SDL

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Chapter 4

• SDL Structure and Behavior

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Contents

• SDL CCITT Specification and Description
  Language
• Nested blocks
• Process
• Innermost block with processes
• Process behavior
• Substructure
• Services
• SDL symbol summary

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4.1 SDL (Specification and Description Language)

• Purpose and scope
• Basic ideas of SDL

http//www.telelogic.com/products/tau/languages/sd
l.cfm
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Purposes of SDL

• To specify precisely the functional properties of
  a system to be constructed
• To describe precisely the functional properties
  of a system as it has been constructed.

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Scope of SDL

• Can be used in different phases of the system
  life cycle.
• May be applied over a range of abstraction levels
• Starting from very user-oriented, moving towards
  the very concrete and design dependent.
• Not intended as an implementation language and
  should not be used to bind the realization.
• Defined as a language and not a methodology.

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Basic Ideas of SDL

• SDL models independent behaviors as concurrent
  processes.
• A precise and unambiguous definition of mutual
  dependency is the prime concern.
• All dependencies are modeled explicitly as
  signals interchange between the processes and
  their environments.

• The theoretical foundation is the theory of
  finite state machine.
• An SDL system and its environment are conceived
  of as a structure of blocks connected by channels.

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Basic Ideas of SDL (II)

• Blocks and channels may be decomposed into blocks
  and channels recursively until basic components,
  processes, are reached.

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Basic Ideas of SDL (III)

• Signalroutes are the connectors between
  processes.
• Processes in the system and the environment
  communicate with each other by sending signals
  through the signalroute and channels.
• There is one and only one signal input queue
  associated with each process.

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Basic Ideas of SDL (IV)
Each process consists of the input port and an
extended finite state machine.
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4.2 Nested Blocks

• SDL conceives a system as a structure of blocks
  connected by channels and such blocks may again
  be partitioned into blocks on lower levels.
• SDL systems contain concurrent processes.
• Draw diagram to explain

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System Level
The first issue is to decide where to draw the
system boundary.
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Block
Blocks are system components and are connected by
channel.
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Channel

• Channels convey signals and there may be delay on
  transfer of a signal.
• Channels connected to frame symbol represents
  connections to environment.
• Channels may also be specified to have no delay
  and the symbol is then equivalent to the signal
  route symbol, I.e. the arrow heads are at the end.

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System
System is represented by a frame symbol which
represents the boundary of the system.
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Block Type Definition

• Block type symbol indicates that there is a block
  type definition.
• Both block reference and block type reference are
  graphical shorthands for diagrams.
• The reference defines the scope of the name.

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Block Set

• All the block instances within a block set
  typically have the same relationship with its
  surroundings.
• Block set is not a reference. It designates a set
  of block instances.
• A channel connected to a block set will actually
  represent a set of channel instances.

e, C gate
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Signal Declaration

• It is necessary to declare all signals so that
  they are visible to the processes which handle
  them.
• A note is an explanatory text embraced by /
  /.
• The surrounding frame containing the textual
  declaration is called a text symbol.
• There is no limit to the numbers of text symbol
  in a diagram.

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Signallist

• A signallist is a list of signals which has been
  given a name.
• If a signallist contains other signallists, the
  signallist names will appear in parentheses.
  (Fig.4.2)
• The signals of a channel are denoted by a list of
  signals (and signallist) in brackets.

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Block Nesting

• A singular block may be seen as a block instance
  where block instance specification and block type
  definition is combined.
• Singular block instances may be specified with
  reference to a block type omitting cardinality of
  block set specification.
• Block types may contain a connectivity graph of
  block instances connected by channels.
• At leaves there are blocks which contain
  processes.
• Block type may not contain both blocks and
  processes at the same time.

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Sketch of LocalStation
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Block Type LocalStation
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Correspondence between formal description and
informal description
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Gate

• Gates are used to indicate which channels of the
  block types are supposed to connect to which
  channel connecting an instance of type.
• e and C
• Gate names are defined by the type and visible
  wherever the type name is visible.
• Gate symbols have arrows at ends and signal lists
  are associated with arrows.
• Signallists will ensure the instances of the
  block type are connected correctly to their
  surroundings.

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4.3 What is a Process?

• In SDL a process is an actor object executing his
  own actions and having his own local (data)
  attributes.
• Processes have discrete behavior.
• Processes interact by means of signals.
• Signals are discrete stimuli which are actively
  screened and processes by the receiver.

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Process

• SDL processes are described as FSMs.
• Process is closely related to behavior.
• System and block definitions concentrated on
  static relationships.
• Process descriptions concentrate on what is
  changing.
• The structure of process is what is stable when
  the process behaves.

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Behavior of FSM
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Description of FSM by a Process Diagram
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Form of Process Diagram

• In general, each state transition has the
  following form.
• In a state transition a process sits in its
  current state until an expected input event is
  received.

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4.4 Innermost Block with Processes

• The leaves of the block structure will contain
  processes.

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Sketch of Panel
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Block Panel
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Process and SignalRoute
Process symbols are connected by signalroutes.
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Block LSControl
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4.5 Process Behavior

• The SDL way of describing a finite state machine
  (FSM).
• Dynamic

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Process LSControl (I)
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Process LSControl (II)
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Symbols of SDL Process Diagrams

• A frame surrounding the process diagram page
  separates a process from its environment.

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Start and State Symbol
There is only one start symbol for a process.
-
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Input and Output Symbol
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Output Destination
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Comment and Asterisk Input
means any other input than listed.
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4.8 SDL Symbol Summary
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SDL Symbol Summary (II)