ROOM Concepts

This chapter gives an overview over the ROOM language elements and their textual and graphical notation. The formal ROOM grammar based on Xtext (EBNF) you can find in the eTrice repository:
http://git.eclipse.org/c/etrice/org.eclipse.etrice.git/plain/plugins/org.eclipse.etrice.core.room/src/org/eclipse/etrice/core/Room.xtext

Actors

Description

The actor is the basic structural building block for building systems with ROOM. An actor can be refined hierarchically and thus can be of arbitrarily large scope. Ports define the interface of an actor. An actor can also have a behavior usually defined by a finite state machine.

Motivation

• Actors enable the construction of hierarchical structures by composition and layering

• Actors have their own logical thread of execution

• Actors can be freely deployed

• Actors define potentially re-usable blocks

Notation

Element	Graphical Notation	Textual Notation
ActorClass		ActorClass ActorClass2 {}
ActorRef		ActorClass ActorClass1 { Structure { ActorRef ActorReference: ActorClass2 } }

Details

Actor Classes, Actor References, Ports and Bindings

An ActorClass defines the type (or blueprint) of an actor. Hierarchies are built by ActorClasses that contain ActorReferences which have another ActorClass as type. The interface of an ActorClass is always defined by Ports. The ActorClass can also contain Attributes, Operations and a finite StateMachine.

External Ports define the external interface of an actor and are defined in the Interface section of the ActorClass.

Internal Ports define the internal interface of an actor and are defined in the Structure section of the ActorClass.

Bindings connect Ports inside an ActorClass.

Let us have a look at example:

ActorClass ActorClass1 {
	Interface {
		Port port1: ProtocolClass1
		Port port4: ProtocolClass1
	}
	Structure {
		external Port port1
		conjugated Port port2: ProtocolClass1
		conjugated Port port3: ProtocolClass1
		ActorRef ActorRef_A: ActorClass2
		ActorRef ActorRef_B: ActorClass3
		Binding port2 and ActorRef_A.port5
		Binding port3 and ActorRef_B.port6
		Binding ActorRef_B.port7 and port4
		Binding ActorRef_A.port8 and ActorRef_B.port9
	}
}

• ActorClass1 contains two ActorReferences (of ActorClass2 and ActorClass3)
• port1 is an external end port. Since it connects external actors with the behavior of the ActorClass, it is defined in the Interface section as well as in the Structure section of the ActorClass.
• port2 and port3 are internal end ports and can only be connected to the ports of contained ActorReferences. Internal end ports connect the behavior of an ActorClass with its contained ActorReferences.
• port4 is a relay port and connects external Actors to contained ActorReferences. This port can not be accessed by the behavior of the ActorClass.
• port5 through port9 are ports of contained actor references. port8 and port9 can communicate without interference with the containing actor class.
• Bindings can connect ports of the actor class and its contained actor references.

Attributes

Attributes are part of the Structure of an actor class.
They can be of a PrimitiveType or a DataClass.

Example:

ActorClass ActorClass3 {
	Structure {
		Attribute attribute1: int32       // attribute of primitive type
		Attribute attribute2: DataClass1  // attribute of DataClass type
	}
}

Operations

Operations are part of the Behavior of an actor class. Arguments and return values can be of a PrimitiveType or a DataClass. Data classes can be passed by value (implicit) or by reference (ref).

Example:

ActorClass ActorClass4 {
	Behavior {
		// no arguments, no return value
		Operation operation1(): void '''
			user code
		'''
		// argument of primitive type, return value of primitive type
		Operation operation2(Param1: int32, Param2: float64): uint16 '''
			user code
		'''
		// arguments and return value by value
		Operation operation3(Param1: int32, Param2: DataClass1): DataClass1 '''
			user code
		'''
		// arguments and return value by reference except for primitive types
		Operation operation4(Param1: int32, Param2: DataClass1 ref): DataClass1 ref '''
			user code
		'''
	}
}

Protocols

Description

A ProtocolClass defines a set of incoming and outgoing Messages that can be exchanged between two ports. The exact semantics of a message is defined by the execution model.

Motivation

• Protocol classes provide a reusable interface specification for ports

• Protocol classes can optionally specify valid message exchange sequences

Notation

Protocol classes have only textual notation. The example defines a protocol class with 2 incoming and two outgoing messages. Messages can have data attached. The data can be of a primitive type (e.g. int32, float64, …) or a data class.

