Chapter 8 Web Services Foundations

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1 Prof. Dr.-Ig. Stefa Deßloch AG Heterogee Iformatiossysteme Geb. 36, Raum 329 Tel. 0631/ Chapter 8 Web Services Foudatios

2 Outlie Service-orieted computig Motivatio & Architecture Implemetig SOAs Web Services System Architecture Overview of Techologies ad Stadards SOAP for Web Service Ivocatio Message Format Processig Model WSDL for Web Service Descriptio Mai Igrediets & Documet Structure Web Service Policies UDDI for Web Service Discovery Applicatio Developmet Prof.Dr.-Ig. Stefa Deßloch 2 Middleware for Heterogeeous ad Distributed Iformatio Systems

3 Service-Orieted Computig (SOC) Service-orieted architecture (SOA) models a applicatio as a compositio of reusable services focus is o fuctios, ot thigs (i cotrast to OO-desig) services are characterized by the messages they exchage the iterface cotracts defied betwee service requester ad provider TP system based o SOA may iclude multiple reusable services offered by a sigle TA-program, or multiple distributed services both sychroous ad asychroous commuicatio mechaisms service is ivoked by sedig a message to the service service ca implemet a TA or a step withi a TA (request cotroller or TA server) Icreased popularity of SOC service-orieted access to fuctios of large-scale web sites (search, social etworkig, e-commerce) advet of stadard web service protocols Prof.Dr.-Ig. Stefa Deßloch 3 Middleware for Heterogeeous ad Distributed Iformatio Systems

4 Types of E-Busiess Busiess To Cosumer (B2C) Busiess To Busiess (B2B) Itra Busiess Relatio betwee eterprise ad customers Sales-related aspects are predomiat, like product presetatio, advertisig, service advisory, shoppig Relatio betwee processes of differet eterprises Predomiat are relatio to suppliers, ad customer relatios to other eterprises like idustrial cosumers, retailers, baks Electroic orgaizatio of iteral busiess processes, like realizatio withi workflow systems Prof.Dr.-Ig. Stefa Deßloch 4 Middleware for Heterogeeous ad Distributed Iformatio Systems

5 B2B Itegratio - Covetioal Middleware Middleware itself is (logically) cetralized usually cotrolled by a sigle compay ow requires agreemet o usig, maagig specific middleware platform across compaies ("third party") eed to implemet a "global workflow" problems lack of trust autoomy eeds to be preserved busiess trasactios are cofidetial Poit-to-poit solutios lack of stadardizatio may parters ivolved -> heterogeeity of middleware platforms Focus o LAN isufficiet support for iteret protocols problems with firewalls caot work with multiple trust domais Prof.Dr.-Ig. Stefa Deßloch 5 Middleware for Heterogeeous ad Distributed Iformatio Systems

Service-Orieted Architecture (SOA) Service Requestor Fids required services via Service Discovery Bids to services via Service Provider Service Provider Provides e-busiess services Publishes

6 Service-Orieted Architecture (SOA) Service Requestor Fids required services via Service Discovery Bids to services via Service Provider Service Provider Provides e-busiess services Publishes availability of these services Service Discovery Service Registry Provides support for publishig ad locatig services Like telephoe yellow pages Service Idex Publicatio is "passive": service descriptios are made available ad gathered by idex service Peer-to-peer Dicovery Dyamic discovery: requestor sed queries to peers i a etwork Defiitio (give by OASIS SOA Referece Model): "A paradigm for orgaizig ad utilizig distributed capabilities that may be uder the cotrol of differet owership domais" Publish Service Discovery Service Provider Fid Bid Service Requestor Prof.Dr.-Ig. Stefa Deßloch 6 Middleware for Heterogeeous ad Distributed Iformatio Systems

