States and Statecharts. Outline

Transcription

1 Outline Introduction Sttes Finite Automt Useful Fetures of FSA Sttechr t Bsics Sttechr t Exmples Conclusions

2 Introduction Gols 1. Understnd stte s n mjor modeling component 2. Review finite utomt, for ml chrcter iztion of stte 3. Understnd sttechr ts s medium for modeling sequentil behvior to the level of being ble to interpret sttechrts Copyr ight , E Robertson 2

3 Introduction Motivtion Stte is importnt in softwre engineering 1. Softwre lmost lwys utomtes ctive systems Stte is importnt in infor mtion systems: 2. Infor mtion systems rect to user s input rther thn merely storing nd retrieving infor mtion Rective systems hve stte-bsed behvior 3. Entities nd reltionships exhibit complex temporl nture (some OO methodologies ttempt to mrry ER nd sttechr t models) Copyr ight , E Robertson 3

4 Sttes Terminology Stte, ccording to Webster : stte stˆ-t n, often ttrib [ME stt, fr. OF & L; OF estt, fr. L sttus, fr. sttus, pp. of stre to stnd -- more t STAND] 1: mode or condition of being < stte of rediness> 1b: condition of mind or temperment <in highly nervous stte> 2: condition or stge in the physicl being of something <insects in the lrvl stte> <the gseous stte of wter> 2b: ny of vrious conditions chrcterized by definite quntities (s of energy, ngulr momentum, or mgnetic moment) in which n tomic system my exist 3: socil position; esp: high rnk... severl items concerning governments nd politics... Computer Science dds strong time proper ty to stte Copyr ight , E Robertson 4

5 Finite Automt Finite Stte Automton: Chrcter istics Histor iclly bsed in hrdwre er ly progrmmers hd n intuitive pprecition of this Tw o modes for FSA recognizer (or cceptor ) e.g. grep, ptter n mtching trnsducer e.g. zip, lexicl nlysis Nondeter minism FSA is only computing model which hndles nondeter minism (in trctble wy) even here there is n exponentil cost infltion indeter minism is essentil chrcter istic of GUI use Regulr expressions concise expression of FSA functionlity e.g. [0-9]*.[0-9]* rel number for mt Copyr ight , E Robertson 5

6 Finite Automt Finite Stte Automton: For ml Definition 1. finite set of sttes 2. finite set of inputs input lphbet 3. finite set of outputs output lphbet 4. next stte function (deterministic) current_stte input next_stte tble-dr iven: input A current B D stte C D 5. initil stte 6. output function (ction) Copyr ight , E Robertson 6

7 Finite Automt Grphicl Representtion of FSA Exmple from before: [0-9]*.[0-9]* rel number for mt _ Nottion: initil stte ccept stte Copyr ight , E Robertson 7

8 Useful Fetures of FSA Nondeter minism Nturl with grphicl representtion Choice of either pth to follow on receiving Copyr ight , E Robertson 8

9 Useful Fetures of FSA Finiteness Limittion FSA re finite becuse ll tht is known is the current stte, nd there re only finite number of sttes FSA model cnnot be enriched without dding lots of power dding counters nturl extension one counter complictes nondeter minism cceptor for n b n but not n b n c n two counters ny computble function Entire CPU contents is stte, but too mny possible sttes to be trctble Copyr ight , E Robertson 9

10 Useful Fetures of FSA Implictions of Finiteness Finite stte design implies tools for synthesis of implementtion limits on test cses only test until repetition Cn retin n FSA-like model by keeping unbounded store distinct from stte control treting reds from store s non-deterministic inputs Copyr ight , E Robertson 10

11 Sttechr t Bsics Sttechr ts: Motivtion Non-flt representtion modulr ity Condensed grphicl representtion voids stte blow-up Hndles event-dr iven GUI well voids myr id rrows from sme click-on References D. Hrel, On visul for mlisms, Comm ACM 31, D. Hrel et l., STATEMATE: wor king environment for the development of complex rective systems, IEEE Trns Softwre Engineering 16,4 April 1990 web pges Copyr ight , E Robertson 11

