Notes

Software Architecture and Design - Goals, Principles plus some Key Considerations
Philippe Kruchten, Grady Booch, Kurt Bittner, and Rich Reitman derived and refined a definition of architecture based on work by Mary Shaw and David Garlan (Shaw and Garlan 1996). Their definition is:

"Software architecture encompasses the set of significant decisions about the organization of a software system like the collection of the structural elements and their interfaces by which the system is made up; behavior as specified in collaboration the type of elements; composition of these structural and behavioral elements into larger subsystems; and an architectural style that guides this organization. Software architecture also involves functionality, usability, resilience, performance, reuse, comprehensibility, economic and technology constraints, tradeoffs and aesthetic concerns."

In Patterns of Enterprise Application Architecture, Martin Fowler outlines some typically common recurring themes when explaining architecture. He identifies these themes as:

"The highest-level breakdown of something into its parts; the decisions which are Hard to change; there are multiple architectures in a system; what is architecturally Significant can transform over a system's lifetime; and, in the end, architecture boils Down to whatever the important stuff is."

Software application architecture may be the process of defining and coming up with a solution that's well structured and meets all the technical and operational requirements. The architecture will be able to take into account and improve upon the normal quality attributes such as for example performance, security, and manageability.

The main focus of the Software architecture is how the major elements and components within an application are employed by, or interact with, other major elements and components within the application. Selecting data structures and algorithms or the implementation details of individual components are design concerns, they are not an architectural concerns but sometimes Design and Architecture concerns overlap.

Before starting the architecting of any software, there are a few basic questions that people should strive to get answers for. They are as follows:

How the users of the system will be interacting with the system?

How will the application be deployed into production and managed?

What are the various non-functional requirements for the application form, such as for example security, performance, concurrency, internationalization, and configuration?

How can the application be designed to be flexible and maintainable over time?

What are the architectural trends that may impact the application now or after it has been deployed?

Goals of Software Architecture

Building the bridge between business requirements and technical requirements may be the main goal of any software architecture. The purpose of architecture is to identify the requirements that affect the essential structure of the application form. Good architecture reduces the business enterprise risks associated with creating a technical solution while a good design is flexible enough to handle the changes that will occur as time passes in hardware and software technology, in addition to in user scenarios and requirements. An architect must think about the overall aftereffect of design decisions, the inherent tradeoffs between quality attributes (such as performance and security), and the tradeoffs required to address user, system, and business requirements.

Principles of Software Architecture

The essential assumption of any architecture should be the belief that the design will evolve as time passes and that one cannot know everything one have to know up front. The design will generally have to evolve during the implementation stages of the application form as one learn more , so when one tests the design against real world requirements.

Keeping the above statement at heart, let's make an effort to list down a number of the Architectural principles:

The system should be created to change rather than building to last.

Model the architecture to analyze and reduce risk.

Use models and visualizations as a communication and collaboration tool.

The key engineering decisions ought to be identified and applied upfront.

Architects should consider utilizing an incremental and iterative method of refining their architecture. Start with baseline architecture to get the big picture right, and then evolve candidate architectures as you iteratively ensure that you improve one's architecture. Do not try to get it all right the first time-design just as much as you can so as to start testing the design against requirements and assumptions. Iteratively add details to the design over multiple passes to make certain that you get the big decisions right first, and then focus on the details. A common pitfall is to dive in to the details too quickly and get the big decisions wrong by making incorrect assumptions, or by failing to evaluate your architecture effectively.

When testing your architecture, think about the following questions:

What were the primary assumptions that were made while architecting the system?

What are the requirements both explicit and implicit this architecture is satisfying?

What are the key risks with this architectural approach?

What countermeasures are in place to mitigate key risks?

In what ways is this architecture an improvement over the baseline or the final candidate architecture?

Design Principles

When getting started with Software design, one should bear in mind the proven principles and the principles that adheres to minimizes costs and maintenance requirements, and promotes usability and extensibility. The main element principles of any Software Design are:

Separation of concerns: The key factor to be considered is minimization of interaction points between independent feature sets to accomplish high cohesion and low coupling.

Single Responsibility principle: Each component or module should be independent in itself and in charge of only a specific feature or functionality.

Principle of Least Knowledge: A component or object should not find out about internal details of other components or objects.

Don't repeat yourself (DRY): The intent or implementation of any feature or functionality ought to be done at only one place. It will never be repeated in a few other component or module

Minimize upfront design: This principle can be sometimes referred to as YAGNI ("You ain't gonna require it"). Design only what's necessary. Specifically for agile development, you can avoid big design upfront (BDUF). If the application form requirements are unclear, or if you have a possibility of the look evolving over time, you need to avoid making a large design effort prematurely.

Design Practices

Keep design patterns consistent within each layer.

Do not duplicate functionality within an application.

Prefer composition to inheritance. When possible, use composition over inheritance when reusing functionality because inheritance escalates the dependency between parent and child classes, thereby limiting the reuse of child classes. This reduces the inheritance hierarchies, that may become very difficult to deal with.

Establish a coding style and naming convention for development.

Maintain system quality using automated QA techniques during development. Use unit testing and other automated Quality Analysis techniques, such as for example dependency analysis and static code analysis, during development

Not only development, also think about the operation of your application. Determine what metrics and operational data are required by the IT infrastructure to ensure the efficient deployment and operation of one's application.

Application Layers: While architecting and designing the system, one needs to carefully consider the various layers into which the application will be divided. There are several key considerations that need to be considered while doing that:

Separate the regions of concern. Break your application into distinct features that overlap in functionality less than possible. The advantage of this approach is a feature or functionality can be optimized independently of other features or functionality

Be explicit about how layers communicate with one another.

Abstraction ought to be used to implement loose coupling between layers.

Do not mix various kinds of components in the same logical layer. For instance, the UI layer shouldn't contain business processing components, but rather should contain components used to take care of user input and process user requests.

Keep the data format consistent inside a layer or component.
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