Specification and Description Language

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COUSE OF SOFTWARE ENGINEERING II AA 2001/02
Specification and Description Language
Luigi Bozzo
May 2002
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Summary

• What is SDL
• Intro
• History
• Goal
• SDL Characteristics
• SDL Structure
• Example La lotteria algebrica
• Glossary
• References

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What is SDL

• SDL (Specification and Description Language) is
  an object-oriented, formal language developed and
  standardized by The International
  Telecommunication Standardization Sector (ITU-T)
• Intended for the specification of complex,
• event-driven, real-time, and interactive
  application involving many concurrent activities
  that communicate using discrete signals

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What is SDL

• SDL describe the architecture, behaviour and data
  of distributed systems in realtime environments
• Useful for specifying the normative requirements
  of telecommunications protocol standards
• Wide spectrum language - specification to
  implementation

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History

• 1968 ITU study of stored program control
  systems
• 1972 Start of the development
• 1976 First pre-release
• 1980-1984
• Graphics, process semantics, structure, data,
• definition more rigorous, start of tools, user
  guide
• 1988 SDL88, the first standard

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History

• 1992 SDL92, MSC
• intro of OO and methodology guidelines
• 1995 SDL with ASN.1
• 1999 SDL-2000 MSC-2000
• Object modelling support
• Improved implementation support
• 2001 SDL-2001 Meeting UML

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Application area

• Type of systems
• Type of information
• Level of abstraction

• Real time
• Interactive
• Distributed
• Heterogeneous

• Behavior, structure

• Overview to details

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Use of SDL
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Goals

• Provide a better way to describe behaviour
• Support human communication and understanding
• Easy verification conformance of implementation
  of specifications
• Design optimization
• Analyzing specifications for completeness and
  correctness

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Goals

• Use of computer based tools to create, maintain
  and analyze specifications
• Formal high quality descriptions produced better,
  quicker and cheaper
• Provide to programmers an easy way to do
  verification, validation of the design,
  regression testing, automatic documentation and
  simplified maintenance

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SDL Characteristics

• Graphical form
• Based on communicating processes
• OO description of components
• Nonproprietary internationally standardized
  language
• Formality and clarity
• High degree of testability
• Portable, scalable, open, reusable

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Examples

• Cellular phones
• Switches
• GPRS
• UMTS
• GSM
• ISDN

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SDL others languages

• SDL is well suited to be the core of full-scale
  projects because of its abilities to interface
  with other languages.

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SDL Structure

• Comprises four main hierarchical levels
• System
• Block
• Process
• Procedure

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SDL Structure

• A system contains one or more blocks,
  interconnected with each other and with the
  boundary of the system by channels
• The block is the main structuring concept
• A block can be partitioned into sub-blocks and
  channels
• A channel is a means of conveying signals

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SDL Structure

• Repeated block partitioning result in a block
  tree structure
• Partitioned blocks do not contain any process

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SDL Structure

• Leaf-blocks of a block tree structure are not
  partitioned, and contain only process

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System

• The system description constitutes the top level
  of detail
• The system is what the SDL description specifies
• an abstract machine communicating with its
  environment

Environment
System
Channel
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System

• A system diagram usually contains the following
  elements
• system name
• signal descriptions
• channel descriptions
• data type descriptions
• block descriptions

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1
5
2
3
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Block

• A block is a part of the system that can be
  treated as a self-contained object

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Block

• A block diagram usually contains the following
  elements
• block name
• signal descriptions
• signal route descriptions
• channel-to-route connections
• process descriptions

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1
2
3
4
5
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Process

• A process in SDL is an extended finite state
  machine
• The behaviour of a finite state machine is
  described by states and transitions
• A process description is given through a process
  diagram
• In SDL there are five basic constructs for the
  description of a process

task
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Process

• A process diagram usually contains the following
  elements
• Process name
• Formal parameters
• Variable descriptions
• Process graph
• Procedure Descriptions
• Timer descriptions

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Process Example
Process P
1
FPAR v1 Integer
2
5
dcl c character procedure proc
Proc
3
c
4
c
Proc
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Procedure

• The procedure construct in SDL is similar to the
  one known from programming languages
• A procedure is a finite state machine within a
  process. It is created when a procedure call is
  interpreted, and it dies when it terminates
• A procedure description is similar to a process
  description, with some exceptions.
• The start symbol is replaced by the procedure
  start symbol

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Procedure

• A return symbol is introduced

• When a procedure is running, the calling process
  or procedure is suspended in the transition
  containing the procedure call

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Describing behavior with SDL

• The behaviour of a system is constituted by the
  combined behaviour of the processes in the system
• A process is defined as finite state machine,
  that works autonomously and concurrently with
  other processes
• A process reacts to external stimuli in
  accordance with its description
• A process is either in a state waiting, or
  performs a transition between two states

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Describing behavior with SDL

