PWS Exam Questions 2005 - 2010 V1.0

ID2208 Programming Web ServiceExam questions & answers

Lecture 1: SOA and introduction:

1. What is Service Oriented Architecture (SOA)? Which roles and which operations it assumes?

SOA is an architectural concept where the software components are modeled as services.These services will have a well-defined interface through which the other services can interact with each other to achieve a business purpose. It enables the publishing and consumption of software services.

The various roles played are as followsServices Provider: These denotes the entity that develops and deploys the web services at run-time, create the service description, publishes or registers the service description to several service registries and handles the incoming service invocations from service requesters. It can be viewed as the server side of the client-server relationship, the handles the incoming requests from the service requester.Service Requester: This denotes the entity that consumes the web service. Its responsibility is to find the service description from one or more services registries, to invoke and bind to the appropriate service provider. It can be viewed as the “client” side of the client-server relationship.Service Registry: It acts as a match maker between the service provider and the service requester. It allows the service provider to publish his service description in its registry and allows the service requester to search and use the service description.

The various operations in SOA:Publish: It is an act of service registration and service advertisement that takes place between the service provider and the service registry. This operation is done by the service provider, in which it publishes the description of its web services on the service registry thereby making it available for the service requesters. In simple terms, it is an act of moving the web service description to the service registry's structure.Find: It is an act of service discovery that takes place between the service requester and service registry. This operation is done by the service requester. The service requester provides certain search parameters like type of service, quality of service etc and the service registry returns those services descriptions that matches the search criteria.Bind: It is an act in which the service requester binds with the service provider using the information from the provider's service description it obtained from the service registry. It can either be sophisticated and dynamic or static. In this operation, both the provider and requester communicate with each other directly without the involvement of the service registry.

2. Show layers and associated Web Services technologies of a Web Service interoperability stack

Programming Web Services! Exam questions & Answers

V1.0 Last modification: 01/06/2010!

3. Is there any difference between SOA and Web services? JustifyThe Web services is some kind of SOA. One of the differences is that the Web services are based on message passing and XML, but SOA could use message passing or Remote Method Invocation (RMI) or Remote Procedure Call (RPC).

4. Give advantages of Web services as a technology for software integrationa. Operate using open, text-based standardsb. Promote a modular approach to programmingc. Significantly reduce the cost of enterprise applications integrations and B2B

communicationsd. Can be implemented incrementallye. The usage of HTTP enables the web service messages to tunnel through firewalls of

different enterprises.f. The usage of XML text-based formats for representation of messages eliminates the

byte-order concerns.g. The expressive nature of attributes and nested elements in XML made it easier to

represent complex data structures. h. The implementation of SOA style enabled the applications to locate and bind with

the service providers dynamically thereby providing maximum flexibility.

5. Firewalls present a special challenge to integrating inter-enterprise systems. How is this problems solved for web services?

Firewalls allow the HTTP messages to pass through them. So, we write our own XML text- based protocol message and place it on HTTP and send it across the firewall. This approachof wrapping our SOAP message with the HTTP so that it can safely pass through the firewall is called as HTTP Tunneling.6. Explain what is “Software as a service”? What is its main difference with

traditional software? (2010)Software as Service (Saas) isa software application delivery modelwhere

• a software vendor develops a software application• hosts the software application and



• operates the applicationfor use by its customers

The main difference between Saas and traditional software is that customers do not pay for owning the software, but rather for using it.

7. Explain the difference between human-centric, application-centric and automated web

Invocation: In human-centric approach the humans should invoke the service explicitly. In application- centric, the middle ware layer invokes the service. In the automated web, both the discovery ! and invocation of service are done by the middle ware layer.

Location: In human-centric approach, the humans should have a knowledge of the exact location of the service. In both application-centric and automated web, humans do not need to have the location of the service.

coupling: The human-centric approach is faster and tightly coupled, whereas both application-centric and automated web are loosely coupled and relatively slower.

8. What are the advantages of web services technology over the traditional distributed computing technologies like CORBA, RMI and COM ?

Invocation: CORBA / RMI / COM are synchronous method invocation techniques, where as Web services are asynchronous.

Communication: Web services uses a simple text-based XML messaging to communicate, whereas! CORBA / RMI / COM does not use XML messaging.

Coupling: CORBA / RMI / COM makes the application integration tightly coupled, whereas Web services makes application integration loosely coupled thereby allowing it to be highly flexible. - CORBA / RMI / COM support only RPC whereas web services support both RPC and document-centric messaging.

Integration: CORBA / RMI / COM are suitable for intra-enterprise application integration, whereas Web service is suitable for inter-enterprise application integration.

9. Show the web services protocol stack.



10.Explain the interaction between service requester, SOAP, WSDL and UDDI in realizing a web service application.

10.1 The service requester queries the UDDI registry to find a service ! matching the search parameters.10.2 The UDDI returns the location of the WSDL for the appropriate service.10.3 The requester accesses the WSDL and gets the necessary data to invoke ! and use the Web service.10.4 The requester creates a SOAP-message request and sends it to the web ! service.10.5 The web service processes the incoming SOAP-message ! request and ! sends back the SOAP-message response to the service !requester.

11.What are the various service discovery approaches? Explain their advantages and disadvantages. Which of these approaches are being used in SOA ? Service discovery approaches are:

• Registry approach.• Registry first and the you can get some information.• It has centralized register

• Indexed approach. (Google)• They registry the index of services, like google. • It doesn't has centralized register.

• Peer-To-Peer approach.• Services stores in some nodes. Then it know some neighbors. When it has to find

some services, it ask to the neighbors. If they know, then finish; it not, the neighbors will ask to their neighbors.

• Some times it can't guarantee that it can find the right services.

Registry approach is centralized and therefore faster than the other approaches. It has the limitation that only the services registered in the registry are available.

Indexed approach involves the searching through out the web and therefore it is slower. But the requester is left with a wider window of accessing many other web services.



In Peer-To-Peer approach, the search is to be done on only those peers attached to the registry. Thus it is relatively faster than indexed approach and relatively slower than the registry approach. The requester can only access the services registered in the peers.

SOA uses the registry approach.

12.List the properties of SOA?1. Logical view of sources2. Message exchange between requester and provider3. Meta data description oriented4. Small number of operations, large and complex messages5. Network orientation6. Platform neutral

13.What are the differences between Web services and Application Service Providers?

Centralization: Web services is a decentralized approach. ASP is a centralized approach.

Permission: The service requester needs the permission of ASP to use a service. Whereas the service requester does not need the permission to use a service in a web service.

Granularity: Web Services can have different granularity, but ASP cannot.

14.Compare the component based model and web service model.

