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Software Architecture Guide

Architecture Means

Explanation

Section titled “Explanation”

Architects do not start from a blank page. They draw on a toolbox of means. These means help them describe, shape and change a system.

Styles. An architecture style is a family of architectures that share characteristics. N-tier and microservices are examples. A style limits which elements and relationships are allowed. Those limits make desirable properties emerge. Styles do not require specific technologies, but some technologies fit certain styles better (see Architecture Style).

Tactics. A tactic is a design decision that influences how a system responds for one quality attribute, such as availability or performance. Quality attributes therefore guide the choice of tactics. Tactics are simpler and more primitive than patterns (see Architectural Tactic).

Patterns. A pattern usually balances several quality goals at once. A tactic does not. Tactics are put into practice through combinations of patterns, frameworks and code (see Architectural Pattern).

Basic architectures. N-tier is one example. It structures a whole application into logical layers and physical tiers. Each layer may only call the layers below it (see Layered Architecture).

Reference architectures. A reference architecture is a template generalized from a set of solutions. It is more concrete than patterns and styles.

Modelling means. Notations describe architectures. ISO/IEC/IEEE 42010 defines an architecture description language broadly as any form of expression used in architecture descriptions. So these languages count as modelling means.

Why it matters. The means you choose shape the fundamental decisions of the system. Those decisions are the basis for many detailed ones. They are recorded in the solution strategy (see Solution Strategy).

Example

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A team must build an online shop that stays responsive under load. They pick a style: N-tier, with a web layer, a business layer and a data layer. For fast responses, they apply a tactic. Then they implement it with a pattern and a framework. They draw the result in a standard notation. They write all these choices into the solution strategy.

Trade-offs

Section titled “Trade-offs”

More concrete means, such as a reference architecture, bring more reuse and structure. The price is that many decisions are made in advance. The architect loses freedom of choice.

Constraints from a style bring benefits but also challenges. It can be better to relax a constraint than to chase purity. Changing direction later is costly, so weigh the choice early.

Checks

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  • The solution strategy records the fundamental decisions, including which styles, patterns or tactics were chosen.
  • Each tactic named in the document is tied to the single quality attribute it addresses.
  • For each chosen style, the document states the constraints it imposes and the trade-offs accepted.
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Sources

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