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Description

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= A stream -Subscription- is the concept of how nodes (see -ARNodeType-) subscribe to the -PropertyStream- (either the whole stream or just part of it) in a distributed manner.0x000D0x000A0x000D0x000AThis class -Subscription- describes WHAT data is required from the -PropertyStream-.0x000D0x000AUsed in connection with -ClientUpdatePosition- which describes from WHERE (from WHEN) in the historic -PropertyStream- data is to be returned.0x000D0x000A0x000D0x000AThis class describes a single subscription element. A complete query consists of one or more instances of this class. See -IsMatch- for how a query is evaluated.0x000D0x000A0x000D0x000ASome examples of subscriptions could be:0x000D0x000A0x000D0x000A1) A -Client-, for instance -ARCAPI-, subscribing (towards -CoreDB-) to those parts of the -PropertyStream- that it needs for its functioning.0x000D0x000AAs this client receives the incoming properties (through -OutsideLocalReceiver-) they would typically be stored in a -PRich- for immediate in-memory evaluation of incoming queries to the client again.0x000D0x000A0x000D0x000A2) Subscribe to logging properties for setting up of a log-console (see -app-).0x000D0x000A0x000D0x000A3) Subscribe to whole database or part of database in different manners in order to set up load-balancing, fault-tolerance, caching and similar (see -MultipleConnectionUsage- and -Sharding- for more information).0x000D0x000A(in other words, synchronizing and coordinating between multiple AgoRapide based nodes, especially between -CoreDB- nodes.) Note how the subscription instruction itself can very well be sent over the -PropertyStream-, configuring the different nodes from a central entry point of administration.0x000D0x000A0x000D0x000ASee -SyntaxHelp-.0x000D0x000A0x000D0x000ATODO: Introduce '**' in order to signify any hierarchical level.0x000D0x000ATODO: Like +**/Heartbeat/* in order to collect all -Heartbeat- in the system, regardless of hierarchical level.0x000D0x000ASee -IsMatch- (static method) for how a query consisting of multiple instances of -Subscription- are evaluated.0x000D0x000AThis class is immutable.

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