requirement. An RMS also controls key interfaces that evolve from partitioning the requirements. The system uses analysis and simulation tools to provide requirements validation, and can generate black-, gray-, or white-level specifications. An RMS can provide a matrix indicating compliance with verification and validation activities and generate management data on the requirements process.


An RMS can define product requirements in terms of function (what is required), behavior (how it is achieved), or performance (how well it is achieved--usually a numerical value). The system should define requirements in engineering terms that result in process (function), logic (behavior), and capability (performance) equations. For this process, high-level user or marketing requirements must be translated into quantifiable engineering design requirements that can be incorporated into the design.

Analysis and Simulation. An RMS should evaluate and validate requirements through the use of mathematical models of them. It should contain a simulation engine to simulate function and behavior equations. A performance-modeling engine enables the system to evaluate tolerance bands against requirements. Sensitivity studies and Monte Carlo simulations, which estimate variations by selecting random distributions, help engineers partition and allocate requirements to compensate for manufacturing variations and variations in the environment over the life of the equipment. An ideal RMS has built into it--or has an interface to--a safety analysis engine for hazard analysis, failure mode and effects analysis (FMEA), and fault tree analysis.

Verification and Validation. The system should draw information from the database of requirements to generate a compliance matrix that indicates that all requirements are verified at least once in the development process. Along with the prototype construction schedule, this matrix enables engineers to efficiently plan and execute verification of engineering requirements.

Management Functions. An RMS should provide a view of the management and regulatory requirements to enable engineers to assess the status of the requirements generation and verification process, ensure a successful transfer of the requirements to manufacturing (design transfer), and provide a log of the requirements process for the device's design history file.

Interfaces. Ideally the system should interface with other systems in the development process. The RMS should be linked directly to design output. This internal design or engineering group is the primary recipient of RMS-generated data. The system should also be linked to a project management system to enable a project manager to allocate resources, and to a document control system to track controlled copies of the specifications. Linking these systems enables design reviews to be a routine part of the review process. This provides engineers and designers with a tool to incorporate, control, and track crucial requirements into the design of a product.

Edward V. LaBudde is managing director of LaBudde Systems (Westlake Village, CA).

Copyright ©1997 Medical Device & Diagnostic Industry

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