7 Implemetig SOAs Implemetatio based o Web Services applicatio fuctio is mapped to a specific service iterface (e.g., AddCustomer) stadards for SOA: ivocatio (SOAP), iterface descriptio (WSDL), registry (UDDI), all based o XML iteroperability: iterfaces are available for appl. servers, ORBs, MOM, DBMS, icludes trasactio iteroperability service assembly & compositio: tools ad techiques available Implemetatio based o Represetatioal State Trasfer (REST) architectural style for buildig large-scale distributed hypermedia systems applicatio fuctio is mapped to a specific resource providig a geeric iterface resource idetificatio through URI; uiform iterface: HTTP GET, PUT, POST, DELETE example: HTTP POST o to add customer resources ecode sessio state, fuctio idetifiers ad parameters represetatioal state trasfer usig self-cotaied messages self-descriptive messages usig HTTP header (cotet-type, accept fields) resources are decoupled from their represetatio cotet ca be accessed i a variety of formats, such as JSON (cotet egotiatio) Prof.Dr.-Ig. Stefa Deßloch 7 Middleware for Heterogeeous ad Distributed Iformatio Systems

8 RESTful Web Services Web services provided purely based o the above priciples alterative to WSDL/SOAP-based big web services Ratioale perceived to be simple leverages existig, well-kow stadards (HTTP, XML, URI, MIME) light-weight ifrastructure that requires oly miimal toolig, is iexpesive similar to buildig dyamic web site REST ad Ajax (see later chapter) complemet each other icely suitable for hostig applicatios o the web Drawbacks ad limitatios (still) eeds careful desig ad eumeratio of resources to be exposed, mapped to geeric iterface, ad of data represetatios used more flexible, but more format variatios to accout for oly RPC-style iteractios, HTTP-oly requires maual implemetatio of reliability, trasactios Prof.Dr.-Ig. Stefa Deßloch 8 Middleware for Heterogeeous ad Distributed Iformatio Systems

9 Web Services Distributed computig platform built o existig ifrastructure icludig XML & HTTP Web services are for B2B what browsers are for B2C Self-cotaied, self describig, modular service that ca be published, located ad ivoked across the web Refer to ope stadards ad specificatios: compoet model (WSDL) iter-compoet commuicatio (SOAP) discovery (UDDI) Platform- ad implemetatio-idepedet access Described, searched, ad executed based o XML Eable compoet-orieted applicatios Loose couplig from cliet to service Eable to itegrate legacy systems ito the web Useful for other distributed computig frameworks such as CORBA, DCOM, EJBs è Web services as wrappers for existig IS-fuctioality Prof.Dr.-Ig. Stefa Deßloch 9 Middleware for Heterogeeous ad Distributed Iformatio Systems

10 Web Service System Architecture Commo iteral architecture leveragig covetioal middleware service provider web services iterface access to iteral systems cliet iteral web service middleware covetioal middleware other tiers other tiers Prof.Dr.-Ig. Stefa Deßloch 10 Middleware for Heterogeeous ad Distributed Iformatio Systems

11 Exteral Web Services Architecture Service Requestor exteral middleware Service Provider web services cliet trasactio maagemet trasactio maagemet web service iteral middleware other protocol ifrastructure compositio egie other protocol ifrastructure compositio egie iteral middleware other tiers other tiers service service service descriptios descriptios descriptios Directory Service Provider Prof.Dr.-Ig. Stefa Deßloch 11 Middleware for Heterogeeous ad Distributed Iformatio Systems

12 Techologies: Service Descriptio & Discovery Service Descriptio Commo Base Laguage (àxml) Iterfaces (àwsdl) exted "traditioal" IDLs iteractio mode address/trasport protocol ifo Busiess Protocols (àwscl, BPEL) describe possible coversatios order of iteractios Properties ad Sematics (àuddi, WS-Policy) descriptios to facilitate bidig i a loosely-coupled, autoomous settig e.g., o-fuctioal properties (cost, trasactioal & security support) textual descriptios orgaize this iformatio Vertical Stadards iterfaces, protocols, etc. specific to applicatio domais Service Discovery Directory/Repository for WS descriptios APIs ad protocols for directory iteractio vertical stadards properties ad sematics busiess protocols iterfaces commo base laguage at desig-time or ru-time directories Service Descriptio ad Discovery Stack Prof.Dr.-Ig. Stefa Deßloch 12 Middleware for Heterogeeous ad Distributed Iformatio Systems

