Architectural Models-I

Lecture 24 investigates macro architectural patterns and structural models. The curriculum examines the Repository (Blackboard) architectural model, where all shared data is managed in a central repository accessible to independent, loosely coupled subsystem components. Students analyze repository advantages—such as efficient data sharing without message-passing overhead and centralized backup and security—alongside disadvantages, including central bottlenecking and tightly coupled data schemas. The lecture then evaluates the Client-Server architectural model, analyzing how processing responsibilities are partitioned between service-requesting clients and service-providing servers across networked environments. Two-tier and multi-tier client-server variants are contrasted regarding network latency, scalability, and maintenance. State transition diagrams illustrate how event-driven systems transition between operational states in response to external triggers and guard conditions. The lecture contrasts traditional sequential lifecycle models like the Waterfall model against iterative, prototyping, and risk-driven evolutionary approaches. Software design principles emphasize high cohesion and low coupling to minimize ripple effects and enhance long-term system maintainability. Coupling classifications, spanning content, common, control, stamp, and data coupling, are critically evaluated to eliminate structural dependencies. Cohesion levels, from coincidental and logical to communicational and functional cohesion, provide objective criteria for evaluating module quality. Object-oriented analysis using the Coad and Yourdon methodology illustrates identifying classes, responsibilities, attributes, and services. Structural relationships, including Generalization-Specialization inheritance hierarchies and Whole-Part aggregation assemblies, are modeled with precision. Dynamic interaction modeling demonstrates sequence diagrams, object lifelines, activation bars, and synchronous versus asynchronous message exchanges. Software architecture frameworks explore Kruchten's 4+1 view model, connecting logical, process, development, and physical architectural perspectives. Architectural styles, including layered hierarchies, repository patterns, client-server structures, and pipe-and-filter pipelines, are contrasted. Design pattern principles demonstrate how Gang of Four solutions, such as the Observer pattern, decouple subjects from observers to handle state changes. Professional coding style standards detail clear identifier naming, consistent indentation, layout structure, and self-documenting code conventions. Defensive programming practices illustrate safe file handling, resource leak prevention, and robust input validation in C++ and Java environments. Exception handling mechanisms demonstrate try-catch-finally blocks, structured error propagation, and eliminating silent runtime failures.