specification/html/spec_programming_model.md - openwhisk-wskdeploy - Git at Google

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 ## Programming model

 - [OpenWhisk Entities](#openWhisk-entities)
 - [Action Composition](#action-composition)
 - [Cardinality](#cardinality)

 ### OpenWhisk Entities

 OpenWhisk uses the following entities to describe its programming model:

 #### Action

 A stateless, relatively short-running function (*on the order of seconds
 or even milliseconds*) invoked as an event handler.

 #### Trigger

 The name for a class of events. Triggers represent the events (and their
 data) themselves without any concept of how they were generated.

 #### Rule

 A mapping from a Trigger to an Action which may contain simple
 conditional logic. OpenWhisk evaluates incoming events (that belong to a
 Trigger) and invokes the assigned Action (event handler).

 #### Event Source

 An Event Source is the descriptor (edge) for an Event Producer (or
 provider). It describes the Event Format(s) produced, as well as any
 configuration and subscription capabilities.

 #### Feed

 A Feed is an optional service that represents and controls the stream
 which all belong to a Trigger. A feed provides operations called **feed
 actions** which handle creating, deleting, pausing, and resuming the
 stream of events. The feed action typically interacts with external
 services which produce the events

 #### Package

 A named, shared collection of Actions and Feeds. The goal of this
 specification is to describe OpenWhisk packages and their component
 entities and resources to enable an open-ecosystem.

 *Packages are designed to be first-class entities within the OpenWhisk
 platform to be used by tooling such as catalogs (repositories),
 associated package managers, installers, etc.*

 *Note: Not all actions must belong to packages, but can exist under a
 namespace.*

 ### Action Composition

 #### Action Sequence

 An Action that is a sequenced composition of 2 or more existing Actions.
 The Action Sequence can be viewed as a named pipe where OpenWhisk can
 automatically take the output of a first Action ‘A’ in a declared
 sequence and provides it as input to the next Action ‘B’ in the sequence
 and so on until the sequence completes.

 *Note: This composition technique allows the reuse of existing action
 implementations treating them as “building blocks” for other Actions.*

 ### Cardinality

 #### Trigger to Action

 With the appropriate set of Rules, it's possible for a single Trigger
 (event) to invoke multiple Actions, or for an Action to be invoked as a
 response to events from multiple Triggers.

 ### Conceptual representation

 ![Conceptual representation of the OpenWhisk programming model](images/conceptual_programming_model.png "image showing conceptual programming model")

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	## Programming model

	- [OpenWhisk Entities](#openWhisk-entities)
	- [Action Composition](#action-composition)
	- [Cardinality](#cardinality)

	### OpenWhisk Entities

	OpenWhisk uses the following entities to describe its programming model:

	#### Action

	A stateless, relatively short-running function (*on the order of seconds
	or even milliseconds*) invoked as an event handler.

	#### Trigger

	The name for a class of events. Triggers represent the events (and their
	data) themselves without any concept of how they were generated.

	#### Rule

	A mapping from a Trigger to an Action which may contain simple
	conditional logic. OpenWhisk evaluates incoming events (that belong to a
	Trigger) and invokes the assigned Action (event handler).

	#### Event Source

	An Event Source is the descriptor (edge) for an Event Producer (or
	provider). It describes the Event Format(s) produced, as well as any
	configuration and subscription capabilities.

	#### Feed

	A Feed is an optional service that represents and controls the stream
	which all belong to a Trigger. A feed provides operations called **feed
	actions** which handle creating, deleting, pausing, and resuming the
	stream of events. The feed action typically interacts with external
	services which produce the events

	#### Package

	A named, shared collection of Actions and Feeds. The goal of this
	specification is to describe OpenWhisk packages and their component
	entities and resources to enable an open-ecosystem.

	*Packages are designed to be first-class entities within the OpenWhisk
	platform to be used by tooling such as catalogs (repositories),
	associated package managers, installers, etc.*

	*Note: Not all actions must belong to packages, but can exist under a
	namespace.*

	### Action Composition

	#### Action Sequence

	An Action that is a sequenced composition of 2 or more existing Actions.
	The Action Sequence can be viewed as a named pipe where OpenWhisk can
	automatically take the output of a first Action ‘A’ in a declared
	sequence and provides it as input to the next Action ‘B’ in the sequence
	and so on until the sequence completes.

	*Note: This composition technique allows the reuse of existing action
	implementations treating them as “building blocks” for other Actions.*

	### Cardinality

	#### Trigger to Action

	With the appropriate set of Rules, it's possible for a single Trigger
	(event) to invoke multiple Actions, or for an Action to be invoked as a
	response to events from multiple Triggers.

	### Conceptual representation

	![Conceptual representation of the OpenWhisk programming model](images/conceptual_programming_model.png "image showing conceptual programming model")

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