Where does encapsulation collide?

In object-oriented programming, encapsulation is the discipline of bundling a piece of data together with the operations that act on it, and hiding the internal representation behind a fixed public interface, so that other code depends only on what the object does and not on how it stores its state. The idea grows directly out of Parnas's 1972 On the criteria to be used in decomposing systems into modules, which argued that each module should hide a design decision likely to change and expose only a stable interface. The referent is a rule of software structure: a boundary drawn in code around data and behavior. It has nothing to do with an immune cell walling off a parasite, a mental module cut off from outside knowledge, or a drug sealed inside a protective shell.[1]

Unit

One class or module: a data structure plus the methods allowed to touch it, behind a public interface

Recovery means

Not applicable

Measured by

Assessed by how much internal state is kept private, and whether callers depend only on the public interface

In insect immunity, encapsulation is a cellular defense in which blood cells, called hemocytes, surround an invader too large to be engulfed by a single cell, such as a parasitic wasp egg or a nematode, and build a dense, multilayered capsule around it that isolates and often kills it. Lavine and Strand's 2002 Insect hemocytes and their role in immunity reviewed how hemocytes recognise foreign surfaces and cooperate to form this capsule, which is frequently darkened by melanin. The referent is a living tissue response inside a body, judged by whether a foreign object ends up sheathed in cells. It is a wholly different thing from a boundary drawn around data in a program, a cognitive module cut off from belief, or a manufactured drug particle.[2]

Unit

One capsule: layers of hemocytes sheathing a single foreign body

Recovery means

The capsule may be cleared slowly as the walled-off invader dies and is broken down

Measured by

Scored by microscopy of implanted or injected targets, counting encapsulated objects and capsule thickness

In cognitive science, informational encapsulation is the property Fodor proposed as a hallmark of a mental module: a processing system is encapsulated when it cannot consult information held elsewhere in the mind while it works, so it runs on its own limited database and ignores what the rest of the mind believes. Fodor's 1983 The Modularity of Mind offered the persistence of visual illusions as evidence, noting that one line still looks longer than another even after you have learned the two are equal. The referent is an abstract limit on how a mental process can reach knowledge, not a physical wall. It differs sharply from data hidden inside a software object, cells surrounding a parasite, or a coating wrapped around a drug.[3]

Unit

One module's fixed database, walled off from the rest of the mind

Recovery means

Not applicable

Measured by

Inferred from behavior, such as illusions and reflexes that persist despite contrary knowledge