Coupling: CB models are tightly coupled. WS models are loosely coupled.Integration: CB models are for intra-enterprise applications. WS models are for inter-enterprise applications.Protocols and technologies: CB uses different protocols and technologies. The Web services model uses common protocols and technologies.



Lecture 2: XML1. Explain why do we have different XML parsing models?

It is because that XML parsing needs to do trade-off between memory efficiency, computational efficiency and ease of programming.

2. What are the input(s) and output(s) of an XML Schema compiler? How many times we need to invoke schema compiler during parsing?

Input(s): XML schema.Output(s): un-marshaling and marshaling modules specific to the schema.

We need to invoke the XML schema compiler only once.

3. What are the main parsing models? Give their advantages and disadvantages.

Parsing models are: Push, Pull, One-Step and Hybrid.Push: (SAX)

• Advantages:• Least usage of memory.• Simple to handle.

• Disadvantage:• It is a single-pass parsing technique hence no random access of nodes. • It is read-only (in case of SAX).

Pull:• Advantage:• Disadvantage:

One-step:• Advantage:

• Easy to manipulate XML documents.• Parsing done in a single step.

• Disadvantage:• More memory usage.

Hybrid:• Advantage: Efficient usage of time and memory.• Disadvantage:

Model Memory efficiency Computation efficiency

Ease of program.

Pull

Push (SAX)

One-Step (DOM)

Hybrid

High Highest Low

High High Low

Low Low High

Medium Medium High



4. We considered 4 parsing models for XML. Briefly explain them and suggest in which cases each of them is more suitable to use. (2010)

The parsing models are Push, Pull, One-Step and Hybrid.

Pull parsing:• The application always has to ask the parser to give it the next piece of information

about the document.• The XML community has not yet defined standard APIs for pull parsing.

Push parsing (SAX)• The parser sends notifications to the application about the types of XML

document pieces.• The push parsing is also commonly known as event-based parsing.• Standard: Simple API for XML (SAX)

One-step parsing (DOM)• The parser reads the whole XML document and generates a data structure and

describing its contents.• The data structure is typically deeply nested• The W3C has defined a Document Object Model (DOM)

Hybrid parsing• This approach combines characteristics of the other three parsing models• For example, combining pull parsing with one-step parsing. • The application thinks itʼs working with a one-step parser, but as the application

keeps accessing more objects on the DOM tree, the parsing continues incrementally.

5. What is the difference between import and include in XML schema reuse? How?Namespace collision: Using include you can retrieving the definitions but it makes no namespace changes. Using import it merges schemas from multiple namespaces into one schema. With import is possible to merge the contents of the namespace into other namespace. You just have to specify the new namespace when you are importing.

Different documents: With include, the fully qualified name of the elements needs to be used. Then, if we include different document you cannot hide this fact. Whereas on using import, this fact can be hidden cause we do not need to use the fully qualified name. 6. What is well-formedness and what is validity of an XML document? Who checks

them and what kind of information is required for their checking?

An XML document is said to be well-formed if it is conformant with the XML syntax rules.

An XML document is said to be valid if it is conformant with the applied format as defined either in a Document Type Definition (DTD) document or a XML schema document.

The XML parser checks for both well-formed ness and validity of the XML document.

To check the well-formedness the parser needs the XML document alone.



To check the validity of the document the parser needs the XML document and either its DTD or schema document.

7. Why might we need name spacing of attributes in an XML document? Give an example.

We need name spacing of attributes for the following reasons.• To avoid the recognition problem where the parser can understand the semantic

meaning of attributes.• To avoid the collision problem where two identical attributes are used for

mentioning of distinct entities in the same document.• To extend the information provided by an XML element without having to make

changes directly to its document type.

Consider a scenario where we have 2 elements “<order>” and “<item>”. If we need to have an attribute named “priority” for both the elements. In order to clearly understand their peculiar usage we need to use unique namespace for the attribute in each element.

8. Show how you represent phone number “+46 8 790 04 13” in XML using elements and using attributes? Give advantages and disadvantages of one representation compare to another?

Using Elements: <ContactNo> <CountryCode>46</CountryCode> AreaCode>87</AreaCode> <PhoneNo>900413</PhoneNo></ContactNo>Using Attributes: <ContactNo CountryCode=”46” AreaCode=”87” PhoneNo=”900413”> </ContactNo>

Some disadvantage of Attribute regard to elements are:1. Not multiple values: It cannot contain multiple values2. Not easily expansion: Itʼs not easily expandable3. Not usable to describe structures4. Harder to be manipulated by program code.

9. Compare advantages and disadvantages of DOM and SAX approaches to XML parsing.

• DOM is in memory structure, SAX is not• SAX is simpler than DOM in many ways• SAX is event-based API• DOM parser in space while SAX parses in time

10. Explain difference between document centric and data-centric XML. Which one is used in Web Services? Compare them.

• Ratio markup: The ratio of markup to content in data-centric is much higher than in document-centric XML

• Machine-generated: Data-centric often includes a machine-generated information• Structure: The document and tags are highly structured in data-centric.• Data structure: Data-centric is easily related to a data structure• Living Time: Data-centric usually living shorter time than document-centric

Data-centric XML is used in web services



11. Explain the idea of XML schema compiler.

The XML schema compiler is a tool that analyzes the XML schema and code-generates the corresponding marshalling and un-marshalling modules.

It needs to be invoked only once.Later the application can use the code-generated modules without requiring the schema compiler.

12. What are the 2 XML processing techniques? Explain the differences between them. Give examples for both.

The 2 processing techniques are• Syntax oriented processing – SAX and DOM• Data oriented processing - JAXB

XML Structure: Syntax oriented processing depends on the XML structure. Applications have to work with elements, attributes and pieces of text. Whereas data centric approach does not depend on the XML structure.XML Schema compiler: Syntax oriented approach does not use any XML schema compiler where data-centric uses XML schema compiler.

13. What is the difference between a pre-defined data type and constructed data type.

Pre-defined data type are the data types that are already defined in the XML. eg: string, positiveInteger, date, time etc.

Constructed data type can be any new data types which are constructed from the pre-defined data types.

14. What is the difference between simpleType and complexType elements in XML schema.

A simple element is an XML element that can contain only text. It cannot contain any other elements or attributes.

A complex element is an XML element that contains other elements and/or attributes.



15. Discuss about restrictions and extensions in XML schema.

Restriction implies that the values that an XML element contains are bound to certain rules as defined in the schema document. For e.g. : The usage of “xsd:enumeration” restricts the XML elementʼs values to limited set of values. Similarly the usage if “xsd:pattern” restricts the XML elementʼs values to a certain pattern.

