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An Interface-Based Approach to Discovery and Composition of Web Services

This math thesis presentation explores the use of interface automata and parameterized interface automata to model and discover web services. It discusses the motivations behind component-based design and the need for formal modeling. The presentation also introduces interface automata and their operations of composition and refinement. Additionally, it proposes a new model, parameterized interface automata, to handle complex actions in web service composition.

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An Interface-Based Approach to Discovery and Composition of Web Services

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  1. An Interface-Based Approach to Discovery and Composition of Web Services M.Math Thesis Presentation Shahram Esmaeilsabzali 11 June,2004

  2. Outline • Interface Automata • Parameterized Interface Automata • Web services and Interface Models • Stateless Interfaces • Satisfiability Relation

  3. Motivation • Component-based design is becoming a prevalent paradigm for software development • Components are meant to provide: • Functionality without implementation details • Reusable software artifacts • Interoperable software artifacts • As such, appropriate formalisms can be used to model components

  4. Motivation Cont’d • Components usually expose their functionalities through their interfaces • Components can invoke other components’ methods • Often there are some valid orders of execution for methods of a component • Components may communicate through messagepassing

  5. Interface Automata (IA) • Interface automata are suitable models for modeling component-based systems prod_id prod_name in_us cnd$_price! prod_id? prod_name? in_us? us$_price! us$_price cnd$_price

  6. Example prod_id prod_name in_us cnd$_price credit_no us$_price cnd$_price! prod_id? ref_no! credit_no? cnd$_price? prod_name? err_no! us$_price! in_us? ref_no err_no cnd$_price us$_price

  7. Example prod_id prod_name in_us cnd$_price credit_no us$_price cnd$_price! prod_id? ref_no! credit_no? cnd$_price? prod_name? err_no! us$_price! in_us? err_no ref_no cnd$_price us_price prod_name credit_no in_us prod_id prod_id? ref_no! credit_no? prod_name? cnd$_price; prod_id? credit_no? prod_name? err_no! err_no ref_no

  8. IA Cont’d • IA is a model introduced by Luca De Alfaro and Thomas A. Henzinger for modeling component-basedsystems • IA is an interface model, with two key operations: • Composition: Commutative and associative operation mapping two IAs to one IA • Refinement: Checks similarity between two IAs

  9. IA is an interface Model • Interface models are concise models which: • Rely on helpful environments (are optimistic models) • Support composition and refinement • Support top-down design • f || g and f’refines f, then (f’ ||g)refines(f || g) • IAs are statefulinterface models

  10. IA Composition prod_id prod_name in_us credit_no us$_price cnd$_price cnd$_price! prod_id? ref_no! credit_no? cnd$_price? prod_name? err_no! us$_price! in_us? err_no ref_no cnd$_price us$_price

  11. IA Composition- Cont’d prod_id in_us prod_name credit_no credit_no? in_us? credit_no? in_us? prod_id? ref_no! prod_name? cnd$_price; prod_id? credit_no? prod_name? err_no! prod_name? in_us? prod_id? err_no! ref_no! credit_no? ref_no! err_no! err_no! ref_no! in_us? prod_name? prod_id? err_no ref_no

  12. IA Cont’d (helpful environment) prod_name credit_no in_us prod_id in_us? credit_no? credit_no? prod_id? ref_no! in_us? prod_name? cnd$_price; prod_id? credit_no? prod_name? err_no! err_no ref_no Environment ref_no err_no prod_name! credit_no! ref_no? err_no? in_us prod_id credit_no

  13. IA Refinement credit_no us$_price cnd$_price ref_no! Pay credit_no? cnd$_price? err_no! ref_no err_no cnd$_price account_no credit_no us$_price credit_no? ref_no! cnd$_price? GenPay account_no? ref_no

  14. IA is not descriptive enough • Actions in IA are atomic elements • Software methods/messages/functions are all complex elements consisting of atomic elements • To provide such complex elements we propose a new model

  15. Parameterized Interface Automata (PIA) credit_no us$_price cnd$_price ref_no! pay_in_cnd credit_no? cnd$_price? err_no! ref_no err_no

  16. PIA Cont’d • Each complex action either consists entirely of input/internal or output/internal actions • Each complex action maintains the sequentiality of its consisting simple elements during compositions

  17. PIA Composition prod_id prod_name in_us credit_no us$_price cnd$_price pay_in_cnd cnd$_price! prod_id? ref_no! cnd$_price? credit_no? err_no! us$_price! in_us? prod_name? ref_no err_no cnd$_price us$_price prod_name credit_no in_us prod_id pay_in_cnd prod_id? ref_no! credit_no? prod_name? cnd$_price; err_no! ref_no err_no

  18. PIA Composition- Cont’d prod_id prod_name credit_no in_us credit_no? in_us? pay_in_cnd credit_no? prod_id? ref_no! prod_name? cnd$_price; credit_no? err_no! prod_id? in_us? prod_name? err_no! ref_no! credit_no? ref_no! err_no! err_no! ref_no! in_us? prod_name? prod_id? err_no ref_no

  19. PIA vs. IA prod_name credit_no in_us prod_id pay_in_cnd prod_id? ref_no! credit_no? prod_name? cnd$_price; err_no! ref_no err_no prod_name credit_no in_us prod_id prod_id? ref_no! credit_no? prod_name? cnd$_price; prod_id? credit_no? prod_name? err_no! err_no ref_no

