Just-in-time Integration

Transcription

1 Just-in-time Integration An application retrieves only at run-time, which web service will be used finally. The service is integrated just in time. Comparable with late binding in object-oriented programming Process is based on Web Service Architecture 1. Registration Service Provider Service Registry 3. Binding 2. Search Service Consumer

2 Technology Layers for Web Services Discovery Description Packaging Transport Network Modularization of tasks Adapted to the Internet Stack Discovery: find the right description of a Web Service Description: describe a Web Service Packaging: encode the data in a generally understandable format (=marshalling, serialization) Transport: Data transport between processes Network: Communication between machines in the net

3 N-Tier Architectures Distributed web applications are often realized a so-called N-tier (N=2,3,4) Each Tier (Layer, Level) has its own task Advantages Low complexity of the components Distribution of implementation tasks Flexibility in distributing the various tasks (thin client) Easy maintenance (no client software, version update) Scalability, Security

4 3- und 4-Tier-Architectures Tier 1: Presentation Tier 2: Business Logic Tier 3: Data Business Logic Tier 1: Presentation Tier 2: Web Server Tier 3: Application Server Tier 4: Data

5 Presentation Layer User Interface Often implemented in a web browser as a thin client without any application logic Important function Pull user input Display output of the application on the server side Important technologies HTML and WML, mostly forms Java Applets

6 Business Logic Layer In this layer most of the application logic is realized, for example in e-commerce - shopping basket functions - and payment functions this layer can be split physically for increased security and scalability The web server, that forms the direct interface to the user The application server, which provides further services (transactions, security) Technologies: Servlets, JSP (Java Server Pages), ASP (MS Active Server Pages), CORBA, EJB (Enterprise Java Beans)

7 The Data Layer The layer is responsible for the core data of the application, e.g. in e-commerce - customer data - product data - orders Typical implementations Database systems like DB2, Oracle, SQL Server Enterprise Resource Planning System like R/3

8 Reasons for Service Descriptions The caller must know how a service functions in order to call it in a proper way - standard solution: text description on a webpage - - better solution: use a formal and machine interpretable description based on a service description language normally the interfaces are being described; thus: Interface Definition Language (IDL)

9 The Role of Formal Descriptions in the Web Service Architecture This scheme functions only with formal descriptions All three steps require service descriptions: Registration advertises the functions of the service Search is based on formally defined properties Binding of the service used the formal description for ensuring proper calls and execution 1. Registration Service Provider Service Registry 3. Binding 2. Search Service Consumer

10 Goals of a Formal Description of Web Services A formal description should answer the following questions: Who is using this service? Who is offering is? What is offered? Service Interface Where is the service offered? Servers, URLs Why is the service offered? Task, in most cases only informal description How is the service offered Description of the service interface

11 WSDL = Web Service Description Language WSDL is a proposed standard of W3C. Proposed by IBM, Microsoft and others download: WSDL like SOAP is an application of the XML specification. A WSDL document is compliant with a WSDL schema definition. A WSDL specification answers three questions: What is the service doing which operations are offered? How is the service accessed data formats, messages? Where is the service?

12 WSDL Information Model A WSDL specification consists of Abstract specification of message types Concrete Implementations of this specifications, i.e. the actually available service the description of the abstract functions is based on the porttype, the description of the current implementation is based on the binding element. The binding is combined with an address, thus a concrete terminal point is known, which allows one to activitate the implementation.

13 WSDL: Elements of the Language porttype: the abstract definition of an interface (like a Java Interface) message: s set of parameters, that are used by the operations Typen: all data types, that are used in operations binding: describes, how elements of an abstract interface are mapped onto a concrete representation (coding schema, SOAP over HTTP) port: describes, how a binding is realized at a concrete terminal service: a set of terminals

14 Relations between WSDL Elements part type (abstract)) message (abstract) operation Abstract Interface PortType (concrete) message (concrete) message Concrete Binding concretion by includes service concrete terminal (port)

15 Structure of a WSDL Document A service is a collection of ports. A port has an abstract definition (porttype) and a concrete realization (binding). PortTypes a collections of abstract operations. Data Types <wsdl:types/> Messages <wsdl:message/> Interfaces <wsdl:porttype/> Services <wsdl:/binding/> <wsdl:service>

16 XML Schemata for Data Description It should be clear for a service description, how the exchanged data types are structures In principle WSDL allows the use of any data description language, but there is a clear preference for XML schemata Namespaces are being used, so that any schema description can be applied inside the definitions. Names of data types are used in a local context by the introduction of namespaces.

17 Abstract Service Description <definitions=...> <wsdl:message name= sayhello_in > <part name= name type= xsd:string /> </wsdl:message> <wsdl:message name= sayhello_out > <part name= greeting type= xsd:string /> </wsdl:message> <wsdl:porttype name= HelloWorldInterface > <wsdl:operation name= sayhello > <wsdl:input message= tns:sayhello_in /> <wsdl:output message= tns:sayhello_out /> </wsdl:operation> </wsdl:porttype> </definitions>

18 A SOAP-over-HTTP Binding <wsdl:binding name= HelloWorldBinding type= tns:helloworldinterface > <soap:binding stype= rpc transport= /> <wsdl:operation name= sayhello > <soap:operation soapaction= urn:hello /> <wsdl:input> <soap body use= encoded... /> </wsdl:input>... </wsdl:operation> <wsdl:binding>

19 Example: QA for stock market A service is described, which receives a ticker symbol as a query and replies with the current value of the stocks referred to. We describe the service in three files: The schema definition stockquote.xsd The operations in stockquote.wsdl The service in stockquoteservice.wsdl

20 stockquote.xsd <?xml version= 1.0?> <schema targetnamespace=" xmlns=" <element name="tradepricerequest"> <complextype> <all> <element name= tickersymbol" type="string"/> </all> </complextype> </element> <element name="tradepriceresult"> <complextype> <all> <element name="price" type="float"/> </all> </complextype> </element> </schema>

21 stockquote.wsdl <?xml version="1.0"?> <definitions name="stockquote" targetnamespace=" xmlns:tns=" xmlns:xsd1=" xmlns:soap=" xmlns=" <import namespace= location= > <message name="getlasttradepriceinput"> <part name="body" element="xsd1:tradepricerequest"/> </message> <message name="getlasttradepriceoutput"> <part name="body" element="xsd1:tradepriceresult"/> </message> <porttype name="stockquoteporttype"> <operation name="getlasttradeprice"> <input message="tns:getlasttradepriceinput"/> <output message="tns:getlasttradepriceoutput"/> </operation> </porttype> </definitions>

22 stockquoteservice.wsdl <?xml version="1.0"?> <definitions name="stockquote" targetnamespace=" xmlns:tns=" xmlns:soap=" xmlns=" <import namespace= location= > <binding name="stockquotesoapbinding" type="tns:stockquoteporttype"> <soap:binding style="document" transport=" <operation name="getlasttradeprice"> <soap:operation soapaction=" </operation> </binding> <service name="stockquoteservice"> <documentation>my first service</documentation> <port name="stockquoteport" binding="tns:stockquotesoapbinding"> <soap:address location=" </port> </service> </definitions>