Extensions imply that the existing functionality of an element can be extended to an additional set of functionality as defined in the XML schema.

16. List the basic schema reusability mechanisms in XML schema? Explain the difference between intra-document reusability and inter-document reusability.

Reusability mechanisms:• Element reference• Attribute reference• Model groups reference• Schema includes• Schema imports

In intra-document reusability the elements are reused in the same schema document.In inter-document reusability the elements of a schema document are reused in adifferent document.

17. Which mechanisms for re-use in XML do you know? Briefly explain each of them. (2010)

We can classify the mechanism to reuse XML into two types: Intra-XML reuse and Inter-XML reuse.

The Intra-XML reusage refers to the mechanism that reuse a part of the same document. In this case, the keyword "ref" is used.

The inter-XML reusage refers to the mechanism that reuse a part of other document as their own. There are two types: "include" and "import".

When we use "include" we are reusing a part of other XML document without changing its original namespace. But if we want to reuse parts of different documents that have the same namespace, then the namespace collision could be avoid using "import". With "import" we can merge the components of the namespace and assign them new namespace

18. What is the role of “targetNamespace” attribute in XMl Schema description?The targetNameSpace attribute of a schema elements identifies the namespace of the documents that will conform to the schema.

It indicate where the element defined by this schema come from.

19. Explain why do we have different XML parsing models?



The reasons there are so many different models for parsing XML have to do with trade- offs between memory efficiency, computational efficiency, and ease of programming.



Lecture 3.1: SOAP

1. Give advantages of using SMTP for transporting SOAP messages.

• Transfer context information: It has extensible headers that can be used to transmit context information.

• Authentication: Both sending and receiving of e-mail messages can be configured to require authentication.

• Multicast: E-mail can support one-to-one and one-to-many participant configurations.

• Buffering and queueing: E-mail messaging is buffered and queued with reliable dispatch.

• Scalability: The Internet e-mail server infrastructure is highly scalable.

2. What are intermediaries in SOAP and what is their purpose?

Intermediaries are the nodes that exist in the SOAP message path in between the service requestor and the service provider. Their purpose is to process the header part of the SOAP message thereby providing secured exchange of SOAP messages, notarization, providing message tracing facilities etc. It therefore provides horizontal extensibility

3. What are possible values of the role attribute in SOAP headers? Briefly explain the meaning of its special values.

The possible values of the role attribute will be the URI of the intermediary node or that of the ultimate service provider node.

The special values are• next: It denotes that the header element should be processed by the next

intermediary node.• none: It denotes that none of the nodes should process the header element. The

“mustUnderstand” attribute becomes ineffective for this role.• ultimateReceiver: It denotes that the node at the receiving end of the SOAP

message path will process the body part. Omitting the role attribute or setting it to “” also denotes that the message should be processed by the final node

4. What is vertical and horizontal extensibility in SOAP?

Using the headers to add functionality for the SOAP messages is called as the vertical extensibility. This can include adding information regarding the security, routing, notarization etc. It is implemented over the middleware layer of the SOAP binding framework.

Horizontal extensibility is the process of targeting the different parts of the same SOAP message to different recipients. This is achieved through the intermediaries. This is done in order to allow the processing of the header elements by different nodes.

5. Why do we place some information in the headers and some information in the body of SOAP message? What is/are main criteria(s) for making decision about such placement?



Header contains auxiliary information and itʼs optional. Body contains main information. Header can contain authentication information, routing information, actor/role attribute, mustUnderstand attribute, ...

The Body contains the actual SOAP message intended for the ultimate endpoint of the message. The header contains informations that could be processed by intermediate nodes.

6. Which predefined attributes of SOAP headers you know? Briefly explain them?

Predefined attributes of headers are:• Actor/role: It denotes the node in the SOAP message path that will process the

SOAP message. The role attribute can also have some special values as follows.• next: It denotes that the header element should be processed by the next

intermediary node.• none: It denotes that none of the nodes should process the header element. The

“mustUnderstand” attribute becomes in-effective for this role.• ultimateReceiver: It denotes that the node at the receiving end of the SOAP

message path will process the body part. Omitting the role attribute or setting it to “” also denotes that the message should be processed by the final node

• mustUnderstand: It indicates that the receiver processing the Header must or not recognize the element. If the receiver does not recognize the element it will fail when processing the Header.

7. What are RPC conventions in SOAP? How different types of parameters are sent in SOAP messages?

The name of the request struct is the name of the method and arguments are puts inside as elements.

The RPC convention said that the name of the response struct is the name of the method with Response appended to the end.

There are two types of parameters that could be send in SOAP message: out and inout.

8. Explain the SOAP processing model?

1. Determine the set of roles that the node is to act. This is decided by going through all the header elements.

2. Identify all the header blocks targeted at the node that are mandatory.3. If any of the elements identified in the above step are not understood then generate a

SOAP fault message with code set to env:mustUnderstood. And processing in stopped.4. Process all mandatory headers targeted at the node. If the node is the ultimate node

then the body is also processed.5. Relay the message if it is intermediary.

9. What is a feature in SOAP? How can it be expressed?

Feature is a semantic that has a name and a specification. Eg: security, reliable messaging, quality of service etc. They are expressed by bindings and modules.

10. What is role in SOAP headers and what kind of information they usually include?



Role specifies the node which has to process the header element. It is usually denoted as a URI of the node. It can have some special values like none, ultimateReceiver and next.

11. What HTTP operation is usually used in SOAP exchanges?

The HTTP POST operation is usually used by the SOAP message exchanges.

12. Explain what is Message Exchange Pattern (MEP)? What are standard MEPs in SOAP?

MEPs are features that specify how many messages move around in a given interaction, from where they originate and to where they terminate. The 2 standard MEPs are

Request-Response MEP:

This involves a requesting node and a responding node. The requesting node sends its requests in the form of a SOAP message. The responding node processes this SOAP request and sends back the SOAP response message.

SOAP Response MEP:

This involves a requesting node and a response node. The requesting node does not necessarily send a SOAP message, so the responding node does not trigger the SOAP processing model. But the response message will be a SOAP response message.

13. What is the main difference in processing SOAP message by intermediary node and by service provider node? (03 - 2010)



The intermediary node processes header and the service provider processes both header and the body.

14. In the class we considered the following guiding schema for selection of data encoding in SOAP. Your task is to fill in cells which have question mark (you can put labels into the cells and then refer to them)

15. What is SOAP

data model?

Give an example.The data model is an abstract representation of the data structures.



<product! soapenv:encodingStyle=”http://www.w3.org/2003/05/soap-encoding”>! <sku> 947-TI </sku>! <name>Titanium glider </name>! <type> skateboard </type>! <desc> Street-style titanium </desc>! <price> 129.00 </price>! <inStock> 36 </inStock></product>

The encoding is a set of rules to map that data model into XML to send by SOAP message.