12 Sttechr t Bsics Sttechr ts: Chrcter istics Stte + trnsition model Hierrchy * uses nesting modulr ity * fcilittes pth groupings Or thogonlity * AND bbrevition Communiction between modules brodcst conditionl Copyr ight , E Robertson 12

13 Sttechr t Bsics Pth Grouping Abbrevition Copyr ight , E Robertson 13

14 Sttechr t Bsics Nesting Process A hs subprocess B reset A B C stop Onenter ing A, lso enter B; shown by On stop, exit B nd enter C On reset, A strts over Copyr ight , E Robertson 14

15 Sttechr t Bsics AND Abbrevition ccept odd number of s nd odd number of b s b b b b b b input is brodcst to both sides no trnsition if input doesn t mtch lbel out Copyr ight , E Robertson 15

16 Sttechr t Exmples User Interfce Specifiction A modl interfce for m: where buttons control wht is displyed on subfor m Student Infor mtion SID nme _q uit _e dit _s ve _P ersonl _C lsses _A id subfor m Pers C E_yes P A C P Clss E S Aid A E_no wht s missing? Copyr ight , E Robertson 16

17 Sttechr t Exmples Other Nottions Shown in isoltion A x[in Y ] H B C D E z/w Histor y ("H" t upper left): retur n to A in substte t time of exit Conditionl ("[in Y ]" t upper right): trnsition on input "x" only if in substte "Y" Brodcst ("/ w" t lower right): immeditely insert "w" into input strem Copyr ight , E Robertson 17

18 Sttechr t Exmples Digitl Wtch from Hrel s Comm. ACM pper A C B D A: mjor mode: time, lr m, etc. B: light; other opertions C: minor mode: minute, hour, etc. D: dte, specil step Hrel s sttechr t does not ctully show time chnges Copyr ight , E Robertson 18

19 Sttechr t Exmples Sttechr t for Digitl Wtch Wtch bt-in Ded bt-remove Live Po wer Updte Disply Dte bt-die Wek Min C C D D bt-wek TenMin C Hour C Month C Dy B Time A C A Alr m A-Min C A-TenMin C C A-Hour Bt-Ok Light Stopwtch Zero D[in Off ] B Reg S-On D[in On ] D B B Lp S-Off Disp Run A Chime A H L-Off B B L-On 2-min [not in Stopwtch ] Alr m-set D[in Alr m ] Disb Enb D[in Alr m ] time-hits-tm [in Enb ] D [in Chime ] Beep C-enb t-hits-hr Chime-set Ch-Dis Quiet C-beep D [in Chime ] Copyr ight , E Robertson 19

20 Sttechr t Exmples Adding Time Additionl components of Live in previous slide Note: lbels re incomplete 0 should be S_0, TS_0, M_0, etc. min should be min D [in Min ] tick 0 1 tick 2 tick tick tick tick tick tick tick tick /Tt Second Tt 0 1 Tt 2 Tt 3 Tt 4 Tt 5 Tt / min TenSecond min 0 1 min 2 min min min min min min min min /Tmin Minute et ceter Copyr ight , E Robertson 20

21 Conclusions Wht to Remember Processes, especilly ones with humn user input, hve input events which my occur in ny order Stte models re comptible with indeter minte event order Events chnge which processes in DFD re ctive Events my move up or down process hierrchy indfd Entities often hve stte (but the ER model is the wrong plce to model stte) Requirements Specifiction must show how events influence processes, whether or not sttechr t formlism is used Copyr ight , E Robertson 21

22 Conclusions ER Sttechr t Ar ticultion Between Models identify entities with stte must hve corresponding stte model Sttechr t ER stte model must mp to distinct entity (possibly subtype) coordinte entities through brodcst DFD Sttechr t processes tht effect sttes become edge lbels in sttechrts flows similr Sttechr t DFD ech edge lbel must correspond to process or flow ER DFD every entity must hve processes tht mintin it DFD ER identify entities used by ech process Copyr ight , E Robertson 22