Software architecture building blocks are the fundamental elements used to construct a system's design. They exist at various levels of abstraction.

Component (B): A primary, high-level, and often deployable unit of functionality. It is a cornerstone of modern architectural description.

Class (D): In object-oriented systems, a class is a fundamental structural element. Key classes that define the core domain or system services are architecturally significant.

Package (H): A mechanism for organizing other elements like classes and components. It defines namespaces and controls dependencies, making it a crucial structural building block.

Algorithm (A): A specific, key algorithm can be an architectural building block. The choice of an algorithm (e.g., for encryption or data processing) is a critical design decision that directly impacts quality attributes like performance and security.

C. a test harness: This is part of the testing infrastructure used to verify the system; it is not a constituent part of the product's architecture itself.

E. a processor: This is a hardware component. While a system's deployment view maps software to hardware, the processor itself is not a software building block.

F. a method/procedure/function/operation: These are generally considered too fine-grained. They are implementation details contained within larger architectural elements like classes or components.

G. a local variable: This is a very low-level implementation detail confined within a single method and holds no architectural significance.

1. ISAQB e.V. (2019). Certified Professional for Software Architecture

Foundation Level

Syllabus

Version 3.0.1. Section 2.2

"Building Blocks

" p. 11. This section explicitly lists "components

" "classes

" and "packages" as examples of building blocks. It emphasizes that architects decide on the building blocks and their granularity.

2. Bass

L.

Clements

P.

& Kazman

R. (2021). Software Architecture in Practice (4th ed.). Addison-Wesley Professional. Chapter 2

"What Is Software Architecture?". This foundational text defines architecture in terms of its constituent elements (components

connectors

and data)

which are the primary building blocks. Classes and packages are common ways to realize these components.

3. Clements

P.

Bachmann

F.

Bass

L.

Garlan

D.

Ivers

J.

Little

R.

Merson

P.

Nord

R.

& Stafford

J. (2010). Documenting Software Architectures: Views and Beyond (2nd ed.). Addison-Wesley. In Chapter 9

"Component-and-Connector Viewtype

" the documentation for a component often includes "information such as... significant algorithms it uses

" confirming that key algorithms are architecturally relevant details tied to building blocks.