13 Techologies: Service Iteractio & Compositio Service Iteractio Trasport lots of possibilities HTTP most commo Basic ad Secure Messagig stadardize how to format/package iformatio to be exchaged (àsoap) defie how to exted basic mechaism to achieve additioal capabilities (àws- Security) Protocol Ifrastructure (meta-protocols) geeral ifrastructure for busiess iteractios maitai state of coversatio meta-protocols which protocols do we use? who is coordiatig? Middleware Properties (horizotal protocols) properties similar to those of covetioal middleware reliability, trasactios, Service Compositio middleware properties protocol ifrastructure basic ad secure messagig trasport Service Iteractio Stack Implemet web service by ivokig other web services Similar to workflow maagemet, oly for web services Prof.Dr.-Ig. Stefa Deßloch 13 Middleware for Heterogeeous ad Distributed Iformatio Systems

14 SOAP Simple Object Access Protocol middleware properties protocol ifrastructure basic ad secure messagig trasport Service Iteractio Stack Defies how to format iformatio i XML so that it ca be exchaged betwee peers message format for stateless, oe-way commuicatio support loosely-coupled applicatios covetios for iteractio patters (RPC) implemet "o top of" oe-way messagig first message ecodes the call, secod (reply) message the result processig rules for SOAP messages how to trasport SOAP messages o top of HTTP, SMTP Prof.Dr.-Ig. Stefa Deßloch 14 Middleware for Heterogeeous ad Distributed Iformatio Systems

SOAP Evelope Framework Defies mechaism for idetifyig What iformatio is i the message Who should deal with the iformatio Whether this is optioal or madatory Evelope elemet is the root elemet of the

15 SOAP Evelope Framework Defies mechaism for idetifyig What iformatio is i the message Who should deal with the iformatio Whether this is optioal or madatory Evelope elemet is the root elemet of the SOAP message, cotais Optioal header elemet Madatory body elemet Body elemet Cotais arbitrary XML applicatio-specific Child elemets are called body etries (or bodies) Example: Prof.Dr.-Ig. Stefa Deßloch 15 Middleware for Heterogeeous ad Distributed Iformatio Systems

16 SOAP Headers Primary extesibility mechaism i SOAP Additioal facets ca be added to SOAP-based protocols Mechaism to provide additioal "cotrol" iformatio (e.g., directives, cotext iformatio) pass iformatio that is orthogoal to the specific iformatio to execute the request Ay umber of headers ca appear i a SOAP evelope Usage areas Applicatio-specific extesios (see previous example) e.g., reservatio idetificatio, customer idetificatio ad iformatio, Geeric service extesios autheticatio, authorizatio, trasactio maagemet, paymet processig, tracig, auditig Header cotet Arbitrary XML Determied by the schema of the header elemet Prof.Dr.-Ig. Stefa Deßloch 16 Middleware for Heterogeeous ad Distributed Iformatio Systems

17 SOAP Itermediaries SOAP itermediaries provide "value-added services" SOAP message ca travel through multiple SOAP odes Seder [-> Itermediary ] -> ultimate Receiver Itermediaries process oe or more SOAP headers Header is removed from the message after processig (default behavior) ca be reiserted by the itermediary, possibly with modified values Itermediary does ot eed to uderstad message body reservatio cliet customer id reservatio id body cust-service itermed. customer id + prefereces reservatio id body reservatio server Prof.Dr.-Ig. Stefa Deßloch 17 Middleware for Heterogeeous ad Distributed Iformatio Systems

