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CSI5118 W2001

CSI5118 W2001. Outline Review Verification & Validation Introduction to EFSM Models Introduction to SDL e.g. EggTimer Principles of Validation & Verification. EFSM Models. Extended Finite State Machines Same as FSM’s Enhanced features on transitions no inputs (spontaneous transitions)

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CSI5118 W2001

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  1. CSI5118 W2001 • Outline • Review Verification & Validation • Introduction to EFSM Models • Introduction to SDL • e.g. EggTimer • Principles of Validation & Verification

  2. EFSM Models • Extended Finite State Machines • Same as FSM’s • Enhanced features on transitions • no inputs (spontaneous transitions) • supports variables • guards (or conditions) • several outputs • input/output parameter support (data)

  3. FSM Models • Example (FSM) Tabular Form: Each table entry shows what symbol is output, and which new state is to be adopted Input State x y s0 0,s1 1,s0 s1 1,s1 1,s2 s2 1,s0 0,s1 y/1 0 Graph Form: The label “x/0” means that “when x is the input, 0 is the output.” x/0 x/1 y/0 x/1 1 2 y/1

  4. EFSM ModelFax Machine Example -/TOK i/RDY to/TIME I R s/ERR d, g/DLNG, PAGE to/TIME d, g, f/DLNG, ERR s/ERR Notation Used Status = {I,R,T,E} I = Idle R = Ready to Transmit T = Transmitting E = Error E T f/ERR i/PAGE Input events = {I,d,g,s,to,f} i = insert page d = dial destination number g = press “Go” button s = press “Stop” button to = timeout (5 seconds elapsed) f = failure of the attempted or pending action Output Responses = {TOK, TIME, PAGE, DLNG, ERR, RDY} TOK = “Transmission Ok” TIME = (Time of day) PAGE = “Transmitting page” DLNG = “Dialing” ERR = “Error” RDY = “Document Ready”

  5. EFSM ModelFax Machine Example -/TOK i/RDY to/TIME I R s/ERR d, g/DLNG, PAGE to/TIME d, g, f/DLNG, ERR s/ERR E T f/ERR i/PAGE • Or • ... • Transition n (d,g,f/DLNG, ERR) • FROM: ‘R’ • WHEN: ‘d’ then ‘g’ then ‘f’ • ACTIONS: ‘DLNG’ then ‘ERR’ • TO: ‘E’ • ...

  6. EFSM Model with Variables Partial Model of a Stack pop pop Empty Normal push push push push pop FSM Full Empty Normal [SC>1] push (SS=1) [SS+1=SC] push (SS=SC) [SS+1<SC] push (SS=SS+1) [SC=1] push (SS=1) Full EFSM As an exercise, do the ‘pop’ interaction for this EFSM SC = Stack Capacity SS = Stack Size

  7. SDL • Specification and Description Language • Initially built for communicating systems • Divides the specification in • Environment • System(s) The Environment Border

  8. SDL • A Whole system Block System Process Procedure

  9. Inside an SDL System Channel (and channel name) System name Signals (Messages) Declarations Signalist (set of messages) Newtype definitions

  10. SDL System Structure Signallists are declared like signals, but enclosed in parenthesis Environment of the system Channel name System blocks Signals are shown in square brackets, separated by a comma

  11. The EggTimer SDL Block Connection points (system channel names) Signals routes Procedure declaration Process declarations General declarations (signals, types, vars)

  12. The EggTimer SDL Block Structure Displayingsends to the environment and receives from Timing etc... Processes At least 1 instance and at most 1 instance of this process Procedure Reference

  13. SDL Process example Initial state Initial transition Declarations State Input Procedure call Timer Input (or timeout) Output If Task

  14. SDL Declaration example To say your declaring something Identifier (instance name) Instance type Timer declaration Initialization Timer Identifier

  15. SDL Transition example FROM WHEN ACTIONS SEND TO Local variable Parameters to send

  16. SDL Tasks Setting the timer Incrementing or attributing a value Making a procedure call Set([NOW+]<Duration>, <TimerName>) <variable> := <expression>[; <another task]

  17. SDL Procedures(and operators) Formal Parameters Procedure Start Param modifier name and type If first ‘seconds’ digit is 0 then go down, else go left Procedure return Modifiers: IN - Parameter is an Input parameter OUT - Parameter is an Output parameter IN/OUT - Parameter is both IN and OUT

  18. SDL Message Handling • Each process • has one and only one message queue • sends (by default) a message to the closest receiver (if the process itself is capable of receiving such message, it will send to itself) • the default sending procedure can be modified by • VIA: • TO: <Message_name> VIA <channel_name> <Message_name> TO <process_id>

  19. SDL Message Handling • This process queue has four possible messages • IncMinute • StartTimer • ResetTimer • OneSecond • The first three are external messages where OneSecond is an internal message, indicating when the clock has decreased one second. • There could be several other messages coming • from other processes or other blocks

  20. Principles of Validation i) Design • User-centred view • scenarios • use-cases • MSCs • functional, blackbox, providing a service (or NOT), end to end • guided execution in SDL high-level design • refined design, re-run validation scenarios

  21. SDL Guided execution • Using the Navigator in a SDL Validator tool. Up 1 Next 1: Signal: OneMinuteBtn Next 2: Signal: StartBtn Next 2: Signal: ResetStopBtn ... Next 1: Tr. Start Next i: Tr. Start By clicking on the Next, we go deriving a scenario by following the state-space tree Next 1: ... Input: DisplayTime Sender: Timing:1 Parameter(s):1,0,0

  22. SDL Guided Execution(in MSC form)

  23. Functional MSC for the previous EggTimer scenario And executing this MSC in the Validator Tool, by clicking on “Verify MSC” and selecting the proper file, we obtain (as the system has been correctly specified) 1 report 1 MSC Verification MSC ValidatorTrace verified Depth: 7

  24. Principles of Validation ii) Test • functional user interface tests in TTCN S1 Test Name Event a Event b pass c a a + b b S2 S3 Tree and Tabular Combined Notation • TTCN standard for formal test case descriptions • Facilitate sharing of tests • Eliminates Ambiguities • UNIX-based TTCN Workbench toolkit • TTCN used for X.25, ISDN, CCS7, and many other protocols • All PDU parameters specified • All tests are formally assigned verdicts

  25. Principles of Validation ii) Test (cont’d) • basic syntax & semantics of TTCN • TREE and TABLE Combined Notation Test Case Dynamic Behaviour Test Case Name: Group: Purpose: Default: Behavior Constr. Ver Label Description Reference dict Remarks A!X A?Y A!J A?K Pass A?Z Fail Wrong Resp. A?Otherwise Inc. Test body not reached Extended Comments:

  26. Principles of Verification i) Design • State-space search Process Chart Transition Chart State Space -transitions reduced state space

  27. Principles of Verification i) Design (cont’d) • Possible outcomes • Unspecified reception • queue overflow • deadlock • infinite livelock (no real progress) • Random walk

  28. Principles of Verification ii) Test • Conformance Testing (TTCN) • preamble • test step • verification sequence • postamble

  29. Principles of Verification Structure of a Transition Test Case for Conformance Testing PREAMBLE: Initialization to Preamble State TEST BODY: Application of Test Stimulus and Confirmation of System Response VERIFICATION: Confirmation of Post-Transition State POSTAMBLE: Reset to Stable State for Next Test

  30. Principles of Verification a/X Represent b/Y S1 S3 S4 As a sequence of user actions and system responses, starting in state 1 and finishing in state 4. In TTCN +Preamble(S1) !a ?X !b ?Y +Verify(S4) PASS * FAIL * Inconclusive

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