Seminar on Component-based Software Engineering

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Seminar on Component-based Software Engineering

• Component Coordination
• Nadia Ramjiawan
• LIACS - Leiden
  University
• Fall 2005

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Component

• Every component instance contains one or more
  active entities (thread of control).
• The active entities inside a component C can
  communicate with the active entities in other
  components only through I/O operations performed
  on the channel ends connected to C.

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Channels

• The only primitive medium of communication
  between two components.
• A channel has exactly two ends.
• A channel end is either
• Source accepts data into its channel.
• Sink dispenses data out of its channel.
• Example
• ab represents the channel with source end a and
  sink end b.
• Although every channel has exactly two ends,
  these ends can be of the same or different types
  (two sources, two sinks, or one source and one
  sink).
• Various kinds of channel are possible, offering
  different synchronisation, buffering, lossy and
  even directionality policies.
• Channel I/O Operations
• Read/write data items from /to their channel
  ends.

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Abstract Behavior Type (ABT) Model

• An ABT defines an abstract behavior as a relation
  among a set of timed-data-streams, without
  specifying any detail about
• the operations that may be used to implement such
  behavior
• or the data types it may manipulate for its
  realization.
• A timed data stream is a twin pair of streams
  consisting of a data stream and a time
  stream with the interpretation that ?i0, the
  data item appears at its corresponding
  time moment
• Used to model the data flow through channel ends.

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ABT Examples

• Basic channels
• Synchronous channel
• Asynchronous unbounded FIFO channel
• Asynchronous FIFO channel with the bounded
  capacity of 1

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ABT Examples (II)

• Asynchronous FIFO channel with the bounded
  capacity of 1 and initially contain the data item
  D
• Synchronous drain channel
• Two source ends, cannot produce any data items.
• Every data item is lost

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Merge and Replicate

• The merger ABT is defined as
• The replicator ABT is defined as

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Reo

• The ABT model is too low level to provide
  non-trivial coordination, an effective exogenous
  coordination model is needed.
• Reo is a channel-based exogenous coordination
  model wherein complex coordinators, called
  connectors are compositionally built of simpler
  ones.
• The simplest connectors in Reo are channels.
• A connector is a set of channel ends and their
  connecting channels organized in a graph of nodes
  and edges(channels) such that
• Zero or more channel ends coincide on every node.
• Every channel end coincides on exactly one node.
• There is an edge between two nodes if and only if
  there is a channel one end of which coincids on
  each of those nodes.
• Powerful mechanism for connector construction
  channel composition.

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Nodes

• Reo defines three types of nodes
• Source nodes Src(N) ? ø ? Snk(N) ø
• Src(N) and Snk(N) sets of source and sink
  channel ends coincide on N, respectively.
• A source node replicates every data item written
  to it as soon as all of its coincident source
  channel ends can consume that data item
• Sink nodes Src(N) ø ? Snk(N) ? ø
• non-deterministically selects one of the data
  items available through its coincident sink
  channel ends
• Mixed nodes Src(N) ? ø ? Snk(N) ? ø
• Combines the behavior of a sink node and a source
  node.
• Every time a data item is available through its
  coincident sink channel ends it
  non-deterministically selects an appropriate data
  item and replicates that data item into all of
  its coincident source channel ends.

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Nodes (II)

• Node I/O operations
• read and take can be done only on sink nodes
• write can be done on source nodes
• They can not be done on mixed nodes
• A component can write to a source node and read
  from a sink node only if it is connected to that
  node
• Components dont read from or write to mixed
  nodes.

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Examples of connectors in Reo

• Write-Cue Regulator
• Channels ab and cd are of type Sync and ef is of
  type Syncdrain
• Barrier Synchronizer
• The four channels ab, cd, gh, ij are all of type
  Sync and ef is of type Syncdrain
• Can be extended trivially

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Example of connectors in Reo (II)

• Ordering
• The channels ab and ac are Syncdrain and Sync,
  respectively and bc is of type FIFO1.
• Coordination pattern c (ab)
• Sequencer
• The enclosing box represents the fact that the
  details of this connector are abstracted away
  the topology inside the box is immutable
• Inside the connector, four Sync, a FIFO1(o), and
  three FIFO1 channels are connected together.

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Utility of the Sequencer

• Two-node sequencer
• Coordination pattern c (ab)
• Three-node sequencer
• Coordination pattern c (aab)

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Questions

• ?