Connector Roles and Types I

Connector Roles

Connector services can be grouped into four main classes.

Connector Types

The lecture identifies eight main connector types:

• Procedure Call
• Event
• Data Access
• Linkage
• Stream
• Arbitrator
• Adaptor
• Distributor

Procedure Call Connectors

Procedure call connectors support interaction through procedure or method calls.

They are mainly coordination connectors.

Procedure Call Dimensions

Parameters

Define how information is passed during a procedure call.

• Data transfer Data can be passed by reference, value, or using default values.
• Semantics Parameters can use different parameter-passing conventions.
• Return values Define how results are returned.
• Invocation record Describes how invocation information is handled.

Entry Point

Defines how the called component is accessed.

• Single One entry point.
• Multiple Multiple possible entry points.

Invocation

Describes how the procedure or method is invoked.

• Explicit The caller directly invokes the operation.
• Implicit Invocation can occur indirectly through mechanisms such as exceptions, callbacks, or delegation.

Procedure Synchronicity

Defines whether the caller waits for the called operation.

• Synchronous The caller waits for completion.
• Asynchronous The caller can continue without waiting.

Procedure Cardinality

Defines how many participants can be involved in the interaction.

• Fan-in Multiple sources communicate with one destination.
• Fan-out One source communicates with multiple destinations.

Accessibility

Defines who or what can access the procedure.

• Private
• Protected
• Public

Event Connectors

Event connectors support interaction through events.

They are mainly coordination connectors.

Event Connector Dimensions

Event Cardinality

Describes the number and type of participants involved in an event.

• Producers Components that generate events.
• Observers Components that receive or observe events.
• Event patterns Rules or patterns describing event interactions.

Delivery

Defines how reliably an event is delivered.

• Best effort Delivery is attempted without a strict guarantee.
• Exactly once The event is delivered exactly one time.
• At most once The event is delivered zero or one time.
• At least once The event may be delivered one or more times.

Priority

Defines the priority associated with events.

• Outgoing Priority assigned when sending an event.
• Incoming Priority considered when receiving an event.

Event Synchronicity

Defines how event processing occurs.

• Synchronous
• Asynchronous
• Timeout synchronous

Notification

Defines how components are informed about events.

Examples include:

• Polled
• Publish/subscribe
• Central update
• Queued dispatch

Causality

Defines the relationship between events and their effects.

• Absolute
• Relative

Mode

Describes the source or mechanism through which an event occurs.

• Hardware For example, page faults, interrupts, and traps.
• Software For example, signals, GUI input/output, and triggers.

Data Access Connectors

Data access connectors mainly provide communication services.

They support access to data.

Data Access Connector Dimensions

Locality

Defines where the data is located.

Examples include:

• Thread-specific
• Process-specific
• Global

Access

Defines how the data can be accessed.

Examples include:

• Accessor
• Mutator

Availability

Defines how the data is made available.

Transient Data

Data exists temporarily during execution.

Examples include:

• Registers
• Cache
• DMA
• Heap
• Stack

Persistent Data

Data remains available beyond a particular execution.

Examples include:

• Repository access
• File I/O
• Dynamic data exchange
• Database access

Data Accessibility

Defines who can access the data.

• Private
• Protected
• Public

Lifecycle

Defines how the data is managed throughout its lifetime.

• Initialization
• Termination

Data Cardinality

Defines the relationship between components and the data.

• Defines
• Uses

Linkage Connectors

Linkage connectors provide facilitation services.

They are used by higher-order connectors to enforce:

• Interconnection units
• Relationship syntax
• Interaction semantics

Linkage Connector Dimensions

Reference

Defines how connected elements are referenced.

• Implicit
• Explicit

Granularity

Defines the level at which the connection is established.

• Unit
• Syntactic
• Semantic

The connection may be based on a variable, procedure, function, constant, or type.

Linkage Cardinality

Describes the relationship between connected elements.

• Defines
• Uses
• Provides
• Requires

Binding

Defines when the connection is established.

• Compile-time
• Run-time
• Pre-compile-time