• The co-operation between the processes is
  performed asynchronously by discrete messages
  called signals
• Every process has an infinite input queue
  associated, which acts like a FIFO queue
• Any signal arriving at the process is put into
  its input queue

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Describing behavior with SDL

• When a signal has initiated a transition, it is
  removed from the input queue

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Process Addressing

• Every process has a unique address
• The address is not determined by the user, but is
  rather created by some abstract SDL machine
  during the creation of a process
• For any signal sent by a process there must be
  one and only one destination
• Destination can be specified
• Implicitly
• explicitly

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Explicit Addressing

• SDL has the TO construct for the explicit
  addressing of processes
• The keyword TO is used in an output, and it is
  followed by an expression containing the address
  of the destination process

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Implicit Addressing

• The explicit specification of a destination
  address is not necessary if the destination is
  uniquely defined by the system structure

A
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Process Creation/Termination

• Processes can be created by other processes
  dynamically at interpretation time
• This is indicated in a block diagram by a dashed
  line from the creating process to the created
  process
• The creating and created process must belong to
  the same block

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Process Creation/Termination
Process P1
Process P2
FPAR v1 Integer, v2 Boolean
S1
dcl v3 Integer
A
V3 v1 2
P2(A,true)
v3
S2
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Example La lotteria Algebrica
PostaElettronica_p
GestoreCartaCredito_p
1
1
lal_PE
lal_GCC


system L-AL
lal_GA
1
GestoreAccessi_p

lal_Direttore

lal_cliente
lal_giocatore




1
Cliente_u
Giocatore_u
Direttore_u
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Example La lotteria Algebrica
system L-AL
1(X)
signal collegami(DatiGiocatore,Codice),
collega(Integer,Integer), controlla(DatiGiocatore
, Codice), codiceOk(DatiGiocatore, Codice,
Chiave), seiCollegato(Chiave)


collega
DatiGiocatore_GCC
L-AL_Giocatore
L-AL_GA


collegami seiCollegato


controlla codiceOk
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Example La lotteria Algebrica
DatiGiocatori
Giocatore_u
GestoreAccessi_p
GestioneCollegamenti
collegami(gu,D,cod)
controlla(D,cod)
codiceOk(D,cod,ch)
collega(cod,ch)
seiCollegato(ch)
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Example La lotteria Algebrica
signal collegami(DatiGiocatore,Codice),
collega(Integer,Integer), controlla(DatiGiocatore
, Codice), codiceOk(DatiGiocatore, Codice,
Chiave), seiCollegato(Chiave)
Block GestioneCollegamenti
L-AL_Giocatore
collegami
seiCollegato
P1 (DatiGiocatore,Codice)
P2 (DatiGiocatore,Codice,Chiave)
codiceOk
controlla


collega
L-AL_GA
DatiGiocatore_GCC
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Example La lotteria Algebrica
process P1
process P2
FPAR v1 DatiGiocatore, v2 Codice
FPAR v1 DatiGiocatore, v2 Codice, v3 Chiave
collega (v2,v3)
controlla (v1,v2)
seiCollegato (v3)
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Glossary

• ASN.1
• Abstract data type
• CCITT
• Comite Consultatif International Telegraphique et
  Telephonique the former name of ITU-T
• FSM
• Finite state machine
• IDL
• Interface description language textual
  representation that enables designers to capture
  interfaces and data types of objects
• IPC
• Interprocess communication
• ITU
• International Telecommunications Union
• OMG
• Object Modeling Technique a notation for
  capturing requirements with object analysis

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Glossary

• ITU-T
• Telecommunications standardization body
• OMT
• Object Modeling Technique a notation for
  capturing requirements with object analysis
• SDL-GR
• Graphical notation for SDL
• SDL-PR
• Textual notation for SDL

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References

• SDL Forum Society http//www.sdl-forum.org
• Specification and Description Language Tutorial
• http//www.iec.org/online/tutorials/sdl/
• SDL 2001 Meeting UML
• 10th International SDL Forum
• Copenhagen, Denmark, June 2001
• Proceedings
• Rick Reed, Jeanne Reed
• Ed Springer
• Documenting Software Architecture Documenting
  Behavior
• http//www.sei.cmu.edu/publications/documents/02.r
  eports/02tn001.html
• Bachmann, Bass, Clements, Garlan, Ivers, Little,
  Nord, Stafford

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References

• SAM work shop
• SDL MSC workshop (open discussion platform)
• http//www.irisa.fr/manifestations/2000/sam2000/p
  apers.html

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The End
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ITU-T

• The International Telecommunication Union (ITU)
  is the United Nations specialized agency in the
  field of telecommunications
• The ITU Telecommunication Standardization Sector
• (ITU-T) is a permanent organ of ITU
• ITU-T is responsible for studying technical,
  operating and tariff questions and issuing
  Recommendations on them with a view to
  standardizing telecommunications on a worldwide
  basis