18 SOAP-based RPCs SOAP is fudametally a stateless, oe-way message exchage paradigm but applicatios ca create more complex iteractio patters Request/respose, request/multiple resposes SOAP-based RPC Employs request/respose message exchage patter (MEP) MEPs defie "templates" for more complex message eschages Ivocatio is modeled as a struct of i/iout parameters <docheck> <product> </product> <quatity> </quatity> </docheck> Respose is modeled as a struct as well <docheckrespose> </docheckrespose> All data is passed by-value Edpoit (address of target ode) to be provided i a protocol bidig-specific maer Prof.Dr.-Ig. Stefa Deßloch 18 Middleware for Heterogeeous ad Distributed Iformatio Systems

19 More SOAP SOAP protocol bidigs SOAP is trasport-idepedet, ca be boud to ay protocol type E.g., SMTP, JMS, UDP, SOAP stadard defies a bidig to HTTP Bidig to HTTP (sychroous protocol) makes RPC-style atural Oe-way exchage will use simple ackowledgemet as HTTP respose SOAP with Attachmets XML is t good at carryig o-xml thigs withi it Itroduces a outer multipart MIME evelope Root part is SOAP evelope Other parts ca be aythig: XML, images, WS-Addressig provides a mechaism to place the target, source ad other importat address iformatio directly withi the Web service message decouples address iformatio from ay specific trasport model w3c recommedatio Prof.Dr.-Ig. Stefa Deßloch 19 Middleware for Heterogeeous ad Distributed Iformatio Systems

20 Web Services Descriptio Laguage (WSDL) Provides all iformatio ecessary to programmatically access a service documetatio for distributed systems recipe for automatig the details ivolved i applicatios commuicatio Descriptio of the logical web service iterface operatios, parameters, similar to IDL i covetioal middleware Describes mechaism to access the web service which protocol is used SOAP, service locatio WSDL stadardizatio pursued by w3c V1.1 specificatio is a w3c ote ot a official stadard, but most widely used vertical stadards protocols ad sematics busiess protocols iterfaces commo base laguage WSDL 2.0 is a w3c recommedatio Service Descriptio ad Discovery Stack directories Prof.Dr.-Ig. Stefa Deßloch 20 Middleware for Heterogeeous ad Distributed Iformatio Systems

21 Igrediets of WSDL Abstract part (typical scope of a iterface defiitio laguage) Types: Defiitios of data types eeded (e.g., message types) uses XMLSchema as a default laguage Message Exchage Patter: Abstract defiitio of data exchage defies sequece of iput ad output messages, idepedet of a specific service Operatio: Abstract actios supported by the service Iterface: Iterface defied as set of operatios Cocrete part Bidig: Cocrete protocol ad data format used to implemet a iterface E.g., SOAP/HTTP, HTTP GET/POST the same service ca be supported by multiple protocols/bidigs simultaeously Edpoit: Sigle idividual "ed poit" idetified by a etwork address supportig a particular bidig Service: Collectio of related "ed poits Group edpoits related to the same service iterface but expressed by differet protocols (bidigs) Prof.Dr.-Ig. Stefa Deßloch 21 Middleware for Heterogeeous ad Distributed Iformatio Systems

22 WSDL 2.0 Documet Structure Prof.Dr.-Ig. Stefa Deßloch 22 Middleware for Heterogeeous ad Distributed Iformatio Systems

23 Message Exchage Patters Defies iteractio paradigms exchage of several asychroous messages sequece ad cardiality of messages i a operatio abstract: o message types, o bidig-specific iformatio is specified miimal cotract Stadard MEPs defied by WSDL specificatio i-boud MEPs I-Oly, Robust I-Oly, I-Out, I-Optioal-Out out-boud MEPs Out-Oly, Robust Out-Oly, Out-I, Out-Optioal-I Where to sed to? Outside scope of WSDL Iformatio could be provided through aother (subscribe) operatio or defied at deploymet time Extesibility possible to defie ew MEPs Prof.Dr.-Ig. Stefa Deßloch 23 Middleware for Heterogeeous ad Distributed Iformatio Systems