16. Explain meaning of feature and properties in SOAP? Give an example.

The feature is a semantic that has a name and a specification. For example, the authentication feature or the colour feature.

The properties are pieces of states named with URI which affect the operation of features. For example, for the security, the properties could be the username and the password.

17. Explain how the same feature can be expressed by binding and by modules.

A binding is a means for performing functions below the SOAP processing model; and a module is a means for performing functions using the SOAP processing model, via headers.

For example, if we want to have a “security channel” feature, we might imagine a SOAP binding to the HTTPS protocol, which would specify that it implements the http://skatestown.com/secureChannel features. The binding specification would indicate that it natively supports this feature.

Using SOAP module it could provides encryption and signing of a SOAP message across any binding.

Lecture 3.2: RESTful



1. What are advantages and what are disadvantages of RESTful services in comparison with Web services?

Advantages of RESTful• Lightweight: it doesn't require a lot of markup• Easy to build: It doesn't required any toolkit. • Low bandwidth consuming

Disadvantage of RESTful• Service discovery: Client should know the address of the service.• Not complex requirements: It cannot address complex requirements• Not asynchronous mode: It cannot handle asynchronous processing and invocation• Mutual understanding: The service producer and the service consumer have to had a

mutual understanding of the context and the content.



Lecture 4: WSDL

1.Draw a WSDL informational model

2. What is a purpose of having “parts” in the WSDL “messages”? Give an example when this is used.

The part mechanism in WSDL is to decompose the WSDL messages in to simpler units or parts. Each part can be shown in different ways depending on the network protocol chosen for the web service.The part may be referred by the binding in order to specify the binding-specific information about the part.

Example of usage:! <message name=”checkInvoiceRequest”>! ! <part name=”invoiceNumber” type=”xsd:integer”/>



! </message>The part in the above WSDL code refers to the invoice number parameter to be sent to the web service.

3. Explain difference between functional and non-functional Web service description. Which WS-specifications can be used for each of them?

The functional description defines details of how theWeb service is invoked, where itʼs invoked, and so on.This description is focused on details of the syntax of the message and how to configure the network protocols to deliver the message.

The nonfunctional description provides other details that are secondary to the message. For example, security policy or privacy policy.Other example could be that It could instruct the requestorʼs runtime environment to include additional SOAP headers

WSDL can be used for functional description.WS-Policy can be used for non-functional description. WS-Policy acts as a container for security policies and other policies.

4. Which components of a WS description present answers to each of the following questions about the services: what, who, why, where, how?

What: WSDLWho: WS-PolicyWhy: WS-PolicyWhere: WSDLHow: WSDL and WS-Policy.

5. Explain the differences between the “document” and “RPC” values of the style attribute of the binding element. For which kind of “portType” you should use a “document” style binding?

The style attribute of binding indicates that operations will follow a document-centric approach or a RPC approach. The document-centric approach means the body of the SOAP message is to be interpreted as XML.



The RPC approach indicates that binding uses the Remote Procedure Call (RPC) conventions for the SOAP body.

The document style should be only used when itʼs binding for portTypes that reference messages that contain parts using the element attribute.If a portType references a message whose parts use the type attribute, you should define only RPC bindings for it.

6. What does the binding element serve for WSDL description?

The binding element provides the concrete implementation of the WS interface defined by the portType element. It denotes the protocol that will be used to bind and send the SOAP messages, the style (RPC or document-centric) of the message, operations and their corresponding messages to be sent and received.

7. Normal form in WS-Policy. What does it mean? Give an example of its usage.

It means that the policy assertions are re-written so that all the possible combinations are considered. It usually begins with the wsp:ExactlyOne.

Example:

! <wsp:Policy ...>! ! <wsp:All>! ! ! <wsp:ExactlyOne>! ! ! ! <nsSecurityAssertion wsp:Optional=”true” />! ! ! ! <nsReliableMessagingAssertion />! ! ! </wsp:ExactlyOne>! ! ! <nsTransactionAssertion />! ! ! <nsAuditAssertion />! ! </wsp:All>! </wsp:Policy>

After the normalization, it will be like!! <wsp:Policy ...>! ! <wsp:ExactlyOne>! ! ! <wsp:All>! ! ! ! <nsSecurityAssertion/>! ! ! ! <nsTransactionAssertion />! ! ! ! <nsAuditAssertion />! ! ! </wsp:All>! ! ! <wsp:All>! ! ! ! <nsReliableMessagingAssertion />! ! ! ! <nsTransactionAssertion />! ! ! ! <nsAuditAssertion />! ! ! </wsp:All>! ! ! <wsp:All>! ! ! ! <nsTransactionAssertion />! ! ! ! <nsAuditAssertion />! ! ! </wsp:All>! ! </wsp:ExactlyOne>



! </wsp:Policy>

8. Explain policy normalization, merging and intersection. Why and when do we need them?

Normalization: In normalization, the policy assertions are re-written so that all the possible combinations are considered. It usually begins with wsp:ExactlyOne.

Merging: Union operation in set theory. It put together all the possible policies.

Intersection: It involves the merging of two policies into a single one where only those policies that are common to both are considered.

We normalize the policy cause for merging and intersection itʼs easier do them if the policy is already in normal form.

Merge is used when we have hierarchy of elements and each element has its own policy. Then put all together we can create the join policy for all them.

The intersection is applied when the sender and the receiver have different policy, and the policy can be applied only when both of them understand it. If one of them cannot understand it, you cannot send the message. Then we can make intersection of the policies and apply it both to the receiver and the sender.

9. What are major elements of WSDL specification?



10.What is role of targetNamespace attribute in WSDL definition?Generally, the attribute targetNamespace defines how to form QName, portType, and so on. And how to combine WSDL descriptions that span multiple files.In Java and WSDL mapping, when the stub class is generated from binding, the name of class, package is taken from targetNamespace.

11. Explain role of the binding element in a WSDL document. Which standard binding extensions are defined in WSDL

Binding element defines how will the message be transmitted and what are SOAP-specific details (message format and protocol details).

The standard binding extensions that are defined in WSDL are SOAP, HTTP GET/POST operations, and MIME attachments.

