6Integration, migration & maintenance

• 6.1Inter-system integration

  Covers REST APIs for loosely coupled HTTP-based integration, ETL for extracting, transforming, and loading data across systems, EAI for mediating heterogeneous in-house systems, and the criteria for choosing between synchronous integration (the caller waits for a response) and asynchronous integration (processing continues without waiting).

• 6.2Migration approaches and planning

  Covers the trade-offs among big-bang migration (cutting over all at once), phased migration (cutting over in stages by scope), and parallel migration (running old and new side by side for a period), data migration/conversion/verification, a pre-cutover rehearsal and rollback on failure, and the go/no-go decision on whether to proceed with the cutover.

• 6.3Testing and quality assurance

  Covers unit testing that verifies individual modules, integration testing that verifies interaction between modules, system testing that verifies the whole system meets business requirements, acceptance testing confirmed by the requester, performance testing that checks response under expected load and load testing that probes the limits, and the reliability growth curve that visualizes whether testing progress is on track.

• 6.4Development processes and DevOps

  Covers the sequential waterfall model, iterative development in small increments and its leading form, agile (Scrum), CI (continuous integration) that automates build and test and CD (continuous delivery/deployment) that automates through to release, and the four categories of maintenance by nature: corrective, adaptive, preventive, and perfective maintenance.