24 Iterface Iterface is a set of abstract operatios may exted other iterfaces (i.e., multiple iterface iheritace) faults, operatios, etc. are iherited overloadig of operatios is ot supported iheritace coflicts must ot occur default style for operatios ca be specified Operatio groups a set of abstract messages ivolved refereces a MEP that defies sequece of messages defies the structure of iput, output, ifault, outfault messages by referecig the appropriate (schema) types optioally declares a style rules used for geeratig messages, e.g., RPC style or Documet style may optioally be declared "safe" Iterface Fault o further obligatios result from a ivocatio defiitio of faults that ca occur i the scope of this iterface Prof.Dr.-Ig. Stefa Deßloch 24 Middleware for Heterogeeous ad Distributed Iformatio Systems

25 Web Service Policies Web service capabilities ad requiremets eed to be described as (machiereadable) metadata examples: addressig, security, trasactios, reliability allows tools to check for service compatibility, geerate code WS-Policy express capabilities, characteristics of etities i a WS-based system policy assertios, expressios, statemets example: <All> <wsam:addressig> </wsam:addressig> <ExactlyOe> <sp:trasportbidig> </sp:trasportbidig> <sp:asymmetricbidig> </sp:asymmetricbidig> </ExactlyOe> </All> allows seders, receivers to specify their security requiremets ad capabilities WS-PolicyAttachmet associate policy expressios with subjects referece policies from WSDL defiitios or ilie them i bidigs associate policies with UDDI etities Prof.Dr.-Ig. Stefa Deßloch 25 Middleware for Heterogeeous ad Distributed Iformatio Systems

26 Uiversal Descriptio Discovery ad Itegratio (UDDI) Goal: eable service discovery catalogue services based o published iformatio of service providers maitai taxoomy(ies) to support searchig for appropriate services i busiess terms specify techical bidig iformatio to actually commuicate with the selected service UDDI registry serves as a directory of web services Allows searchig by what ad by how istead of just by ame UDDI defies Set of schemas for describig busiesses ad their services UDDI data model SOAP API for accessig a UDDI registry UDDI iitiative Ivolves more tha 300 compaies Prof.Dr.-Ig. Stefa Deßloch 26 Middleware for Heterogeeous ad Distributed Iformatio Systems

27 UDDI Core Data Structures busiessetity: iformatio about the party publishig service iformatio tmodel: descriptios of specificatios for services or value sets; basis for techical figerprits cotais 0 or more busiessservice: descriptive iformatio about a family of techical services refereces to desigate iterface specificatios for a service cotais 1 or more bidigtemplate: techical iformatio about service etry poit ad implemetatio specs UDDI key uiquely idetifies each istace of core data structures withi a registry basis for realizig the cotaimet/referecig relatioships (usig foreig keys) XML Schema defiitio for UDDI Data Model Prof.Dr.-Ig. Stefa Deßloch 27 Middleware for Heterogeeous ad Distributed Iformatio Systems

28 Registry Types Differet types of registries corporate/private (e.g., eterprise web service registry) operates withi the boudaries of a sigle compay (or for a restricted umber of parters) data is ot shared with other registries affiliated (e.g., tradig parter etwork) registry is deployed i a cotrolled eviromet limited access by authorized cliets data may be shared with other registries i a cotrolled maer public (e.g., UDDI Busiess Registry) ope, public access to registry data secured admiistrative access, cotet may be moderated data may shared, trasferred amog registries UDDI Busiess Registry public, global registry of busiesses ad their services master directory of publicly available e-commerce services was iitial focus of UDDI effort Prof.Dr.-Ig. Stefa Deßloch 28 Middleware for Heterogeeous ad Distributed Iformatio Systems

29 Applicatio Developmet UDDI publish fid geerate WSDL geerate geerate Proxy Trasport Stub Requestor Service Prof.Dr.-Ig. Stefa Deßloch 29 Middleware for Heterogeeous ad Distributed Iformatio Systems