12. What are WS-Policy operators? Briefly explain them.

The WS-Policy operators are:

1. All: This policy states that all of the assertions are in effect.! Example:

! ! <wsp:Policy name=”PolicyExample1” ! ! ! TargetNamespace=”http://ww.skatestown.com/policies” >! ! ! <wsp:all>! ! ! ! <Assertion:A />! ! ! ! <Assertion:B />! ! ! ! <Assertion:C />! ! ! </wsp:all>! ! </wsp:Policy>

2. ExactlyOne: This policy states that ONLY ONE of the assertions A, B and C is effect.

! Example:



http://ww.skatestown.com/policies

http://ww.skatestown.com/policies

! ! <wsp:Policy name=”PolicyExample2”! ! ! TargetNamespace=”http://www.skatestown.com/policies” >! ! ! <wsp:ExactlyOne>! ! ! ! <Assertion: A />! ! ! ! <Assertion:B />! ! ! ! <Assertion:C />! ! ! </wsp:ExactlyOne>! ! </wsp:Policy>

3. OneOrMore: This policy states that some subset of the policy assertions listed as child element is in effect.

4. Others: The operators can nest. Any of the Assertion elements can be replaced by an operator.



http://www.skatestown.com/policies

http://www.skatestown.com/policies

Lecture 5: UDDI

1. What are the main registry requirements?

Basic:• A set of data structure specifications to store the metadata in the registry.• A set of create, read, update and delete(CRUD) operations to manipulate the data

structure in the registry.Metadata:• Ownership and containment.• Categorization• A logical referencing mechanism.Operations:• Authentication for operations that change the registry.• Open access for read and query operations.

2. How information in UDDI can be conceptually categorized?

Using predefined categories:• Businesses classification: Using the North American Industry Classification System

(NAICS)• Product and service classification: the Universal Standard Product and Services

Classification (UNSPSC).• Geographic location classification: the ISO 3166 standard

3. What are main mechanisms of Web services discovery? Briefly explain each of them. Which of them is mainly used in web services discovery?

There are 4 mechanisms in web services discovery:• Discovery through email, ftp, CD etc.• Discovery at the point of offering.• WSDL repository.• UDDI

In the first approach, the service provider sends the service description through email, ftp or CD to the service requestor in accordance to a previously agreed business partnership. This is a static and a very simple approach.

In the point of offering mechanism, the service description is downloaded from a formerly known list of services. This is an effective approach in statically settled business agreements. But it is neither dynamic nor does offer a wide range of choices for the service requestor.

The WSDL repository is a distributed approach where the service requestor searches in a wide range of distributed repository of service descriptions. This approach is much more dynamic.

The UDDI approach provides the concept of point to a service definition. The providers can define a taxonomical classification of their services, provide a new technical model, reference an existing technical model which might later be used by other service providers. The provider can change his service description without changing the UDDI reference.



The web services use the UDDI approach.

4. What are main data structures in the UDDI description? Explain briefly their roles.

The main data structures are• businessEntity:

• It describes an organization that provides web services.• It contains references to one or more businessService

• businessServices:• It describes a group of related Web service offered by a businessEntity.

• bindingTemplate:• It provides technical information necessary to use a Web services.

• tModel:

• It acts as generic container for any kind of specification

• publisherAssertion:• It defines a relationship between two or more businessEntity elements.

• Subscription (UDDI 3.0):• Itʼs used to keep track of changes of entities.

5. Which changes will appear in the businessEntity element after the invocation of the save_business operation for this businessEntity element for the first time?

• A new business key • A discovery URL• An operator name: The name of the custodian who give it the key• An authorized name: the name of the entity who published the information.

6. Explain how major WSDL elements map into UDDI elements?



• Service interface -> tModel. As the service interface in the WSDL defines a reusable definition of a service it corresponds to the tModel of the UDDI. If the service interface definition contains more than one binding element then the reference to the service interface may include a pointer to a specific WSDL binding element.

• Service implementation -> businessService: The service implementation is defined by the WSDL service element which corresponds to the businessService element.

• Service location -> accessPoint: The web service location listed in the WSDL port element must be the same as the accessPoint element in UDDI.

7. What is tModel and what is its role in UDDI? Give an example of its usage.

A tModel is a generic container for any kind of specification.It is used to define the technical specifications for a service.Example of tModel:<tModel tModelKey=”...YahootModelKey...”>! ! <name>Yahoo! Business Taxonomy</name>! ! <description xml:lang=”en”>Yahoo! Business Taxonomy</description>! ! <categoryBag>! ! ! <keyedReference keyName=”Yahoo! category”! ! ! ! keyValue=”categorization”! ! ! ! tModelKey=”...sometModeKey...”>! ! </categoryBag>! </tModel>

8. How to describe our classification or identification schema in UDDI? Give an example.



To describe our classification we have to:1. Define one tModel2. reference that tModel in the categoryBag

Example:

! <tModel tModelKey=”...YahootModelKey...”>! ! <name>Yahoo! Business Taxonomy</name>! ! <description xml:lang=”en”>Yahoo! Business Taxonomy</description>! ! <categoryBag>! ! ! <keyedReference keyName=”Yahoo! category”! ! ! ! keyValue=”categorization”! ! ! ! tModelKey=”...sometModeKey...”>! ! </categoryBag>! </tModel>

! <categoryBag>! ! <keyedReference keyName=”Sporting and Athletic Goods Manufacturing”! ! ! keyValue=”33992”! ! ! tModelKey=”...NAICStModelKey...” />! ! <keyedReference keyName=”New York”! ! ! keyValue=”US-NY”! ! ! tModelKey=”...ISO3166tModelKey...”>! ! <keyedReference keyName=”Yahoo Business Taxonomy”! ! ! keyValue=”Business_and_Economy/Shopping_and_Services/Sports/! ! ! ! ! ! ! skateboarding/Deck_andTruck_Makers/”! ! ! tModelKey=”...YahootModelKey”>! </categoryBag>

To describe out identification we use the identifierBag. With that the users can search (discover) your business with a specific identifier like D-U-N-S number.

Example:

<identifierBag>! <keyedReference keyName=”DUNS”! ! keyValue=”00-11-1111”! ! tModelKey=”...D-U-N-StModelKey...” /></identifierBag>

9. Explain the difference between registry-based and index-based service discovery mechanisms.

Location: In registry-based approach all the service descriptions are published in a common registry. Whereas in index based approach the service descriptions are published at different locations.

static/dynamic finding: dIn registry-based approach, the service requestor has a static knowledge on the location of the registry. In index based approach the requestor should dynamically find for the location of several registries through some search operations.



Limitation: In registry-based approach the requestor is bound to the limit of the registry, whereas in index based approach the requestor is has no bounds as it can search through the entire range of options available.



Lecture 6: WS-Security.

1. What are the purposes of each specification?

• WS-Security: It defines on• how to include the security tokens in SOAP messages and• how to protect messages with digital signatures and encryption.

