How Systems are Developed The Commercial Life Cycle Model Common form of the Software Life Cycle Used through the commercial, industrial, institutional government communities University of Houston Clear Lake Science and Computer Engineering James C. Helm, Ph.D.,P.E. Engineering Division Chair

Example Software Development Process This process illustrates the major steps and flow that might be typical of a DoD or major Government Contractor. The documents would be obtained from the DoD standard, MIL-STDs, or IEEE NASA Software Document Standard, Software Engineering Program, NASA- STD

Requirement Phase Deals with all kinds of requirements –system –software –hardware –human system Interface –human in the loop

Design Phase Normally consists of two parts –Preliminary Design –Detailed Design

Code Phase Implements the detailed design –Some form of programming language –Three possible coding options top-down bottom-up middle-out

Select Appropriate Compiler/ Assembler Select Appropriate Programming Support Environment Initiate Appropriate Controls Follow Standards & Conventions Establish Software Library Establish/ Retain Required Databases FROM DESIGN PHASE Develop Large Driver to Stimulate System Code Top Level CSC Then Next Level, etc. Final Integration is minimal Test Whole System Each Time TOP-DOWN Develop Several Drivers to Stimulate Subsystems Code CSCs as functional threads Integration is moderate throughout Test Each Functional Thread MIDDLE-OUT Develop many drivers to Stimulate CSUs Code CSUs separately Integration is Time Consuming Test Each CSU Extensively BOTTOM-UP Determine Optimum Coding Strategy & Sequence OPTION 2 OPTION 3 OPTION 1 Ready for I & t

Correlation Between Specifications and Test Match the kind of software being developed and the manner in which it is being implemented and integrated –Specification hierarchy –Test hierarchy

Integration and Testing Phase Major Activities shown on next slide Determine early the selection and specification of the optimum test strategy Select: tools, instrumentation, recording methods and SW drivers Select environment: hardware configuration and location of tests