ProtocolClass ProtocolClass1 {
	incoming {
		Message m1(int32}
		Message m2()
	}
	outgoing {
		Message m3(DataClass1}
		Message m4()
	}
}

Ports

Description

Ports are the only interfaces of actors. A port has always a protocol assigned. Service Access Points (SAP) and Service Provision Points (SPP) are specialized ports that are used to define layering.

Motivation

• Ports decouple interface definition (protocols) from interface usage

• Ports decouple the logical interface from the transport

Notation

Class Ports

Ports that define an external interface of the actor class, are defined in the Interface. Ports that define an internal interface are defined in the Structure (e.g. internal ports).

• External end ports are defined in the Interface and in the Structure

• Internal end ports are only defined in the Structure

• Relay ports are only defined in the Interface

• End ports are always connected to the internal behavior of the ActorClass

• Replicated ports can be defined with a fixed replication factor, e.g.
  Port port18 [5]: ProtocolClass1
  or a variable replication factor, e.g.
  Port port18[*]: ProtocolClass1

• The graphical symbols of Interface ports are drawn on the border of the actor class. The graphical symbols of Structure ports are drawn inside the border of an actor class.

The table below shows all kinds of class ports with textual and graphical notation:

ActorClass ActorClass6 {
	Interface {
		Port port12: ProtocolClass1
	}
	Structure {
		external Port port12
	}
}

ActorClass ActorClass6 {
	Interface { }
	Structure {
		Port port20
	}
}

ActorClass ActorClass6 {
	Interface {
		conjugated Port port13: ProtocolClass1
	}
	Structure {
		external Port port13
	}
}

ActorClass ActorClass6 {
	Interface {}
	Structure {
		conjugated Port port21: ProtocolClass1
	}
}

ActorClass ActorClass6 {
	Interface {
		Port port10: ProtocolClass1
	}
	Structure { }
}

ActorClass ActorClass6 {
	Interface {
		conjugated Port port10: ProtocolClass1
	}
	Structure {}
}

ActorClass ActorClass6 {
	Interface {
		Port port16[3]: ProtocolClass1
	}
	Structure {
		external Port port16
	}
}

ActorClass ActorClass6 {
	Interface {}
	Structure {
		Port port16[3]: ProtocolClass1
	}
}

ActorClass ActorClass6 {
	Interface {
		conjugated Port port17[3]: ProtocolClass1
	}
	Structure {
		external Port port17
	}
}

ActorClass ActorClass6 {
	Interface { }
	Structure {
		conjugated Port port23[3]: ProtocolClass1
	}
}

ActorClass ActorClass6 {
	Interface {
		Port port18[3]: ProtocolClass1
	}
	Structure { }
}

ActorClass ActorClass6 {
	Interface {
		conjugated Port port19[3]: ProtocolClass1
	}
	Structure { }
}

Reference Ports

These symbols can only appear on the border of an actor class reference. Since the type of port is defined in the respective actor class, no textual notation for the Reference Ports exists.

The table below shows all kinds of reference ports with textual and graphical notation:

Element	Graphical Notation	Textual Notation
Reference Port		implicit
Conjugated Reference Port		implicit
Replicated Reference Port		implicit
Conjugated Replicated Reference Port		implicit

DataClass

Description

The DataClass allows the modeling of hierarchical complex data types and operations on them. The data class is the equivalent to a class in languages like Java or C++, but has less features. The content of a data class can always be sent via message between actors (defined as message data in a ProtocolClass).

Notation

Example: DataClass using PrimitiveTypes

DataClass DataClass1 {
	Attribute attribute1: int32    // attribute of primitive type
	Attribute attribute2: float32  // attribute of another primitive type

	// no arguments, no return value
	Operation operation1(): void '''
		user code
	'''
	// argument of primitive type, no return value
	Operation operation2(Param1: int32): void '''
		user code
	'''
	// argument of primitive type, return value of primitive type
	Operation operation3(Param1: int32): float64 '''
		user code
	'''
}

Example: DataClass using other DataClasses:

DataClass DataClass2 {
	Attribute attribute1: int32      // attribute of primitive type
	Attribute attribute2: DataClass1 // attribute of DataClass

	// arguments and return value by value
	Operation operation1(Param1: int32, Param2: DataClass1): DataClass1 '''
		user code
	'''
	// arguments and return value by reference except for primitive types
	Operation operation2(Param1: int32, Param2: DataClass1 ref): DataClass1 ref '''
		user code
	'''
}

Layering

Description

In addition to the actor containment hierarchies, layering provides another method to hierarchically structure a software system. Layering and actor hierarchies with port to port connections can be mixed on every level of granularity.

