Importance of Web Services - Assignment Example

XML Web Services and Service Oriented Architecture By Date Table of Contents XML Web Services and Service Oriented Architecture 1 By 1 Table of Contents 2 Introduction 3 Importance of Web Services 4 Mechanisms for the Discovery of Web Services 5 Service Oriented Architecture 7 SOAP 9 WSDL 10 REST 10 Solutions for Developing Web services 11 Conclusion 12 Bibliography 13 Introduction In the industry of computer software, specifically, internet based applications; web services have been given considerable importance. The main reasons are its support for important non functional requirements such as reusability and platform independence – where these services can be accessed and utilized irrespective of host’s operational environment (e.g. operating system, underlying IT infrastructure). Web services contributes to interoperability by promoting the use of consistent and standardized interfaces and hence matching with underlying infrastructure’s interfaces of an enterprise’s existing IT solutions, consequently making the integration of existing and new services easy and enhancing the flexibility of the overall system (Schelp et al, 2009). In addition, the web services are basically the components that exchange information and messages with other software components using common web standards such as HTTP. The messages are based on XML (Extensible Markup Language). Web services allow the client’s applications to perform certain simple and complex operations, such as checking account balance online, or maintaining the flow of processes such as CRM (customer relationship management) or enterprise resource planning (ERP) systems. Web services support interoperability and are independent of hardware, programming language, and operating system. The main reason is that, web services are based on the utilization of open standards such as HTTP, SOAP and WSDL, for communication and transport. It may allow applications developed in different programming languages and being executed on different operating systems to flawlessly communication and exchange data over Internet using Web based technologies (Erin Cavanaugh, 2006) Importance of Web Services A web service is an interface to a functional component that is accessible over a network or internet development using standard Internet technologies such as HTTP, XML, SOAP and WSDL. For a software component to be known as a ‘web service’, the only requisite is that it must be able to send and receive messages for access and communication aforementioned set of standard Internet protocols. From development point of view, the application code contains all the logic that implements the functionality of business such as listing all the categories of books, adding a book to a shopping cart, paying for books etc. The Service consumer receives incoming services over HTTP (Hypertext transport protocol) using SOAP (Simple Object Access Protocol) messaging. The service proxy interprets those requests into calls into the application code. So a service can be consumed irrespective of development platform e.g. JAVA, C#. Interoperability is the major advantage that makes web services special than other web application technologies. In this way, the solutions that are based on Java and Microsoft Windows-based solutions have no difficulty to get integrated, as it was in the case of other distributed technologies such as CORBA, COM/DCOM, RPC, RMI etc (Doug Tidwell et al, 2001). Web Service have been established as an alternative and powerful paradigm that offer certain advantages over other distributed technologies like RMI, .NET Remoting (COM/DCOM), CORBA etc. The traditional distributed technologies use a specific model to reference objects to be implemented on client side as well as on the server side so hindering interoperability. On the other hand web services use a standard model of defining a service at the ‘server only’. Where the service can be invoked anywhere and invocation can be done with the help of the client from any place. Web services have provided the solution for various problems that previous distributed technologies have faced such as those technologies needed the creation of ‘Sockets’ for communication so programming complexity was much more than it is for web services. Previous Technologies are also tightly coupled with respect to end points e.g. CORBA requires compatible ORBs at each endpoint, similarly COM/DCOM requires Windows on each point for the functioning of this paradigm.web services support platform heterogeneity and allows communication as well as access of services in language and platform independent manner (Rohit Dhand, 2009, P. H. Phu et al., 2005). Because of the use of common standards such as SOAP over HTTP protocol for the communication by web services technologies, it is very less costly to implement web services as compared to other proprietary solutions such as B2B and EDI (Enterprise Data Interchange). Also, it is possible to implement web services using protocols other than SOAP HTTP making it possible to implement the web services that may be customized according to specific requirements e.g. it is possible to implement web services using File Transfer Protocol (FTP). As compared to previous technologies, web services support loose coupling. It makes the application adaptable to changes as new services can be implemented and composed to satisfy new requirements and it also reduces development time (JAVA Beat, 2008). Mechanisms for the Discovery of Web Services Once a web service have been developed, some mechanism must be defined through which clients who want to consume that service, must be able to discover, which services are available to satisfy their requirements . So the mechanism, known as Web service discovery, deals with publishing and discovering the web service using a service description defined in WSDL (Web Service description Language). Discovery mechanism enables clients to discover that which services are available and where the description of service (WSDL) is located. The mechanism of discovery of web services is not only a step but it is a complete process involving multiple entities and states. Service consumer may not be having sufficient knowledge of SOAP or XML in this case service discovery becomes difficult (Shrabani Mallick et al., 2010). UDDI (Universal Description, Discovery and Integration) is a standard mechanism that is basically uses to aid the service consumers who are searching for the WSDL of certain services that describes them. Information is maintained in UDDI registry in the same manner as in a telephone directory i.e. It contains “white pages” “yellow pages”, as well as a “green pages”- that maintain information about services such as business search, topical search and service type search respectively. It