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====== F1x Architecture ======

===== Overview =====

==== Terminology ====

* Site - F1x node installation
  * Identity - public/private keypair
  * RealmID - hash of Identity public key
  * Realm - set of objects that are related to an Identity. All shards in realm have the same realm ID. \\ Likely to be implemented as git repository, for its strong builtin sync and reconciliation feautures.
  * Object - contains fields of Object or Code (Handler) kind with unique name ~ObjectID
      * mandatory fields: name, kind
      * Data shards have _handler
      * Code shards have _code attribute
      * Handler PubSub has method listener_SOMENAME and callback_SOMENAME. The callback method of Handler is called if result of the corresponding listener method changed. Internal logic might intentionally call listener method to invoke subscribed callbacks.
      * version - used by reflectors and Router to facilitate subscriptions
  * Shard - contains specific version of ObjectID kind with unique address ~ShardID
  * Handler - Code shard that knows to execute methods for certain Object kind
  * Handlers Set - Handlers published by the same Realm
  * Reflector - Object sole purpose is to subscribe to a listener method of referenced PRIVATE Object. Has unique ReflectorID (likely amalgam of source ObjectID). On every change - new public shard (with updated version) is created, with the new result value is stored, the shard is signed and made available for external subscribers. \\ For security reasons, normal and published Shards have different location on disk.
  * Publish - procedure to create Reflector
  * Subscription - Object of kind Subscription that specifies rules to invoke methods of other Objects.
      * Subscription to Reflector: specifies ObjectID→method to call on each new version of specific ReflectorID
      * Subscription to Objects: specifies ObjectID→method to call on each new Object of kind "X" and possibly other conditions (like geo "Y", gender "G" or age range MIN/MAX) - used by [[:f1x:archtecture:attraction-proximity|Attraction/Proximity]]
  * Router - Caching/Routing/Matching Server (CRMS) - intermediate server, usually sits on internal network or at ISP
      * Router - keep track of objects its children realms are subscribed to, forwards objects. Allows Realms to register as children based on IP.
      * Cacher - cache frequently accessed objects
      * Matcher - [[:f1x:archtecture:attraction-proximity|Attraction/Proximity]] role
  * GeOLoC (or short Geo) - Plus Code of [[https://en.wikipedia.org/wiki/Open_Location_Code|Open Location Code]] standard

==== Site ====

Site is compute infrastructure that enables users to operate Object Realms. It consists of events routing server and presentation (like web server). \\  \\ Web server (presentation) functionality:

* authenticate the site user (a site normally has one user, preferably with unique domain)
  * communcate with core on objects CRUD
  * visualise and manage content in user-friendly way
  * show notifications

Events routing server performs functions below:

* Storage for shards
  * Execute methods
  * provide pserver interface for exported Shards
  * Keep track of subscribers, notify CRMS on changes
  * garbage collect "foreign" Shards that are not referenced anymore

=== Data Shard ===

Data Shard is on-disk representation of object with fields that has associated data handler (Code Shard), similarily to data and code separation in [[https://en.wikipedia.org/wiki/Object-oriented_programming|OOP]]. \\
Code Shard methods is written in [[https://en.wikipedia.org/wiki/Lua_(programming_language)|Lua]] and is executed in sandbox. API methods to read and call referenced Objects allows writing sophisticated applications.

==== Published Shards ====

Normal shards are accessible to Realm owner only. The owner might choose to publish methods of some objects using special "Reflector" objects. These also might be encrypted with public key of intended recipients, thus limiting who can see the content. \\  \\ Other option is publish whole Object, if it has "get_ahk" method, then it is published to DHT.

===== Router =====

Every Site is connected to one Router server. It discovesrs Routers by asking centralized "Router servers registry". It is publicly accessible and should be at PoP with good connectivity. The Router servers perform functions below:

* retrieve list of subscriptions from realms under its control, send back matching Objects
  * retrieve "exported" data from realms and share it to sites that request it. Cache the data.
  * receive notifications from children sites about new Shards, forward the Shards to other Routers, while prioritizing traffic

==== Publish/Subscribe ====

Frequently object want to know when something changes in other objects. To maintain encapsulation principle, this is done by "listener" methods. When other objects indicate desire to get notifications of a "listener" method, result of the method is remembered, together with list of "subscribed" object/methods. When Object wants to "notify" subscribers on a change, it invokes listener method that returns different value, thus causing methods of subscriber objects to be called.

The subscribers might then recalculate a value, compare with threshold and raise nofification to user or alter return value of their own listeners, thus "publishing" a change.

==== Attraction/Proximity ====

To discover other objects of same kind, there is [[:f1x:archtecture:attraction-proximity|]] "wandering search query" mechanism.

=== Task "match riders that go from Jerusalem to Eilat" ===

Objective: My Object "Intend to travel from Jerusalem to Eilat by car, 2 empty seats" need to find other objects "Intend to travel from Jerusalem to Eilat somehow". TBD

==== JQ queries ====

Microapps need to access data from other Memos. They can run [[https://jqlang.github.io/jq/|jq]] queries on "known" Memos:

* what is default measurement system of the owner? Imperial or standard
  * WHA? get list of neighbours who know me:
      * WHA? find Objects of kind People and have homeAt geo and have Memo of kind Subscription where (site=me and kind Memo=Message)
      * WHA? remove ones that have distance between me and homeAt more than 100 m

Stored queries (subscriptions) also use jq to find matching Memos: TBD How?

===== Security =====

For the system to be popular, users must trust the system to be able to protect their data. That means that Handlers must be trusted not to misuse data.

During setup Site owner is assigned "default" set of Handlers, that been carefully audited. He might change it or "overlay" it with other Handlers sets.

In addition to trusted Handlers set, data sharing must be permitted for each case. Initially Handler has "Unknown" security level. Once it reads from internal object, it is assumed "restricted" level, and it can not publish (write into public objects), unless permitted by Site Owner. The allowance might have a checkbox "remember this choice", thus allowing the particular combination of Handler and Object to publish.

==== Site security ====

Handlers are executed in sandbox, with access to Object fields (in the shard). Some fields are volatile, e.g. they are stored in cache area, separately from the shard. For POC we use [[https://www.php.net/manual/en/class.luasandbox.php|Lua]] for Handlers language ([[https://pypi.org/project/RestrictedPython/|RestrictedPython]] is possible).

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