30 Java API for XML Web Services (JAX-WS) API for buildig web services ad cliets based o remote procedure calls ad XML Goal: hide all the complexities of SOAP message processig APIs for supportig XML based RPC for the Java platform Defies Defie web service Use web service WSDL/XML to Java mappig Java to XML/WSDL mappig Core APIs SOAP support (icludig attachmets) Cliet ad Server Programmig models ivolvig geerated stub classes Cliet side ivocatio (stadard programmig model) Applicatio ivokes web service through geerated stub class JAX-WS rutime maps the ivocatio to SOAP, builds the SOAP message, processes the HTTP request Server side processig JAX-WS rutime processes HTTP, SOAP message, maps to RPC ad dispatches to target (class implemetig the web service) Prof.Dr.-Ig. Stefa Deßloch 30 Middleware for Heterogeeous ad Distributed Iformatio Systems

31 Mappig WSDL <-> Java Example WSDL 1.1 iterface defiitio:  <message ame= getlasttradeprice > <part ame= tickersymbol type= xsd:strig /> </message> <message ame= getlasttradepricerespose > <part ame= result type= xsd:float /> </message> <porttype ame= StockQuoteProvider > <operatio ame= getlasttradeprice parameterorder= tickersymbol > <iput message= ts:getlasttradeprice /> <output message= ts:getlasttradepricerespose /> </operatio> </porttype> Java service edpoit iterface: //Java public iterface StockQuoteProvider exteds java.rmi.remote { float getlasttradeprice( Strig tickersymbol) } throws java.rmi.remoteexceptio; Prof.Dr.-Ig. Stefa Deßloch 31 Middleware for Heterogeeous ad Distributed Iformatio Systems

32 Summary Service-orieted architectures SOAP defiitio, access, discovery of (web) services web services vs. REST services defies SOAP message structure ad messagig framework stateless, oe-way more complex patters "o top" (e.g., request/respose) provides covetio for doig RPCs usig SOAP support for extesibility, error-hadlig, flexible data represetatio idepedet of trasport protocols bidig framework for defiig protocol-specific bidigs SOAP/HTTP extesios beyod SOAP for addressig, reliable messagig (see ext chapter) Prof.Dr.-Ig. Stefa Deßloch 32 Middleware for Heterogeeous ad Distributed Iformatio Systems

33 Summary (cot.) WSDL UDDI supports descriptio of all iformatio eeded to access a web service iterface, operatio, message types bidig to specific protocol (e.g., SOAP) registry protocol extesios edpoit, service publish iformatio about busiess, services provided, ad the way to use them white, yellow, gree pages tmodels provide ifrastructure for busiess ad service "ame space" idetificatio, classificatio of busiess, services, protocols, ca "poit to" detailed service descriptios such as WSDL files APIs for maipulatig ad iquirig about registry cotet provided as web services Prof.Dr.-Ig. Stefa Deßloch 33 Middleware for Heterogeeous ad Distributed Iformatio Systems

34 Summary (cot.) Applicatio developmet Itegratio with programmig laguages, existig middleware Toolig support Programmig laguage bidig WSDL as the "IDL for web services" Mappig WSDL to PL (e.g., Java) eables geeratio of cliet proxies, server stubs for web services ivocatio Mappig PL to WSDL "publish" existig fuctioality as a web service Web services support based o covetioal middleware defie stadards for reusig/extedig existig programmig models ad middleware ifrastructure to support web service Java EE: use/publish servlets, stateless sessio beas to implemet WSs (JAX-WS) REST (Represetatioal State Trasfer) idea: model a set of services as resources with geeric iterface (get, put, post, delete) "lightweight", stateless web services Java EE: itegratio similar to web services, is based o JAX-RS API Prof.Dr.-Ig. Stefa Deßloch 34 Middleware for Heterogeeous ad Distributed Iformatio Systems

Architectural styles for software systems The client-server style

Architectural styles for software systems The cliet-server style Prof. Paolo Ciacarii Software Architecture CdL M Iformatica Uiversità di Bologa Ageda Cliet server style CS two tiers CS three tiers CS