• WS-policy: Provide a framework for describing Web services Meta-information.• WS-Trust: It prescribes an interaction protocol to obtain Security Tokens Services.• WS-SecureConversation: It defines a security context with which parties can share a

secret key to sign and encrypt parts of messages efficiently.• WS-Federation: Provides a framework for federating multiple security domains.• WS-Privacy: Provides a framework for describing the privacy policy of web services.• WS-Authorization: Defines on how to exchange the authorization information among

parties.

2. What is the difference between symmetric and asymmetric encryption? Which one is more suitable for web services? Explain your answers.

Key: In symmetric key the same key is used on both the sender and receiver side to encrypt and decrypt messages. In asymmetric encryption the receiverʼs public key is used to encrypt the message on the sender side and the receiverʼs private key is used to decrypt the message on the receiver side.Speed: The asymmetric encryption is much slower than symmetric encryption technique.

Asymmetric encryption is suitable for web services. This is because the usage of different keys ensures authorization.Authentication and message integrity can be ensured by digital signatures which implements asymmetric encryption.

3. What is a security model for web services? What are its purposes? What are the elements of this model?

The security model provides a model for a secured transaction of messages between the service requestor and the service provider.A third entity name security authority comes into play in order to provide security token for the requestor.



Its purposes are• To provide an abstract model that combines all the existing security mechanisms.• To provide security tokens like the certificates to the service requestors.• To provide authentication, authorization and message integrity.

Elements of this model are:• Security Token Service• Service Requestor• Service Provider• Security Tokens• Claims• Policy

4. What are security requirements for WS?

1. Privacy: The transmitted information has not been captured or passed to a third party without your knowledge.

2. Integrity: Guarantee message not changed during the transmission.3. Authentication: Guarantee the identity of the sender and the receive..4. Authorization: manage access to protected resources.5. Non-repudiation: Guarantee that the message sender cannot deny having sent it.6. Availability: Guarantee that the system operates continuously.

5. What is single sign-on? How is it achieved in Kerberos security infrastructure?

The user provides his authentication information namely user id and password only once to access several applications within a certain interval of time. This is called as single sign-on.

Kerberos achieves Single sign-on as follows1. The sender sends the user id and password to the KDC and gets a Ticket Granting

Ticket (TGT).2. The sender now again sends the TGT to the KDC and gets a Service Ticket (ST).

! ! The ST contains• the senderʼs ID• senderʼs session key and• the TGT expiration time.

3. The sender send his/her message authenticated through the ST until the expiration time, without using his/her username and password for each transaction.

6. What is WS-Trust? Why do we need WS-Trust? What is the difference between the usage of PKI and Kerberos in WS-Trust?

WS-Trust prescribes an interaction protocol to obtain security tokens from security authorities.We need WS-trust in order to establish trust relationships between security authorities. (WS-Federation)

Differences between PKI and Kerberos• In Kerberos, we request for the username for ourselves. In PKI, we request for the

certificate of others.



• In Kerberos, the token type is TGT where as in PKI the token type is certificate.

7. What is WS-SecurityPolicy and where is it mentioned?

WS-securityPolicy is a domain-specific language to represent policies for WS-Security.For example, you can describe your desired policy in such a way that a signature is required on a particular element and that a particular element must be encrypted.

WS-SecurityPolicy will be usually mentioned under the WS-Policy of the Web services description (WSDL) file.

8. What is WS-SecureConversation? What are the 3 ways to achieve it?

It defines a security context with which parties can share a secret key to sign and encrypt parts of messages efficiently.

The Security Context Token can be created in the following ways.1. A security token service issues the security context token.2. One of the communicating parties issues the security context token.3. Both the communicating parties negotiate with each other and agree on the security

context token.

9. Give a basic syntax of WS-Security.

<wsse:Security! xmlns:wsse=“http://schemas.xmlsoap.org/ws/2003/06/secext”> ! <Signature xmlns=“http://www.w3.org/2000/09/xmldsig#”>! </Signature>! <EncryptedKey xmlns=“http://www.w3.org/2001/04/enc-enc-enc#”>! </EncryptedKey>! <wsse:UsernameToken! ! xmlns=“http://schemas.xmlsoap.org/ws/2003/06/secext”> ! </wsse:UsernameToken></wsse:Security>



http://schemas.xmlsoap.org/ws/2003/06/secext


http://www.w3.org/2000/09/xmldsig#

http://www.w3.org/2000/09/xmldsig#

http://www.w3.org/2001/04/enc-enc-

http://www.w3.org/2001/04/enc-enc-



Lecture 7: WS-Coordination and Transaction

1. What are coordination controllers? How do they resolve the differences between the requests from various clients?

Coordination controllers are components that reside in the service provider. Their main task is to resolve the requests from various clients and thereby to maintain the context for each client request separately.

They achieve this by creating a separate copy of the WS objects for each request of each client, thereby maintaining the individuality in request processing.

2. Explain the need for coordination from internal and external service perspectives.

Internal Perspective:• Complex procedures: Client must be able to execute complex procedures in

appropriate order.• Maintain the context information: Client must be able to maintain the context

information in order to pass it from one operation to other.• Complex internal logic: An internal logic of the client is more complex.

External Perspective:• Order: Ensuring order of operation.• Conversation: Conversation rather then simple invocation.

3. What are main forms of interaction defined by WS-Coordination?

Activation: The participant requests the coordinator to create a new coordination context.Registration: The participant registers itself as a coordination protocol participant with the coordinator.

Protocol specific interaction: The coordinator and the participant exchange messages that are protocol specific.

4. What is Atomic Transaction in Web Services? What is Business Activity in Web services? What is the difference between them?



The Atomic Transaction is a protocol that make sure either the entire set of operations within the transaction completes successfully or the entire transactions is rolled back as if none of it ever happened.It can use Durable two-phase commitment or volatile two-phase commitment.

Business activity is a protocol that allows long running transactions to be used without worrying about locking resources.In business activity each and every web service call is a complete and independent transaction that will be committed.It provides a compensation mechanism through which corrective steps are taken to rollback a transaction instead of actually rolling back.

• Completeness and dependency: In atomic transaction each and every steps are executed incrementally and finally the entire transaction is either committed or rolled back. In BA each and every service call is considered as a transaction and are either committed or rolled back.

• Resource lock: In atomic transaction, as the resources are utilized until the commit or rollback is made the resources remain locked. Whereas in BA as each and every step is a transaction the resources remain unlocked.

• Rollback: Atomic transaction allows the rollback mechanism whereas BA does not allow roll back. Instead compensation mechanism is executed.

• Instead the commit of AT, BA has complete• Instead the rollback of AT, BA has compensate

6. What is Coordinatorʼs chaining in web services coordination?

Each coordinator may have different roles: one as participant, other as coordinator. The participant just forward, when the coordinator may ensure some activation, registration and so on.So each coordinator may have two roles, and then we can have such chain of coordinator.

