Software Architecture Design

What is the scope of software architecture?

Opinions vary as to the scope of software architectures:

• Macroscopic system structure: this refers to architecture as a higher-level abstraction of a software system that consists of a collection of computational components together with connectors that describe the interaction between these components.
• The important stuff—whatever that is: this refers to the fact that software architects should concern themselves with those decisions that have a high impact on the system and its stakeholders.
• That is fundamental to understanding a system in its environment.
• Things that people perceive as hard to change: since designing the architecture takes place at the beginning of a software system's lifecycle, the architect should focus on decisions that "have to" be right the first time. Following this line of thought, architectural design issues may become non-architectural once their irreversibility can be overcome.
• A set of architectural design decisions: software architecture should not be considered merely a set of models or structures, but should include the decisions that lead to these particular structures, and the rationale behind them. This insight has led to substantial research into software architecture knowledge management.

What are the characteristics of software architecture?

Software architecture exhibits the following:

A multitude of stakeholders: software systems have to cater to a variety of stakeholders such as business managers, owners, users, and operators. These stakeholders all have their own concerns with respect to the system. Balancing these concerns and demonstrating that they are addressed is part of designing the system. This implies that architecture involves dealing with a broad variety of concerns and stakeholders, and has a multidisciplinary nature.

Separation of concerns: the established way for architects to reduce complexity is to separate the concerns that drive the design. Architecture documentation shows that all stakeholder concerns are addressed by modeling and describing the architecture from separate points of view associated with the various stakeholder concerns. These separate descriptions are called architectural views.

Quality-driven: classic software design approaches (e.g. Jackson Structured Programming) were driven by required functionality and the flow of data through the system, but the current insight is that the architecture of a software system is more closely related to its quality attributes such as fault-tolerance, backward compatibility, extensibility, reliability, maintainability, availability, security, usability, and other such –ilities. Stakeholder concerns often translate into requirements on these quality attributes, which are variously called non-functional requirements, extra-functional requirements, behavioral requirements, or quality attribute requirements.

Recurring styles: like building architecture, the software architecture discipline has developed standard ways to address recurring concerns. These "standard ways" are called by various names at various levels of abstraction. Common terms for recurring solutions are architectural style, tactic, reference architecture and architectural pattern.

Conceptual integrity: a term introduced by Fred Brooks in The Mythical Man-Month to denote the idea that the architecture of a software system represents an overall vision of what it should do and how it should do it. This vision should be separated from its implementation. The architect assumes the role of "keeper of the vision", making sure that additions to the system are in line with the architecture, hence preserving conceptual integrity.

Cognitive constraints: an observation first made in a 1967 paper by computer programmer Melvin Conway that organizations which design systems are constrained to produce designs which are copies of the communication structures of these organizations. As with conceptual integrity, it was Fred Brooks who introduced it to a wider audience when he cited the paper and the idea in his elegant classic The Mythical Man-Month, calling it "Conway's Law."

What is the motivation of software architecture?

Software architecture is an "intellectually graspable" abstraction of a complex system. This abstraction provides a number of benefits:

• It gives a basis for an analysis of software systems' behavior before the system has been built. The ability to verify that a future software system fulfills its stakeholders' needs without actually having to build it represents substantial cost-saving and risk-mitigation. A number of techniques have been developed to perform such analyses, such as ATAM.
• It provides a basis for the re-use of elements and decisions. A complete software architecture or parts of it, like individual architectural strategies and decisions, can be re-used across multiple systems whose stakeholders require similar quality attributes or functionality, saving design costs and mitigating the risk of design mistakes.
• It supports early design decisions that impact a system's development, deployment, and maintenance life. Getting the early, high-impact decisions right is important to prevent schedule and budget overruns.
• It facilitates communication with stakeholders, contributing to a system that better fulfills their needs. Communicating about complex systems from the point of view of stakeholders helps them understand the consequences of their stated requirements and the design decisions based on them. Architecture gives the ability to communicate about design decisions before the system is implemented when they are still relatively easy to adapt.
• It helps in risk management. Software architecture helps to reduce risks and the chance of failure.
• It enables cost reduction. Software architecture is a means to manage risk and costs in complex IT projects.