may allow developers to find a service using different criteria’s. The UDDI standard involves a web service known as the UDDI Business Registry (UBR), a directory, where the service providers can register and publish the description of their services. It allows consumers to query and discover the needed services to access n integrate it in their applications (James Kao, 2001) In addition to UDDI there are certain approaches that can be used to discover the web services. Standardized portals which use certain crawlers for gathering services can be used. Also, web search engines can be customized to confine the search to service’s WSDL e.g. Google and Baidu allows to restrict the search to certain type of documents so this flexibility can be utilized to search for the WSDL of certain services (Daniel Bachlechner et al., 2006). Service Oriented Architecture A service-oriented architecture is a paradigm in the world of web/ internet based online applications which allows for the use of readymade services (available on a network such as World Wide Web) that can be access and integrated in any application to satisfy a certain requirement. Developing a services oriented solution involves the development of an application also known as services so that can be composed with other applications at run time according to the requirements. Following diagram describes service oriented architecture: Figure 1: Service Oriented Architecture, Image Source: http://java.sun.com/developer/technicalArticles/WebServices/soa2/soa2.pdf In its simplest form, service oriented architecture involve different component. A service provider, it can be a software component or a mainframe system that serves the service request. The service provider basically registers the contract of the service in the registry for access by service consumers. A service consumer ( an application, a service, or some other type of software module) who queries UDDI to discover the desired service, and a UDDI registry, which is a directory of services which contains certain information about the services such as which services are available and where the description (WSDL) of certain service is located. In addition there is also a component that is not required all the time, known as service proxy. It may not be required as service consumer developer may write certain code for accessing the service directly. Playing its part, a service proxy allows a service consumer to access a service by calling a function on proxy. The service proxy then returns the contract and reference to the service provider in the registry (Ed Ort, 2005). Typically there are certain principles that must be followed when implementing an application based of Service Oriented Architecture (SOA). Services in SOA must define a standardized service contract that may be used to access the service. Services in SOA must support loose coupling and must be accessible at certain level of abstraction, hiding certain low level details. In addition SOA requires some other principles to be followed while developing an SOA solution; these principles are service granularity, service usability, service autonomy, service statelessness, service discoverability, and service composibility (Cape Clear Software Inc, 2004). Web services and service oriented architecture are related in a way that services can be used to implement a service oriented solution. By nature, service oriented architecture is an architectural style, whereas web services are technology to implement service oriented as well as some other architectural style such as Grid computing. It is possible to use SOA and web services in combination but it doesn’t mean that they are dependent. In the same way, while Web services provide the basis for the development of a service oriented solution but it is not compulsory for to represent the SOA principles. If web services are stateless, it doesn’t means that they are dependent on SOA, so are using its principle of statelessness, but in some cases web services have no need to be stateless but it totally depends on the architectural style of the application in which that service is going to be integrated (Latha Srinivasan et al, 2005). SOAP SOAP (Simple Object Access Protocol) is an XML-based protocol being used for communication for the purpose of remote object invocation. The main purpose of SOAP is to allow distributed applications to communicate over HTTP for accessing services in a platform independent manner. SOAP protocol was basically developed to cope with the problems faced by HTTP that it was a protocol mainly used to transport files from server to client, to develop more complex applications it was not enough. SOAP serves its purpose in this regard that it adds a set of headers and payload, which can be transported over HTTP which allows communication between complex applications over internet. So in this way SOAP adds interoperability and ease of integration in a service oriented solution (Jack Koftikian). SOAP does not provide a programming model or implementation specific details for an application. But it just provides a mechanism for the application to communicate with the web services using SOAP envelope. SOAP envelops contains two elements: a header and body. Header may provide information about authentication and encoding of data whereas body contains actual content of the message that is being communicated (Hartwig Gunzer, 2002). WSDL WSDL is the XML based description of a web service which basically serves as an interface to service. WSDL describes the services that are accessible by service consumer and are used to create the SOAP messages that may be exchanged between service provider and consumer to access the services. Like IDL (Interface Definition Language) file in CORBA or Remote Interface in a Java RMI implementation it defines the interface of a web service. A WSDL file provides certain information about the service such as types, messages, port types, binding and services. It specifies the data types relevant for sending and receiving messages, the data that must be communicated in the messages, the operations of the service and some other information related to transportation mechanism (Hartwig Gunzer, 2002). REST Representational State Transfer (REST) is an architectural style that was introduced for building complex and large scale hypermedia applications. REST architectural style is based on certain principles such as there must be a URI(Universal resource Identifier) through which resources that are exposed by the service, may be identified. It may allow for global addresses for the discovery of services and resources. Certain operations such as PUT, GET, POST, and DELETE are always used to manipulate the resources. PUT allows creating a new resource, DELETE allows deleting any resource, GET gets and returns