Web Service - TUtorial 3 (Answer)

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Tutorial 3

1. Why is a service description necessary for representing Web services?

Answer:

• Web services need to be described as we are developing service-based application(assemble the services).

• After described, WS can be published, discovered, assembled in a manageable

hierarchy to deliver value-added service solution.

• Service description is typically used to making SOA loosely coupled.

• Service description is a machine-understandable specification describing the structure,

operational characteristics, and non-functional properties of a Web service.

• It also specifies the wire format and transport protocol.

2. What is the purpose of the Web Services Description Language (WSDL)?

Answer:

• WSDL is the service representation language used to describe the details of the

complete interfaces exposed by Web services and thus is the means to accessing a Web

service.

• Through the service description, service provider can communication all the specs for

invoking WS to the service requestor.

• WSDL is an XML-based specification schema for describing the public interface of a

Web service.

• This interface include:

– Operational information relating to a Web service

– XML message protocols supported by a Web service

– Data type information for messages, binding information (specific protocol to

be used) . – Address information for locating the Web service.

• WSDL allows the specification for transmission under SOAP.

• Both service provider and service requestor must agree WS description and

make use of that service. (a “contract” btw them)

• Essentially, WSDL is used to describe precisely

• what a service does, i.e. the operation the service provides,

• where it resides, i.e. details of the protocol address, e.g. URL.

• how to invoke it, i.e. details of the data formats and protocols necessary.

3. Define and describe the Web service interface (abstract interface).

Answer:

• The service interface definition describes the general Web service interface structure.

1. Data types - defining data types in the form of XML schemas or possibly other

mechanism.

2. Message - present message as either as an entire document or arguments to be

mapped to a method (WS) invocation.

3. Operation - the abstract definition of the operation for a message, such as

naming a method, message queue, or business process, that will accept and

process the message.

4. Port type - an abstract set of operations mapped to one or more

end points (port), defining the collection of operations for a

binding; the collection of operations, because it is abstract, can be mapped to multiple transports through various bindings.

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Tunku Abdul Rahman CollegeAdvanced Diploma in Science

AACS5274

Web Services



4. Define and describe the Web service implementation (concrete endpoint).

Answer:

• The service implementation binds the abstract interface to a concrete network address, to a

specific protocol, and to concrete data structure.

a) Binding - the concrete protocol and data formats for the operations and messages

defined for a particular port type.

b) Port - a combination of a binding and a network address, providing the target address of

the service communication.

c) Service - a collection of related end points (port) encompassing the service definitionsin the file; the services map the binding to the port and include any extensibility

definitions.

5. Can a single service contain multiple ports? What is the implication?

Answer:

Yes. It can contain multiple ports.

• A port identifies one or more transport binding for a given port type.

• Port types can be grouped for binding(s) which is how the services are connected over

network.

6. How does one-way operation differ from a request/response operation?

Answer:

One-way operation• An operation in which the service endpoint receives a message, but

does not send a response. E.g. a submission of an order to a purchasing

system, no immediate response.

• Thought of as asynchronous messaging and defines only input

message.

Request/response operation

• An operation in which the service endpoint receives a message and

returns a message in response. (similar with RPC-style).

• <operation> element is declared with a <input> (indicates a WS

receives a msg) and followed by a <output> (indicates a WS responds to the

msg) element, it defines a request/response operation.

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7. How does a notification operation differ from a solicit/response operation?

Answer:

Notification operation

• An operation in which the service endpoint sends a message to a client,

but it does not expect to receive a response.

• This type of messaging is used by services that need to notify clients of

event e.g subscriber

• It contains an <output> element but no <input> message.

Solicit/response operation

• An operation in which the service endpoints sends message and

expects to receive an answering message in response. (opposite of

request/response operation)

• In this messaging pattern, the <portType> first declares <output> and

then an <input> element. E.g service sends a order status to a client and

receives back a receipt.

8. With the aid of a diagram, explain how the WSDL architecture works.

Answer:

Role of a WSDL file in a Web services interaction:

• When a Web service is published, a Web service administrator posts a

link to the Web service’s WSDL document in an XML registry /WSDL

repository.

• The WSDL file is available when an application, such as SOAP client,

searches a registry to locate a Web service. A client accesses the

WSDL document in WSDL Repository to acquire information aboutthe Web service and to create a SOAP message with the appropriate

structure to communicate with the service.

• Then, using the information in the WSDL document, the client invokes

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XML Registry or WSDL

Repository

Web

ServicesClient

2. Retrieve

WSDL

document

1. Web Services

administrator

posts WSDL

document to

WSDL

repository

3. Invoke



the Web service.

9. What TWO (2) purposes does the <binding> element serve?

Answer:

- The binding element links the abstract elements with the concrete elements of the WSDL.

- It provides a container for information like protocol and address of the service.

10. Based on the Web Services Description Language (WSDL) document given below, identify and explain

each of the WSDL elements in detail.

1 <?xml version="1.0" encoding="utf-8" ?>

2 <wsdl:definitions xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"

3 xmlns:tns="http://tempuri.org/"

4 xmlns:http="http://schemas.xmlsoap.org/wsdl/http/"

5 targetNamespace="http://tempuri.org/"

6 <wsdl:types>

7 <s:element name="calculateSalary">

8 <s:complexType>

9 <s:sequence>

10 <s:element minOccurs="1" maxOccurs="1" name="basic" type="s:int" />11 <s:element minOccurs="1" maxOccurs="1" name="OT" type="s:int" />

12 </s:sequence>

13 </s:complexType>

14 </s:element>

15 <s:element name="calculateSalaryResponse">

16 <s:complexType>

17 <s:sequence>

18 <s:element minOccurs="1" maxOccurs="1" name="Result" type="s:int" />

19 </s:sequence>

20 </s:complexType>

21 </s:element>

22 </s:schema>

23 </wsdl:types>

24 <wsdl:message name="calculateSalarySoapIn">

25 <wsdl:part name="parameters" element="tns:calculateSalary" />

26 </wsdl:message>

27 <wsdl:message name="calculateSalarySoapOut">

28 <wsdl:part name="parameters" element="tns:calculateSalaryResponse" />

29 </wsdl:message>

30 <wsdl:portType name="ServiceSoap">

31 <wsdl:operation name="calculateSalary">

32 <wsdl:input message="tns:calculateSalarySoapIn" />

33 <wsdl:output message="tns:calculateSalarySoapOut" />

34 </wsdl:operation>

35 </wsdl:portType>

36 <wsdl:binding name="ServiceSoap" type="tns:ServiceSoap">

37 <soap:binding transport="http://schemas.xmlsoap.org/soap/http" />

38 <wsdl:operation name="calculateSalary">

39 <soap:operation soapAction="http://tempuri.org/calculateSalary"40 style="document" />

41 <wsdl:input>

42 <soap:body use="literal" />

43 </wsdl:input>

44 <wsdl:output>

45 <soap:body use="literal" />

46 </wsdl:output>

47 </wsdl:operation>

48 </wsdl:binding>

49 <wsdl:service name="Service">

50 <wsdl:port name="ServiceSoap" binding="tns:ServiceSoap">

51 <soap:address location="http://localhost:WebSite/Service.asmx" />

52 </wsdl:port>

53 <wsdl:port name="ServiceSoap12" binding="tns:ServiceSoap12">

54 <soap12:address location="http://localhost:WebSite2/Service.asmx" />

55 </wsdl:port>

56 </wsdl:service>

57 </wsdl:definitions>

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Web Service - TUtorial 3 (Answer)