7. What is a way of publishing coordinator protocols?

Coordination protocols can be published as tModels. These tModels can be associated with a specific binding template.



8. Draw a WS-Coordinator flow between two web services using a central coordinator. Show required portTypes in your flow.

9. What are the relations between WS-Coordination and WS-Transaction?

• WS-Transaction use WS-Coordination: WS-Coordination has some specific protocols for coordination. These protocols are being used by WS-Transaction. Thus naturally WS-Transaction is built upon WS- Coordination.

• Combination: WS-Coordination and WS-Transaction can be used in combination to achieve transactional semantics.

10. What is the compensation mechanism? Why and when is it used?

Compensation mechanism is the process in which corrective steps are taken in order to achieve a roll back effect in case of an aborted transaction.

In Business activity, when a transaction needs to be aborted, the coordinator sends a compensate message to each participant. This allows the participant to take whatever action it deems necessary to make up for previously taken (and committed) actions.

11. What is a coordination context in WS-Coordination? Which components it has and where is it included? Give an example.

Coordination context is a data structure used to mark messages belonging to the same conversation.



It contains a unique identifier that will be attached along with each and every message belonging to the same conversation.It has the “context identifier” and “expires” components.

<wscoor:CoordinationContext>! <wsu:Identifier>id2</wsu:Identifier>! <wsu:Expires>2009-10-20</wsu:Expires></wscoor:CoordinationContext>

12. Give a example of WS-Coordination flow between two Web Services when distributed coordinators are used (you may present the flow graphically)

13. What are main abstractions of WS-Coordination? (Why use it)

WS-Coordination defines a coordinator that keeps track of and manages the various resources (Web Services) involved in multi-party operations.

The abstraction of the WS-Coordination are:• A coordination protocol: a set of rules governing conversation• A coordination type: a set of coordination protocols logically related to each other• A coordination context: a data structure used to mark messages belonging to the

same conversation.



The operations are activation, registration, and protocol-specific interactions.



Lecture 8: WS-Composition

1. What is an abstract process in BPEL? What is its purpose? How it differs from other processes?

A business protocol specifies the order in which message between partners need to be exchanged.An abstract process specifies the business protocol from the perspective of a partnerʼs internal business process rather than their implementation details.

Its purpose is to just specify the exchange of messages between the partner links and their potential sequence without any implementation.

In abstract processes the complete implementation details are not available whereas in executable processes the complete implementation details are available.

2. When and how in BPEL a compensation handler for a give scope in BPEL becomes active?

A compensation handler becomes active once when the corresponding invoke activity or scope gets completed successfully.

3. What is the idea of correlation set in BPEL4WS? Where is it useful? Give an example.

Correlation set is the combination of two or more keys in order to correlate messages to a single process instance.

It is useful in situations where the single process has to process multiple similar requests from various requestors.

For example For the same process instance of process order, if a customer is submitting another purchase order before the previous purchase order gets processed, then the customer ID is alone not enough to establish uniqueness.In such a case we need to have the order ID as well.

Therefore this notion of correlation set allows us to identify a particular instance of processes.

4. What is the difference between WS-Coordination and WS-Composition?

• Composition is about the internal implementation of web services, whereas coordination is about the external or conversational aspects of web services.

• Composition specification is for consumption of Web service middleware which automates execution of services.

• Composition is about the automating communication and making decision, while coordination is just about the conversation between the web services.

• The conversation controller could be unaware of whether it is dispatching messages to a basic or a composite service.



5. What is orchestration in Web services? Which orchestration models are supported in BPEL for WS?

Orchestration is the arrangement or ordering of web services to be executed in a particular order in order to achieve particular business logic.

BPEL4WE support activity hierarchy model.

6. What happens when a fault handler in BPEL throws a fault itself?

If the fault handler throws a fault by itself, then this fault will be caught by the next higher enclosing scope. This applies to explicitly thrown and unexpected faults in the fault handler.

7. How a correlation of messages with the process instance is done in BPEL?

Correlation of messages can be achieved through the use of correlation sets.

8. What are the elements of the WS-Composition middleware?

• Composition development environment.• Composite schema.• Composition run-time engine.• Composite service execution data.

9. Which WSDL extension is introduced in BPEL? Why? Give an example.

PartnerLinkType: Contain one or two roles, which define the responsibilities of each side of the conversation.

Example:

<plnk:partnerLinkType name=“purchaseOrderPartnerLinkType”>! <plnk:role name=“seller”>! ! <plnk:portType name=“pos:poSubmissionPortType”/></plnk:role> </plnk:partnerLinkType>

Property: is a named, typed data element and itʼs used to identify BPEL process instance.The property value is extracted from an instance of a WSDL message by applying a message-specific XPath expression.

Example:<wsbp:property name="customerID" type="xsd:ID"/>

PropertyAlias: A propertyAlias defines the relationship between the property and the data field in the message.

Example:<wsbp:propertyAlias propertyName="customerID" part="purchaseOrder“ messageType="pos:poSubmissionRequest" query="/billTo/id"/>

10. What are the 2 possible areas where concurrency can be achieved?



Flow: Using the fork activity, multiple processes can be executed in parallel.Event Handler: It can process multiple events of the same type in parallel.

11. Explain the relationships between partnerLinkType, partnerLink and PortType in BPEL.

PartnerLinkTypes contain on or two roles. This role refers to a WSDL portType. PartnerLinkType is contained by the partnerLink.

12. How a dynamic partnerLink binding can be done in BPEL?

For the dynamic binding of partnerLink, BPEL uses endpoint references. Itʼs defined as a mechanism to dynamically identify and describe service endpoints and instances.

It contains:• The address of a service endpoint• Optional reference properties• Optional identifications• Optional policies



Lecture 9: Stateful resources

1. Justify a case when notification broker is useful. What additional operation(s)notification brokers supports if we compare to ordinary notification providers?

Consider a case where a publisher is either not interested or does not have a provision in keeping track of notification consumers. In such a case, the publisher can register itself to a notification broker and send in all the notification messages to the broker. Later these notification messages can be sent to the appropriate consumers.

Notification brokers support the additional operation of RegisterPublisher which allows the notification publishers to register themselves before publishing any messages to the broker.

2. Explain what is Implied Resource Pattern?

It is a set of conventions on Web Services technologies.

It refers to the mechanism which associates the resources with execution of message exchanges in Web services.

The conventions allow the state of a resource to be defined and associated with the description of a web service interface.

The term implied is used because the identity of the resource is implied by the context of the message and its association with an end point reference and not directly to the signature of the message.

