Models and Languages for Service-Oriented and Cloud Computing

Transcription

1 Models and Languages for Service-Oriented and Cloud Computing University of Bologna Gianluigi Zavattaro DISI - Department of Computer Science and Engineering INRIA research team FOCUS BISS 2016 Bertinoro 7-11 March 2016

2 A brief introduction u Associate Professor at the University of Bologna, DISI Computer Science and Engineering Department u My background: n Foundational aspects of programming languages n Concurrency theory u My recent interests (this course): n Rigorous investigation of basic concepts in emerging classes of languages for wide area programming

3 The Programmable Web The Web offers a continuosly growing number of services available through dedicated APIs

4 The Programmable Web Different kinds of APIs (with their corresponding protocols) exist

5 Service-Oriented Programming u but in general, independently from the protocols/apis, services call for: n Specific programming paradigms: w ORC: functional approach w Chor / Jolie: imperative approach n Specific programming concepts: w Behavioural interfaces, compliance, global behavioural specifications, conformance,

6 ORC u Basic idea: n Apply the functional paradigm to service-oriented programming n Incorporate in the programming language the concept of service (as a special form of function, called site) and n... define composition operators to program the so-called service orchestrations Jayadev Misra, William R. Cook: Computation Orchestration. Software and System Modeling 6(1): (2007)

7 Formal definition of ORC syntax

8 Formal definition of ORC syntax Publishes 1 or no value

9 The site in ORC u The basic ORC expression is site call n A site is invoked, as a function, but it nondeterministically publishes either one value or never return any value w No value reflects, at the programming language level, the unreliability of services n Ex: BBC(d) either returns the BBC newspage for date d, or never returns

10 Formal definition of ORC syntax Three main composition operators

11 Composition operators in ORC u ORC expression can be combined n in parallel: CNN(d) BBC(d) this expression can publish 0, 1 or 2 values n in sequence: (CNN(d) BBC(d) ) >m> ( xxx@yyy,m) each value published from the lhs activates the evaluation of the rhs (the published values are assigned to the variable m) n in asymmetric parallel (see next slide)

12 Asymmetric parallel composition u ( xxx@yyy,m) where m: (CNN(d) BBC(d) ) sends the only relative to the first newspage published by the rhs (not both!) n The lhs and rhs start to be evaluated in parallel n but the evaluation of the subexpressions of the lhs that needs m are deferred until the first value is published, and assigned to m

13 Formal definition of ORC syntax Expression definition Expression call

14 Expression definition u ( xxx@yyy,m) where m: (CNN(d) BBC(d) ) This expression can be rewritten as follows: TwoNews(d) Δ CNN(d) BBC(d) ( xxx@yyy,m) where m: TwoNews(d) n The defined expression can be used inside other expressions (by indicating actual parameters) w it is replaced by its definition, where formal parameters are replaced by the actual ones

15 Formal definition of ORC semantics

16 Formal definition of ORC semantics Asynchronous semantics: Call, Return, Publication are separated events (let is a special site that simply publishes its arguments)

17 Formal definition of ORC semantics Parallel composition

18 Formal definition of ORC semantics Sequential composition

19 Formal definition of ORC semantics Asymmetric parallel composition

20 Formal definition of ORC semantics Expression definition evaluation

21 Example ( where m: (CNN(d) BBC(d) ) à ( xxx@yyy,m) where m: (?u BBC(d) ) à ( xxx@yyy,m) where m: (?u?u ) à ( xxx@yyy,m) where m: (let(n)?u ) à ( xxx@yyy,n) à?u à let(c) à 0

22 Pros and Cons of the asynchronous semantics ( where m: let(n) ComplexExpression u In real life the will consider n n instead of the first value published by a very complex expression (e.g., including hundreds of external service invocations) u For this reason ORC has been equipped also with a synchronous semantics u The idea is to postpone responses u?c (produced by the SiteRet rule) thus giving priority to local actions n n The semantics is now divided in alternative rounds: local actions, one response, local actions, one response,. In this way, if ComplexExpression requires at least one site call, let(n) is guaranteed to publish first (during first round)

23 ORC equivalences u What about 0 and 0 >x> f? Are these expressions equivalent? u What about (g h) >x > f and (g >x > f ) (h >x > f )? u What about f >x > (g h) and (f >x >g) (f >x > h)? u What about (f >y > g) where x : h and (f where x : h) >y > g?

