Chapter 4

Winter 2007 SEG2101 Chapter 4 1

Chapter 4

SDL – Structure and Behavior


Contents

• SDL – CCITT Specification and Description Language

• Nested blocks• Process• Innermost block with processes• Process behavior• Substructure• Services• SDL symbol summary


4.1: SDL (Specification and Description Language)

• Purpose and scope• Basic ideas of SDL

http://www.telelogic.com/products/tau/languages/sdl.cfm


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.


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.


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.


Basic Ideas of SDL (II)• Blocks and channels may be decomposed

into blocks and channels recursively until basic components, processes, are reached.


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.


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


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


System LevelThe first issue is to decide where to draw the system boundary.


Block

Blocks are system components and are connected by channel.


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.


System

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


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.


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


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.


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.


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.


Sketch of LocalStation


Block Type LocalStation


Correspondence between formal description and informal description


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.


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.


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.


Behavior of FSM


Description of FSM by a Process Diagram


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.


4.4: Innermost Block with Processes

• The leaves of the block structure will contain processes.


Sketch of Panel


Block Panel


Process and SignalRouteProcess symbols are connected by signalroutes.


Block LSControl


4.5: Process Behavior

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

• Dynamic


Process LSControl (I)


Process LSControl (II)


Symbols of SDL Process Diagrams

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


Start and State SymbolThere is only one start symbol for a process.

*-


Input and Output Symbol


Output Destination


Comment and Asterisk Input

* means any other input than listed.


4.8: SDL Symbol Summary


SDL Symbol Summary (II)

Chapter 4

Documents

Transcript of Chapter 4