the information about the current state of a resource and POST shifts the resource in some other state. Self-descriptive messages about the resources are specified and metadata about the resource is available which helps in detecting transmission errors and performing authentication or access control. Every communication with a resource exposed by the service must be stateless so that request messages to access those resources must transfer the state of the resources explicitly and it can be done using several techniques e.g., URI rewriting, cookies, and hidden form fields. REST web services also expose some advantages such as it requires a very little effort to build REST web service and it can be tested using an ordinary web browser without any need of developing customized client software (Cesare Pautasso et al., 2008). Solutions for Developing Web services As the markets have expanded rapidly, to develop robust web applications, Microsoft have addressed this issue by introducing a set of technologies known as WS -* architecture for the development of web services. Holding on to the simplicity of web services, these standards allow to build and develop large scale complex applications based on web services. The WS-* stack introduced by Microsoft offers certain strengths over other solutions such as a significant feature of the WS-* architecture is composability. Composing different protocols (security, reliable messaging, attachments, discovery, policy, policy attachment etc.) makes it possible to incrementally develop web services solutions that satisfying these requirements in an interoperable manner. The requirements addressed by WS-* protocol stack, in combination, may allow to address higher-level functionality commonly required by distributed applications. In this way, to reduce the complication and development cost of complex applications involving multiple functionalities, the WS-* specifications can be utilized either independently or in combination with one another. A specific WS specification can be used in order to apply certain functionality, solving immediate need. With the emergence of new application requirements, new specifications can be utilized where as web service developed using previously used specifications allows backward compatibility (Payam Shodjai, 2006). Even the fact exists that web services promote platform and programming language independence but to gain the maximum advantage, JAVA technologies are most suitable for developing web services as compared to other technologies. Because JAVA is open source so program written in JAVA are pretty portable and interoperable and this characteristics of JAVA programming fits together very well with web services in order to enhance the interoperability. JAVA 2 Platform, Enterprise Edition (J2EE) 1.4 is a platform which consists of all core technologies that are introduced by JAVA for developing the web services. The technologies introduced by JAVA are compatible to be used with XML standards for web services such as SOAP, WSDL and UDDI. In addition as compared to other technologies web service developed in J2EE 1.4 offer better resource pooling and transaction management (Ed Ort, 2005). Conclusion Web services have provided us with a very robust technology to develop internet based applications that may cope with rapidly changing requirements. The main reason for increased popularity is the capacity of web services technology to accommodate non- functional requirements such as reusability, flexibility and interoperability. In addition, web services also allow the services written in different languages to integrate with the applications developed in some other languages thus promoting platform independence. Web service use different XML based standards such as SOAP, WSDL, and UDDI that may ease the communication, discovery and publication of the services. Service oriented Architecture is an architectural style that allows a cost effective and faster development of applications by composing services. It typically involves a service provider that execute the service requests, service consumer, who request to access the services offered by the provider and a UDDI registry where services are registered and discovered. SOA and web services are related in the way that Web services can be used to develop an SOA based application but it doesn’t mean that SOA and web services are mutually dependant. Different proprietors have introduced certain technologies for the development of web services such as Microsoft allows the development of a web service using asp.net , WCF, WPF etc and also have introduced WS-* stack that specifies different protocols that can be used to address different aspects of web services such as security, reliable messaging, addressing, policy, policy attachment and discovery. On the contrary JAVA has introduced J2EE 1.4 which is a core set of technologies for developing web services. As compared to other technologies, JAVA programming fits together very well with web services in order to enhance the interoperability. Bibliography Schelp, J., Aier, S, 2009, SOA and EA – Sustainable Contributions for Increasing Corporate Agility. In Proceedings of 42th Hawaii International Conference on Systems Science (HICCS-40). IEEE Computer Society Press, Los Alamitos (2009). Doug Tidwell, James snell, Pavel Kulchenko, 2001, Programming Web Services with SOAP, O’reilly publishers, ISBN: 0-596-0095-2. Phung Huu Phu, Myeongjae Yi, 2005, A Service Management Framework for SOAbased Interoperability Transactions, In Proceedings of the 9th Korea-Russia Intl.symposium on Science and Technology (KORUS2005, IEEE Press), Novosibirsk, Russia, pp. 680–684. Rohit Dhand, 2009, Web Services: A Trend Shift from conventional Distributed Computing Model, in proceedings of second International Conference on Computer and Electrical Engineering (ICCEE’09) Shrabani Mallick, D.S. Khushwaha, 2010, LWSDM: Layered Web Service Discovery Mechanism, Advanced in Information Sciences and Service Sciences, volume 2. Cesare Pautasso, Olaf Zimmermann, Frank Leymann, 2008, Restful Web Services vs. “Big” Web Services: Making the right Architectural Decision, International World Wide Web Conference Committee (IW3C2), Beijing, China. James Kao, 2001, Developers guide to building XML based Web Services with JAVA 2 Platform Enterprise Edition (J2EE), Sun Microsystems Inc. Daniel Bachlechner, Katharina Siorpaes, Holger Lausen, Dieter Fensel, 2006, Web Service Discovery – A Reality Check, 3rd European Semantic Web conference (ESEC’06), Budva, Montenegro. Ed Ort, 2005, Service Oriented Architecture and Web Services: Concepts, Technologies, and Tools, Sun Microsystems. Erin Cavanaugh, 2006, Web Services: Benefits, Challenges, and a unique Visual Development Solution. 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