  20. PIA Refinement credit_no us$_price cnd$_price ref_no! pay_in_cnd Pay credit_no? cnd$_price? err_no! ref_no err_no credit_no us$_price cnd$_price account_no pay_in_cnd ref_no! credit_no? cnd$_price? account_no? GenPay cnd$_price? err_no! pay_in_cnd_acc ref_no err_no

  21. Web Services • Web service is a distributed component model over internet which operates using some standards/formats Web Services Flow Language (BPEL4WS, OWL-S, … ) Universal Description, Discovery and Integration (UDDI) Web Services Description Language (WSDL) Simple Object Access Protocol (SOAP) XML Common Internet Protocols (TCP/IP, HTTP, … )

  22. Web Services • AtomicWeb services can be defined by their input and outputmessages and the orderof those messages • CompositeWeb services consist of a set of atomic Web services which are glued through: • Workflows (sequence, choice, parallel,…) • Data flows (specifying the destination of messages)

  23. Web services and PIAs • Different workflow patterns can be simulated by PIAs • Data flows can be expressed through internal actions • Web services can exchange composite XML messages and PIAs can model those messages

  24. Web services and PIAs- cont’d

  25. Web services Discovery • Web services are meant to be published and discovered by interested parties. • How can interested parties search for their desired Web services? • The search request should be specified in an appropriate level of abstraction • Search requests should somehow be compared against the Web services

  26. Stateless interfaces • Statelessinterfaces do not specify the orderof events in a system • They are smaller models than stateful interfaces • Useful for specifying search requests in a Web service discovery system

  27. Multiple Port Dependency Interface (MPD) a d b m e c

  28. MPD Composition a d n m B A b m e c a d b A || B n e c

  29. MPD Request prod_id cnd$_price prod_name us$_price in_us A service which receives a “product name” or a “product id” and provides the price of that product in Canadian Dollar.

  30. Weak Interfaces • MPDs do not specify the order of dependency pairs • By defining “order” among dependency pairs, it is possible to specify some temporality • such partial specification of temporality is useful but makes composition non-associative • Weak interfacesdo not support associativity in composition • Enhanced port dependency interface (EPD) is a weak interface model

  31. Enhanced Port Dependency Interface (EPD) 1 a d 2 b m 1 e c 2

  32. EPD Composition 1 a d 2 b A 1 m m 1 B n e c 2 e 2 p a d 1 b A || B n p c 2

  33. EPD Requests 1 prod_id cnd$_price prod_name 1 2 us$_price in_us A service which receives a product id and provides the price of that product in Canadian Dollar. Or, it receives a product id and then arequest for US price and returns the price in US Dollar.

  34. Satisfiability Relations • Being able to specify search requests using MPD/EPD, we need a mechanism to compare requests against Web services • Satisfiability relations are defined between two interface classes and correlate instances of the two classes

  35. Satisfiability between PIA and EPD ref_no prod_id 1 prod_name 2 err_no credit_no prod_name credit_no in_us prod_id pay_in_cnd prod_name? ref_no! credit_no? prod_id? cnd_price; err_no! ref_no err_no

  36. Satisfiability Example ref_no prod_id 1 2 prod_name err_no credit_no prod_name credit_no in_us prod_id prod_id prod_name in_us credit_no us$_price cnd$_price pay_in_cnd prod_name? cnd$_price! ref_no! credit_no? prod_id? ref_no! credit_no? cnd$_price? prod_id? cnd_price; pay_in_cnd prod_name? err_no! us$_price! in_us? err_no! err_no ref_no cnd$_price us$_price ref_no err_no

  37. ref_no prod_id 1 prod_name credit_no err_no in_us prod_name credit_no in_us prod_id pay_in_cnd prod_id? ref_no! credit_no? prod_name? cnd_price; err_no! ref_no err_no Satisfiability Example credit_no ref_no prod_id 1 cnd$_price us$_price prod_name 1 1 cnd$_price err_no 2 us$_price in_us credit_no us$_price cnd$_price prod_id prod_name in_us pay_in_cnd cnd$_price! prod_id? ref_no! cnd$_price? credit_no? us$_price! in_us? prod_name? err_no! ref_no err_no cnd$_price us$_price

  38. Request Decomposition 1 1 prod_id prod_id cnd$_price cnd$_price cnd$_price 1 1 prod_name prod_name prod_id prod_name prod_name prod_id prod_id? cnd$_price! cnd$_price! cnd$_price! prod_id? prod_name? prod_name? cnd$_price cnd$_price cnd$_price

  39. Semantic matching • Search request and Web services may use slightly different vocabularies for inputs and outputs. Semantic matching can be helpful in this respect. ISBN ref_no 1 2 book_name err_no credit_no prod_name prod_id credit_no in_us pay_in_cnd ref_no! credit_no? prod_id? cnd_price; prod_name? err_no! ref_no err_no

  40. Future Works • Behavioral satisfaction (pre-conditions and post-conditions) • Useful decomposition techniques for interface models • Smart composition algorithm for satisfying search requests • Satisfiability relation/algorithm which uses complex actions as well as simple action • Semantic matching of messages

  41. ?

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