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SDL UML

• UML is a language that is good at describing
  classes/types and relationships between them in a
  simple and intuitive manner
• It does a good job in the early phases of the
  development process but in the implementation
  phases it lacks in structural behavioral
  constructs

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SDL UML

• SDL is more coherent than UML and also has a
  sound semantics foundation but is less expressive
  and widely accepted than UML
• However, SDL is strong exactly where UML is weak.
• Combining SDL with UML provides a modelling
  paradigm for visual software engineering that is
  more robust and effective than either language
  alone

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SDL UML
SDL bridges the gap between UML modeling and the
target implementation
Requirements analysis System specification
Design
Implementation
Target
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SDL UML
Convergence of UML and SDL
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Why use SDL UML ?

• Standardized notation without sacrificing
  specialized model data
• Common language that can be used from product
  conception to delivery, from system to detailed
  design levels
• Reduced learning curve across projects
• Increased domain and design model reuse
• Increased customer involvement /understanding of
  problem translation to product solution

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MSC

• The Message Sequence Charts (MSC) is a trace
  language for specification and description of the
  communication behavior of communicating systems
• Shows chronological sequences of messages sent
  between different system components (entities)
  and their environment
• Well suited for presenting a complex dynamic
  behavior in a clear, unambiguous and easily
  understandable way

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MSC Features

• Formal
• Standardized
• Graphical
• Use Cases
• Simulation trace
• (through automatically generated MSC)
• Regression Testing (checking old functionality)

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MSC Example
GestoreAccessi_p
Giocatore_s
Giocatore_u
E
collegami(gu,D,cod)
controlla(D,cod)
codiceOk(D,cod,ch)
collega(ch)
seiCollegato(ch)
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ASN.1

• ASN.1 (Abstract Syntax Notation One) is the
  ISO-ITU standardized language for defining data
  types an values
• Designed for describing structured information
  that is conveyed across some interface or
  communication medium, independently from the
  transfer format
• Used in conjunction with Basic Encoding Rules
  (BER), defining the so-called transfer syntax,
  the rapresentation of values as a bit stream to
  be transmitted

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ASN.1 Features

• Formal
• Standardized
• Complete data type definition apparatus
• Constraints, class definitions and
  parametrization
• Extensibility
• Automatic encoder/decoder generation
• Automatic implementation language representation
  generation

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ASN.1 example

• PersonName 16 IMPLICIT OCTET STRING
• Person SEQUENCE
• title 1 OCTET STRING,
• name 2 PersonName,
• height 3 Height OPTIONAL,
• weight 4 INTEGER OPTIONAL
• AddressBookEntry CHOICE
• 10 Person,
• 11 Company,
• 12 Group

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TTCN

• TTCN (Tree and Tabular Combined Notation) is a
  globally adopted standard test notation for the
  specification of test cases
• In TTCN, a test case is used for testing special
  functionality such as non-termination
• The sintax is similar to conventional programming
  languages and incorporates features like
  synchronous and asynchronous communication
  mechanisms as well as dynamic parallel test
  configuration

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TTCN

• A TTCN test suite consists of four parts
• Overview part
• An index and page references of the different
  part
• Declaration part
• Declaration of PDUs with ASN.1
• Constraints part
• Describe the value that re sent or received
• Dynamic part
• Describe the actual execution behavior of test
  suite
• Contains all test cases and default table for

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TTCN Features

• Portability
• TTCN is platform independent
• Reusability
• Since an Abstract Test Suite uses only the
  external (standardized) interfaces, it is highly
  reusable
• Modularity
• Test cases can share a common set of definitions,
  and be added incrementally
• ASN.1 integration
• ASN.1 is used for representation of data (PDUs)

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TTCN Example

• Each test case or test step is a so-called
  behavior tree

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TTCN Example

• A behavior table describes the behavior tree in a
  tabular format

Test Case Dynamic Behavior Test Case Dynamic Behavior Test Case Dynamic Behavior Test Case Dynamic Behavior Test Case Dynamic Behavior
Test Case Name Basic Connect Test Case Name Basic Connect Test Case Name Basic Connect Test Case Name Basic Connect Test Case Name Basic Connect
Purpose Check that a normal Call connection can be established Purpose Check that a normal Call connection can be established Purpose Check that a normal Call connection can be established Purpose Check that a normal Call connection can be established Purpose Check that a normal Call connection can be established
Nr Label Behavior Description Cref V
1 L!LiftHook
2 L?DialTone
3 L!Digits CallSubsr2
4 L?CallToneL?
5 LineConnect ConnSubscr2
6 L!DropHook P
7 L?BusyTone
8 L!DropHook I
9 L?NoTone F
Detailed Comments Detailed Comments Detailed Comments Detailed Comments Detailed Comments
Verdict Pass, Inconclusive, Fail