1. an actor class can define a Service Provision Point (SPP) to publish a specific service, defined by a protocol class

2. an actor class can define a Service Access Point (SAP) if it needs a service, defined by a protocol class

3. for a given actor hierarchy, a LayerConnection defines which SAP will be satisfied by (connected to) which SPP

Notation

For the graphical and textual notation refer to the following table:

ActorClass Mode1 {
	Structure {
		ActorRef Services: ServiceLayer
		ActorRef Application: ApplicationLayer
		
		LayerConnection ref Application satisfied_by Services.timer
		LayerConnection ref Application satisfied_by Services.digitalIO
	}
}

ActorClass ServiceLayer {
	Interface {
		SPP timer: TimerProtocol
		SPP digitalIO: DigitalIOProtocol
	}
	Structure {
		ActorRef Timer: TimerService
		ActorRef DigIO: DifitalIOService
		LayerConnection relay_sap timer satisfied_by Timer.timer
		LayerConnection relay_sap digitalIO satisfied_by DigIO.digitalIO
	}
}

ActorClass ApplicationLayer {
	Structure {
		ActorRef function1: A
		ActorRef function2: B
		ActorRef function3: C
		ActorRef function4: D
	}
}

ActorClass A {
	Structure {
		SAP timerSAP: TimerProtocol
	}
}

ActorClass B {
	Structure {
		SAP timerSAP: TimerProtocol
		SAP digitalSAP: DigitalIOProtocol
	}
}

Finite State Machines

Description

Definition from Wikipedia:

A finite-state machine (FSM) or finite-state automaton (plural: automata), or simply a state machine, is a mathematical model used to design computer programs and digital logic circuits. It is conceived as an abstract machine that can be in one of a finite number of states. The machine is in only one state at a time; the state it is in at any given time is called the current state. It can change from one state to another when initiated by a triggering event or condition, this is called a transition. A particular FSM is defined by a list of the possible states it can transition to from each state, and the triggering condition for each transition.

In ROOM each actor class can implement its behavior using a state machine. Events occurring at the end ports of an actor will be forwarded to and processed by the state machine. Events possibly trigger state transitions.

Motivation

For event driven systems a finite state machine is ideal for processing the stream of events. Typically during processing new events are produced which are sent to peer actors.

We distinguish flat and hierarchical state machines.

Semantics

State machine execution begins at the top level by traversal of the initial transition. During traversal of a transition its (optional) action code is executed.

So called triggered transitions start at a state or a transition point. The simple most trigger is a pair of port (or SAP) and message.

For the following we will discuss hierarchical finite state machines, which include flat state machines as a special case.

Assume the state machine is in an arbitrary leaf state (states with no nested state machines). Then when an event occurs, a transition with a matching trigger is searched. This is done level by level from the state graph of the current state to the top level state graph. First all outgoing transitions are considered, then handler transitions. If no match was found this is repeated one level higher and so on to the top level. If no match is found at all, the event is discarded.

Then the transition which was triggered is traversed.

For any transition it can continue in several ways:

• If it starts from a state or is a continuation after an entry or exit point
  • and ends at a leaf state, the state machine will assume this state
  • and ends at a state with sub graph, it is called a transition to history and the last active state inside the target state is assumed
  • and ends at a choice point, the choice point branch conditions are evaluated (in arbitrary order). The first transition whose condition is met will be traversed or else the default branch is taken
• if it starts in a transition point, then in any case the current state is left, thereby executing all exit codes until the level of the transition point
  • and ends in the same transition point then the transition is traversed and the current state is activated again, thereby executing all entry codes
  • else the transition is traversed and processing continues
  • eTrice specific variant (not contained in ROOM): the transition point can be a handler. In this case no entry and exit codes of states are executed
• if the transition ends in an entry or exit point the traversal is continued on the other side of this point, entering or leaving the subgraph resp.

All this is looped until the new leaf state is reached.

Notation

We distinguish flat finite state machines (with just one level of hierarchy) and hierarchical ones.

Flat Finite State Machine

The simpler flat finite state machines are composed of the elements shown following table:

State SomeState

TransitionPoint tp

ChoicePoint cp

Transition init: initial -> Initial { }

Transition tr0: initial -> DoingThis {
	triggers {
		<doThis: fct>
	}
}

Hierarchical Finite State Machine

The hierarchical finite state machine adds the notion of a sub state machine nested in a state. A few modeling elements listed in table below are added to the set listed above.

State Running {
	subgraph {
		Transition init: initial -> Process {}
		State Process
	}
}

EntryPoint reInit

ExitPoint tp0

Examples