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# SERVC ORIENTED COMPUTNG CSCE 526

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This 21 page Class Notes was uploaded by Trace Mante MD on Monday October 26, 2015. The Class Notes belongs to CSCE 526 at University of South Carolina - Columbia taught by M. Huhns in Fall. Since its upload, it has received 24 views. For similar materials see /class/229566/csce-526-university-of-south-carolina-columbia in Computer Science and Engineering at University of South Carolina - Columbia.

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Date Created: 10/26/15

Formal Speci cation and Enactment Declarative representations based on logic I Contrast with procedural flow specifications Branch and join primitives Central execution engine I Capture the essence of what is required Minimally constrain the execution of services Accommodate greater efficiencies Accommodate better handling of exceptions and opportunities Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wileyi p12i Temporal Logic Based on significant events I Declarative specifications yielding procedural execu on I Maximum flexibility bring about the right events to satisfy the stated constraints I Would support a highlevel reasoner Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wileyi p22i Speci cation Syntax L1 l gt dep dep Iltltintereavinggtgt L2 dep gt seq seq V dep ltltchoicegtgt L3 seq gt bool event event o seq ltltorderinggtgt L4 bool gt 0 T I I D literals and complements mentioned in D eg Fe 2 65 I Sequences limited to pairs of events Munindar Pt Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p32i Speci cation Semantics I Universe consists of legal runs Event instances and their complements are mutually exclusive I An event instance OCCUFS at most once M1 739 ifflt3itTi M2 739 211VI2iffT I10rT 212 M3 739 I1I2iff739 I1andT I2 M4 739 I1 o I2 iff Eli 71M I1 and Tli1alfll 12 Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p42i Example Coordination Relationships Dlt 2 E v T v e o f u If both e and f occur then e precedes f u If e and f occur on 7 neither 5 nor 7 can occur on 7 So 7 must satisfy e f which means that an initial part of 7 satisfies e and the remainder satisfies f EVng V6 EVf If e happens and f does not then do 9 Typical with data updates where g restores consistency potentially violated by the success of e and the failure of f I Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wileyi p52i Scheduling I Schedule events to satisfy dependencies stated I A realized run is in each of their denotations I Scheduler state the runs it can allow Initially given by the stated dependencies Narrows down as events occur I Key requirements I Maximal set of allowed runs flexibility I Compute symbolically and modularly Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wileyi p62i Residuation E1 OeEO E2 Tei T 133 E1 E28 5 E1 E2 E4 E1VE2e E16VE2e E5 eoEe i E ife I E E6 De i D ife Q I D E7 8 o Ee i 0 if e 6 PE 6 is any event literal E8 EoEe i 0 Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p72i Example DltEvTVeof Figure 1 Scheduler states and transitions for Dlt Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p82i Distributed Scheduling I Constrain autonomy based only on dependencies I Local decisions I Place a guard on each event I When true the event can safely happen Modified as relevant events occur I Challenges I Representing them I Reasoning with them in a distributed manner Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p92i Guard Syntax L5 T gt conj conj T L6 conj gt disj disj V conj L7 disj gt bool III seq ltgt seq I event I Events are stable I Be means e has occurred I 06 means 6 has or will occur I e means 6 has not occurred yet Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p102i Guard Semantics l Universe consists of maximal runs either an event or its complement occurs M5 u E iff u 0 E M6 uikfiffElji j g kanduj 21quot M7 u c E v F iff u ik E or u ik F M8 u ik E F iff u ik E and u ik F M9 ukEoFiffEljigj gkanduiannd u j1k F M10 u k T M11 u k IE iff u high E M12 u ik EIE iff Vj k g ju ij E M13 u ic ltgtE iff 3339 k g j and u M E Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p112i GuardsforDlt EVTVef Ie I If I GbDltg fA ltVfVDT fA fVUf fVE39f f IGbDlt9 T IGbDlt9T I GbDltf IeA IEAOEVE6VEIEEltgtEVE6 Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p122i Scheduling with Guards Example I If e is attempted first I 36 2 T e executes and notifies I Notification De changes Gf ltgtE V D6 T enabling f I If f is attempted first I Gf OE V De 75 T so it waits I Notification of EIE or Ele changes Gf to T thus enabling f I 35 2 T and GT T so they can happen any time Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p132i Motivations for Formalization I Proving correctness when Guards are compiled Guards are preprocessed Events are executed and guards updated I Justifying improvements in efficiency Simplifying guards prior to execution Updating guards incrementally Skipping some steps Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p142i Formalization Sketch 1 I Evaluation strategy a function that captures I Evolution of guards Execution of events I An evaluation strategy generates a run u if I For each event 6 that occurs on u I u satisfies as current guard due to the strategy I At the index preceding e s occurrence I Generation is more abstract than execution I A true guard may involve ltgt expressions Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p152i Formalization Sketch 2 I Begin with trivial strategy Easily correct but useless I Replace with better strategies Symbolically calculate guards from dependencies Safely discard certain terms Process messages symbolically Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p162i Symbolically Calculating Guards a GD1 V D2 e 9 GD1 e V GD2 e b GD1 D2 e 9 GD1 e GD2 e C Gelooezoenei IZIelA D i1 71 n ltgt i1 i2 ltgten1 o en G 1 n ltgt 1 nif 95Z819 17 a naq e Gelooeiooenei 9 0 f GOe Q 0 g GTe Q T Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p172i Calculating Guards Example ForDlt EVTVeof I GDoe 07 V f ltgtf g 39f I GDltE T I GDlt f 05V Ele I GDlt9 T Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p182i Assimilating Messages Old G Message M New G M G1VG2 M G1MVG2M GlAGg M G1MAG2M D6 D6 T ltgte D6 or ltgte T D5 or 05 D6 or ltgt 0 D6162 D6162 T D61 62 D62 61 0r 56 7 0r 06739 0 0613962 D61 62 or ltgt 1 2 T ltgt 1 2 D62 61 or ltgt62 61 or D67 or 067 O e De 0 g D6 or ltgte T G M G otherwise Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p192i Event Classes l Flexible agent can delay or omit l Inevitable agent can delay but not omit l Immediateagent will neither delay nor mit DltEVfV f 19 Vf39 e is inevitable I T e is immediate DgzefoVef D 0 Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p202i Summary I Generic approach to describe processes and extended transactions Hides lowlevel details Combines declarative specifications and operational decision procedures I Directions Refining methodologies based on assessment of scenarios Accommodating richer heuristics for distributed evaluations Munindar P Singh amp Michael N Huhns ServiceOriented Computing Wiley 7 p212i

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