3. What is the difference between resource properties and reference property in WS-Resource?

Resource property represents atomic element of state that can be read and written.A set of resource property elements are gathered together into a resource property document.Reference property is used to access a particular WS-Resource that has particular state information, which the web service is interested in.

4. What are Ad Hoc topics? How are they implemented? Why should they be used with caution?

Ad Hoc topics are more specific topics that cannot be categorized under any of the existing topic spaces.The properties are:

• Dynamic adding: They are generated and added dynamically.• Self adding: These Ad Hoc topics will be added in to the Ad Hoc topic space itself.• child topics: They can contain child topics.

It can be implemented using the following namespace URI: http://www.ibm.com/xmlns/stdwip/web-services/WS-Notification/adHoc.

This should be handled with caution because the subscriber does not know beforehand about it or about the topics mentioned with in it. It should be used only for dynamic topics.



http://www.ibm.com/xmlns/stdwip/web-services/WS-Notification/adHoc




5. Explain many-to-one relationship between Web services and WS-Resources. When is it appropriate?

In many-to-one relationship a single WS-Resource will be associated with multiple web services.

It is appropriate in situations where a load-balancing is necessary. This allows the scaling of web services to handle enormous amount of incoming messages to be handled efficiently.

6. What is a singleton-pattern in WS-Resource?

Its the one-to-one relationship between a WS-Resource and a web service.

7. What is endpoint reference in WS-Addressing? What does it contain?

The endpoint reference in WS-addressing is an XML serialization of a network-wide pointer to a Web service.

It contains• A transport specific network address of a web service.• Optionally contain additional metadata about the web service.

8. What is the difference in immediate destruction and scheduled destruction with when time of destruction is in the past?

Immediate destruction is a synchronous operation and scheduled destruction with when time of destruction is in the past is an asynchronous means to achieve immediate destruction.

9. Which kind of resources can be terminated only by immediate termination mechanism? Why?

Resources that have their termination time set to xsi:nil can only be terminated immediately. This is because of the fact that they have infinite life time and therefore they cannot be scheduled to be terminated in the future.

10.What are 2 main approaches in identifying the WS-Resource?

URI encoding: In this approach, a specific URI value is attached along with the end point reference of the web service.

Reference Property: through the stateful resource identifier.

11. What is resource property document? How and where is it described?

It is an XML document contains the resource property elements grouped together.It can be queried by the client path applications using XPath query.This is described using the WS-ResourceProperties.It will be described as an XML schema document.



12. How service requestor can examine or interpret the content of “Reference Properties” elements of a WS-Resource endpoint reference?

It can examine the content of the resource property document using the following resource properties operations.

• GetResourceProperty: It is a simple get by name method to retrieve the value of a WS- Resource property.

• GetMultipleResourceProperties: It is also a simple get by name method that retrieves multiple resource properties with single message exchange.

• QueryResourceProperty: It allows us to use query expressions like XPath queries to get the values of resource properties.

• SetResourceProperty: This is to manipulate the resource properties document. It includes the following components:

• Insert• Update• Delete.

13. In WS-Resources stateful resource(s) is/are assciated with Web service(s). Explain what this association means.

The web service provides a platform for sending messages to resources.

The stateful resources represents an identifiable unit of state information.

The relation between them could be:• One to many: A web service is responsible for processing messages related to many

WS-Resources• One to one: one Web service, one stateful resource• Many to one: Ws-Resource are associated with many web services.

14. How can a service requestor compare two stateful resources based on content of the reference properties? Explain your answer.

They canʼt. The service requestor should not examine or attempt to interpret the contents of the reference properties.For service requestor, the content of reference properties is opaque.



Lecture 10: Semantic Web Services

1. OWL-S profile represents two aspects of service functionality: information transformation and state exchange. Explain what does it mean? Give a simple example.

2. How grounding of service is proposed in OWL-S?

Grounding of service in OWL-S is proposed through the WSDL language. OWL-S concept of grounding is generally consistent with the WSDLʼs concept of binding.

Mapping OWL-S to WSDL:• Atomic process <-> operation• Input/output message <-> message• Type of OWL-S input/outputs -> WSDL types

This can be achieved in one of the following ways• Referring the OWL-S elements in to the WSDL by using the owl-s-parameter• Referring the WSDL elements in to the OWL-S by using the WsdlGrounding class.

3. RDF document is a collection of statements each of which is expressed as a triplet. What are components of the RDF triplet?

The components of a triplet are subject, predicate and object. For example the URI www.google.com/index.html was created by George can be represented in a triplet as followsSubject - www.google.com/index.htmlPredicate – created byObject – George.An entire triplet forms a resource.

4. Which components constitute the top level service ontology in OWL-S? Which questions about a service each of them answers?

The top level service ontology in OWL-S is composed of• Service Profile – what the service does?• Service Model – how the service works?• Service Grounding – how to access the service?

5. What are the relations between current web, web services, semantic web and semantic web services technologies?



http://www.google.com/index.html




The current web technology does not allow us to find services dynamically. So, the usage of web services enables the client applications to find relevant services.

Incorporating semantics in to the web services will enable multiple web services to talk among themselves and decide on how to achieve the goal of a particular business process.

6. Show layers and associated web services technologies of semantic web stack.

7. Why do we need semantic web services? Give an example of their usage.

We need semantic web services for the following reasons:



1. Service location: syntactically different but semantically similar terms can be used by the service provider and requestor for the same service.

Eg: If a service provider provides a service named Payroll Processing and the service requestor looks for a service name Employee Payroll Processing then adding semantics will allow the service requestor to use the Payroll Processing web service.

2. Service invocation: constructing correct messages based on the published service interface.

Eg: Consider the scenario where there are 2 providers offering Payroll Processing service that takes different input parameters. Then adding semantics to the service descriptions enables the service requestors to decide on what is the appropriate service to be invoked.

3. Results understanding: interpreting the results of service invocation.

Eg: As in the above example for service invocation, adding semantics to the service result enables the service requestor to decide on which is the appropriate service to be invoked to get the desired result.

4. Service composition: constructing complex services by combining the results of multiple services.

Eg: Consider a service called Create Applicant Profile that creates a complete profile of a student/employee by getting his/her information from other web services like that of university transcript information, work experience information etc. In such a case the output from multiple web services needs to combined together to produce the applicant profile. Adding semantics will enable the web services to choose the correct web service to be invoked for each of the applicant.

8. What is OWL-S? (2010 - 03)

OWL-S ontology is a language for describing services. It provides a standard vocabulary that can be used together with the other aspects of the OWL description language to create service description.



PWS Exam Questions 2005 - 2010 V1.0

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