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The architecture of a system describes its major components, their relationships (structures), and how they interact with each other. Software architecture and design includes several contributory factors such as Business strategy, quality attributes, human dynamics, design, and IT environment.
We can segregate Software Architecture and Design into two distinct phases: Software Architecture and Software Design. In Architecture, nonfunctional decisions are cast and separated by the functional requirements. In Design, functional requirements are accomplished.
Architecture serves as a blueprint for a system. It provides an abstraction to manage the system complexity and establish a communication and coordination mechanism among components.
Software design provides a design plan that describes the elements of a system, how they fit, and work together to fulfill the requirement of the system. The objectives of having a design plan are as follows −
It comes before the detailed design, coding, integration, and testing and after the domain analysis, requirements analysis, and risk analysis.
The primary goal of the architecture is to identify requirements that affect the structure of the application. A well-laid architecture reduces the business risks associated with building a technical solution and builds a bridge between business and technical requirements.
Some of the other goals are as follows −
Software architecture is still an emerging discipline within software engineering. It has the following limitations −
A Software Architect provides a solution that the technical team can create and design for the entire application. A software architect should have expertise in the following areas −
Quality is a measure of excellence or the state of being free from deficiencies or defects. Quality attributes are the system properties that are separate from the functionality of the system.
Implementing quality attributes makes it easier to differentiate a good system from a bad one. Attributes are overall factors that affect runtime behavior, system design, and user experience.
They can be classified as −
Reflect the structure of a system and organization, directly related to architecture, design, and source code. They are invisible to end-user, but affect the development and maintenance cost, e.g.: modularity, testability, maintainability, etc.
Reflect the behavior of the system during its execution. They are directly related to system’s architecture, design, source code, configuration, deployment parameters, environment, and platform.
They are visible to the end-user and exist at runtime, e.g. throughput, robustness, scalability, etc.
Quality scenarios specify how to prevent a fault from becoming a failure. They can be divided into six parts based on their attribute specifications −
The following table lists the common quality attributes a software architecture must have −
|Design Qualities||Conceptual Integrity||Defines the consistency and coherence of the overall design. This includes the way components or modules are designed.|
|Maintainability||Ability of the system to undergo changes with a degree of ease.|
|Reusability||Defines the capability for components and subsystems to be suitable for use in other applications.|
|Run-time Qualities||Interoperability||Ability of a system or different systems to operate successfully by communicating and exchanging information with other external systems written and run by external parties.|
|Manageability||Defines how easy it is for system administrators to manage the application.|
|Reliability||Ability of a system to remain operational over time.|
|Scalability||Ability of a system to either handle the load increase without impacting the performance of the system or the ability to be readily enlarged.|
|Security||Capability of a system to prevent malicious or accidental actions outside of the designed usages.|
|Performance||Indication of the responsiveness of a system to execute any action within a given time interval.|
|Availability||Defines the proportion of time that the system is functional and working. It can be measured as a percentage of the total system downtime over a predefined period.|
|System Qualities||Supportability||Ability of the system to provide information helpful for identifying and resolving issues when it fails to work correctly.|
|Testability||Measure of how easy it is to create test criteria for the system and its components.|
|User Qualities||Usability||Defines how well the application meets the requirements of the user and consumer by being intuitive.|
|Architecture Quality||Correctness||Accountability for satisfying all the requirements of the system.|
|Non-runtime Quality||Portability||Ability of the system to run under different computing environment.|
|Integrality||Ability to make separately developed components of the system work correctly together.|
|Modifiability||Ease with which each software system can accommodate changes to its software.|
|Business quality attributes||Cost and schedule||Cost of the system with respect to time to market, expected project lifetime & utilization of legacy.|
|Marketability||Use of system with respect to market competition.|