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Months After Contract Award IGURE D-5. Common Subsystem builds a scenario to drive the data flow through the system, and orchestrating reconfigurations such as primary thread switchover to backup thread.

• Build 2. This was the first build of mission-critical components and achieved the initial capability to execute real mission scenarios. The three primary risks inherent in the mission scenarios were the timeliness of the display database distribution, the performance (resource consumption and accuracy) of the missile warning radar algorithms, and the performance of the user interface for several complex displays. Upon completion of build 2, several mission-oriented use cases could be executed, including the worst-case data processing thread and the worst-case control processing thread (primary-to-backup switchover).

• Build 3. This build contained the largest volume of code, including display format definitions, global type definitions, and representation specifications needed for validation of external interface transactions. Although the code was voluminous, much of it was produced automatically in a cookbook manner by constructing code generation tools. The remaining components allocated to build 3 included the external communications interface protocol handling, the completed user-system interface for the mission operators, the user-system interface for the computer support positions, the system services for mission reconfigurations, database resets, off-line data reduction, and the nuclear detonation algorithms. Although initially planned as one large build, this increment was later split into two more manageable releases, builds 3-1 and 3-2.

• Build 4. This build provided the final installment of missile warning algorithms for satellite early warning systems, the final installment of mission management and mission status displays, and the final installment of external communications interface processing.

• Build 5. In the middle of the Common Subsystem schedule, build 5 was added to coincide with a particular external interface (being built on a separate contract), the schedule for which had slipped so that it was not going to be available during its originally planned build (build 4). Consequently, the external interface was scheduled into an entirely new build.

The build sequence defined on CCPDS-R is a good example of the typical build sequence recommended in Section 10.4.

D.5.2 The Incremental Design Process

The individual milestones within a build included a preliminary design walkthrough (PDW), a critical design walkthrough (CDW), and a turnover review (TOR). The schedules for these milestones were flowed down from, and integrated with, the higher level project milestones (SRR, IPDR, PDR, and CDR). Figure D-6 provides an overview of a build's life cycle and the focus of activities.

Within a build, a well-defined sequence of design walkthroughs took place. These walkthroughs were informal, detailed, technical peer reviews of intermediate design products. They were attended by interested reviewers, including other designers, testers, and even stakeholders outside the software organization (customer, user, project systems engineering personnel). Attendance was usually kept to a small number of knowledgeable people, typically 10 to 20. The explicit focus of these reviews was the important components, the architectural interfaces, and the driving issues— namely, the 20% of the stuff that deserved scrutiny. Coverage across all requirements and components was not required.

The design walkthroughs were informal and highly interactive, and there was plenty of open critique. No dry runs were necessary. Technical issues were noted as action items and tracked to closure. PDWs and CDWs usually lasted one or two days, with each of the participating CSCI managers responsible for presenting appropriate material.

Integrated Structural Demonstration

PDW Structure »

Integrated Performance Demonstration

Baseline Turnover Assessment

CDW TOR Completeness

Behavior A and accuracy a Maintenance

Prototypes and

Informal

Enhancements

Formal

Test and

refinements

baseline

baseline

maintenance

Component design and integration

Component evolution and maintenance

Component design and integration

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