# Layer 0: Holons
## Holonic Structure (Layer 0)
Layer 0 provides a common way of describing everything in the MAP. It is based on the concept of a [***holon***](https://en.wikipedia.org/wiki/Holon_\(philosophy\)). The term *holon* was coined by Arthur Koestler in his 1968 book, [**The Ghost in the Machine**](https://en.wikipedia.org/wiki/The_Ghost_in_the_Machine). Every *holon* is *both* part of a larger whole *and* a container for other holons. In other words, every holon is, simultaneously, both a part and a whole.
There are several aspects of holons worth noting as we will seem them playing out in the MAP again and again.
* ***Holons have inward and outward aspects***. This follows directly from their simultaneously being wholes and parts. For Koestler, these two aspects or "faces" evoke the two-faces of the Roman God Janus (hence his reference to Janus in the above excerpt). From the perspective of a holon's *wholeness*, one may look *inward* to its constituent elements. From the perspective of a holon's *partness*, one may look *outward* to its siblings and containing holon(s). This dichotomy is echoed in the MAP's distinction between [Agent I-Spaces and We-Spaces](https://evomimic.gitbook.io/map-book/map-foundations/broken-reference) and also directly informs the visual design of the MAP's presentation sub-system: [DAHN](https://evomimic.gitbook.io/map-book/map-foundations/broken-reference).
* ***Each holon has integrity and identity while simultaneously being a part of a larger whole (itself a holon)***. Each MAP holon has a unique identifier.
* ***Stable holons exhibit a homeostatic balance between the self-assertive and integrative tendencies***. The *integrative tendency* is expressed in the *MAP L0 Ontology* by a *holonic\_\_attraction* property on the relationship between two holons to indicate how strongly holon instances are attracted to one another via that relationship. This acts somewhat analogously for holons as the strong nuclear force does for atomic nuclei in physics. A sufficiently strong *holonic*\_attraction pulls the related holon *inside* the membrane of the relating holon. In semantic modeling terms, *holonic\_\_attraction* can be used to model relationship semantics as a continuum between *weak association* (low attraction), *aggregation* (moderate attraction) and *composition* (strong attraction).
* ***Holons are active subjects, not passive objects***. More than just information containers, MAP holons can perform actions.
Everything in the MAP is an instance of a *holon type, action type, property type* or a *holon relationship*. Holons have *properties*, can be *related to other holons* and can perform *actions.* The inclusion of actions in the MAP definition of holons reframes holons from being *passive containers of information* to *active participants -- i.e.,* from *objects* to *subjects.* The implications of this shift are profoundly expressed by Thomas Berry in [Evening Thoughts: Reflecting on Earth as Sacred Community](https://thomasberry.org/quote/evening-thoughts-reflecting-on-earth-as-sacred-community/):
> The universe is composed of subjects to be communed with, not objects to be exploited. Everything has its own voice. Thunder and lightning and stars and planets, flowers, birds, animals, trees, \~\~ all these have voices, and they constitute a community of existence that is profoundly related.
Thomas Berry, [Evening Thoughts: Reflecting on Earth as Sacred Community](https://thomasberry.org/quote/evening-thoughts-reflecting-on-earth-as-sacred-community/)
In the MAP, every holon has its own voice.
Property values do not have existence independent of their holon and do not have unique identifiers. For example, a Person holon may have `first_name` and `last_name` properties.
Furthermore, each holon comes with its own description. Layer 0 specifies what information is included in these descriptions.
Because everything in the MAP is ***self-describing***, whenever a subject is encountered, you can ask it:
* What *type* of holon are you?
* What types of *properties* do you have?
* What other *holons* are you related to?
* What *actions* can I ask you to perform?
The presence of descriptors for everything in the MAP allows MAP software to work with subjects whose types it has not encountered before. At this abstract level, *holons* and *relationships* form a *node/link* *structure* (graph) that supports navigation, search, visualization, modification and composition.
The *MAP Security Model* is also expressed in terms of this holonic structure. So the above questions can be more accurately reframed as:
* What *type* of holon are you?
* What types of *properties* do you have, *that you are willing to share with me*?
* What other *holons* are you related to, *that you are willing to share with me*?
* What *actions* *are you willing* to have me ask you to perform?
Tying the *MAP Security Model* to Layer 0 allows general-purpose security mechanisms to be implemented and evolved in the *MA*P Core, off-loading this burden from implementers of the *MAP Extensibility Layers*.
discuss MAP Meta-Space here?
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