24 Bisimulation has been used to prove equivalence laws

25 Bisimulation has been used to prove equivalence laws

26 The ORC language u What we have seen so far is named ORC calculus u A fully fledged language, called ORC, has been developed starting from the calculus u Few examples of programs follows n An ORC interpreter is available at:

27 Basic site calls u Println is a built-in site that prints a string (and then publishes a generic signal): Println ("Hello World") u Prompt is a built-in site that prompt the user to input a string, which is then published: Prompt("What is your name?")

28 Basic composition operators u Parallel composition: Prompt("Red or black?") Prompt("Odd or even?") u Sequential composition: Prompt("What is your name?") > x > Println("Your name is " + x) u Asymmetric parallel composition: fruits < fruits < ( Prompt("Apples or oranges?") Prompt("Grapes or mangos?") )

29 Ask two questions and use both answers ( Prompt("Red or black?") Prompt("Odd or even?") ) > x > Println("Your choice is " + x)

30 Ask two questions and use both answers ( Prompt("Red or black?") Prompt("Odd or even?") ) > x > Println("Your choice is " + x) Modify it to use only the first answer

31 Ask two questions and use both answers Println("Your choice is " + x) < x < ( Prompt("Red or black?") Prompt("Odd or even?") ) here it is... only the first answer!

32 Similar ORC expressions ("Red" "Blue") > x > Println("A nice color: " + x) ( Prompt("Write Red") "Blue") > x > Println("A nice color: " + x) Println("A nice color: " + x) < x < ("Red" "Blue") Println("A nice color: " + x) < x < (Prompt("Write Red") "Blue")

33 Timer u Rwait is a special site n When invoked with parameter t, it publishes a signal after t milliseconds "immediately" Rwait(3000) >> "..three seconds later.." Rwait(5000) >> "..five seconds later.."

34 A metronome def metronomen(i) = i Rwait(1000) >> metronomen(i+1) metronomen(0) def is used for expression definitions

35 Some real Web Service u HTTP requests: def randombytes(n) = val location = " val query = {. nbytes = n, fmt = "xml".} val response = HTTP(location, query).get() val xml("hotbits", xml("random-data", data)) = ReadXML(response) data.replaceall("\\s+"," ") randombytes(4)

36 Some real Web Service u Libraries are available that use Web Services as ORC sites: include "net.inc" GoogleGeocoder("Bertinoro") Publish a list of hits include "search.inc" Google("Sangiovese") > x > each(x) Publish the single elements in a list

37 Some real Web Service u Libraries are available that expose Web Services as ORC sites: include "net.inc" val BingSpell = BingSpellFactoryPropertyFile ("orc/orchard/orchard.properties") BingSpell("beutiful bertinoro!")

38 Exercise u Ask the user for a string and then.. u.. print the spell checked version of the string, if this can be done in less than 250ms, or print the typed string

39 Exercise u Ask the user for a string and then.. u.. print the spell checked version of the string, if this can be done in less than 250ms, or print the typed string include "net.inc" val BingSpell = BingSpellFactoryPropertyFile ("orc/orchard/orchard.properties") Println(y) < y < ( Prompt("Input a string: ") > x > ( BingSpell(x) (Rwait(250) >> x) ) )

40 ORC: conclusion u ORC is an example of a language: n Specifically designed for service-oriented programming n Developed starting from a formally defined calculus n Particularly tailored for service orchestration w The orchestrator is the unique point of invocation for the other services

41 WS-BPEL u The most famous orchestration language is WS-BPEL n Web Service Business Process Execution Language: result of the effort of industries like IBM, Microsoft, ORACLE, SAP, n XML based language, including many different constructs, inherited from several predecessors of single companies in the consortium

42 Difficult XML syntax...

43 easier graphical notations u WS-BPEL has a complex XML syntax, but frontend graphic notations (similar to BPMN) have been designed