Interface

A connection point where a system meets its environment or where components connect to each other. The locus of exchange and interaction.

Formal Definitions

Mobus & Kalton (2015):

“The boundary B at level l is a tuple: B_{i,l} = ⟨P, I⟩ where P is the set of properties and I is the set of interfaces.”

(Principles of Systems Science, Section 4.3, Eq. 4.6)

Interfaces mediate environment-system flows through bipartite graphs:

“G is a bipartite flow graph where C’ and C” are subsets of components that receive inputs from source elements and send outputs to sink elements respectively.”

(Section 4.3, Eq. 4.5)

Bunge (1979): Bunge captures interface implicitly through action relations between components and environment:

“The A-environment of σ at time t is the set of all things… that act or are acted on by components of σ at t.”

The symbol ⊳ denotes “acts upon” — interfaces are where these actions occur.

(A World of Systems, Definition 1.2, Chapter 1)

Synthesis

Mobus explicitly defines interfaces as elements of the boundary that mediate flows through source-sink connections. Bunge captures the concept through action relations (⊳) without naming it separately. Both agree that interfaces are where meaningful exchanges happen — not passive boundaries but active sites of interaction.

Key Insight

Interfaces determine what can flow between system and environment. Well-designed interfaces enable necessary exchanges while maintaining system integrity. Poorly designed interfaces create bottlenecks or vulnerabilities.

Related Concepts

• Boundary — contains the interfaces
• Flow — what passes through interfaces
• Environment — what’s on the other side