XML Web Services and Service Oriented Architecture - Assignment Example

Technical Report XML WEB SERVICES AND SERVICE ORIENTED ARCHITECTURE 1. Importance of web services for the development of web based solutions to meet today’s business needs. Generally, a web service is the software component that enables distributed computing using one or combination of web technologies such as SOAP or Simple Object Access Protocol, WSDL or Web Services Description Language, and UDDI or Universal Description, Discovery, and Integration. It provides businesses the advantage of offering their product, services through the web, globalized, and sells beyond geographical boundaries thus they can expand and grow at a faster pace (Kumar, 2004, p.8). It is commonly considered as a family of technologies that can connect systems, businesses, and customers over the Web (Chen et al, 2003, p.137). Traditionally, before the introduction of web services, the Internet was mostly use for business-to-consumer transactions and limited communication or interoperability between disparate systems, incompatible applications, and proprietary communication protocols. However, due to the introduction of XML or eXtensible Markup Language, which is a text-based data description language capable of transporting data independent of networking protocols and operating system attempts were made to represent business data using the language. The result was interoperability between web applications without significant integration and development effort. This opportunity further enable business automation and interaction between the service provider, requester, and broker (ibid p10). In order to understand the importance of Web services fully, one must be familiar with the requirements of distributed computing and the Internet. Distributed computing allow applications to run on two or more computers in a network thus it requires high scalability, easy deployment and update, and effective data security such as protecting sensitive information, authenticated access, and securing transactions (Ullman 2005, p. 533). Similarly, the Internet increased the opportunity for larger and more complex networks of computers thus; it requires a more sophisticated distributed computing (Moroney & MacDonald, 2006, p.1054). Prior to the introduction of Web services, DCOM or Distributed Com, RPC or Remote Procedure Call mechanism, and COBRA were the dominant distributed technologies when there is a need to run applications on a network but they are difficult to interoperate, as they cannot support different platforms. Since the Internet is a complex network it therefore require a flexible distributed computing technology that can support a wide range of platforms, stateless, and firewall friendly such as HTTP, XML/SOAP, WSDL, and UDDI web services (ibid p.1052). Web Services is a mechanism that helps integrate business applications over the web. For instance, a business typically has different application systems performing specific tasks such as the system that manages material requirements planning and those that manages inventory control and distribution. One system may be managing customer orders while the other is specifically keeping track of customer information. Consequently, the process of sharing information between these systems and automating their interactions becomes essential in completing the required business process (Manes 2003, p.1). Web Service automates business process and opens the possibility for not only business to consumer transactions but business to business transactions as well. For instance, when a customer purchase a video player over the web, chain of events will be triggered automatically such as (Kumar, op cit): Charging the customer’s credit card Updating inventory and financial application of the web-based store Notification sent to distributor in case inventory is already below allowed level Update store database of new item purchase Record customer details and purchase for customer support. Web services enable business enterprises to run their business applications from outside third party service providers thus saving them time and resources of developing applications internally that will be managed by their own IT department. Moreover, it can give an organization a way to remarket existing intellectual content thus improving efficiency and reducing the cost of running their business (Clabby, 2002, p.3). Since Web services are technologies specifically designed to allow interoperability, platform, programming language, and transport independence, it fits well with emerging SOA applications that generally requires an independent, reusable, and adaptive services (Huang, 2007, p.27). Web services standards like SOAP, WSDL, and UDDI are proven useful in many applications such as connecting wireless clients to Web functions, providing interfaces to automated business processes, and bridging different software domains (Jeckle & Zhang, 2003, p.195). 2. Available mechanisms for discovery of a web service Web services is more than just distributed computing since its capabilities can be enhance by adding features such as discovery of its interfaces and supported user behaviour and requirements. For instance, WSDL contains information about the interface and semantics of how to call a specific Web service such as interface information describing all available functions, data type requirements, the protocol to be used, and the address of specific Web service (Nagappan et al, 2003, p.203). Generally, Web services need to discover other compatible Web services before they can interact with each other and do their business (Sahai & Graupner 2005, p.21). For instance, UDDI, a group of web-based registries that contains information about a web service provides universal description and discovery information. It help potential users in searching of information about web services by providing service requester information about who, what, where, and how to interact with specific Web service (Etoh, 2005, p.270). Each type of information in the UDDI registry is logically organized into pages – white, yellow, green - like a phone directory as shown. Figure 1- UDDI Web Service Discovery (Source: Network World, 2007) Web service discovery occurs in the following sequence: Web service requester or the one that is in need of a Web service searches the service registry. If the requester found the registry, it will then look for service description commonly written in Web Services Description Language or WSDL and note the information on who, what, where, and how to interact with specific Web service The requester then use this information to access the Web service provider. Allowed with access, the requester then invoke the specific service. An alternative to the above global registry approach to Web service discovery is WSIL or Web Service Inspection Language. WSIL provides a ‘business card’ approach while using Web conventions like “HTTP GET” to help users find the service. WSIL publishing is a discovery mechanism that published plain XML document containing references to existing service description documents such as a UDDI registry or another WSIL document, which in turn may link to another WSIL document. This Web service representation chain, as shown below, may link through multiple levels until the service requester found the desired service (Zhang & Cai, 2007, p.65). Figure 2 - Example service description document chain (Source: Zhang & Cai 2007) Based on iterative search technique, WSIL provides linkages to other published services and typically work following the service discovery sequence below (ibid p.70). Requester find the location of starting WSIL document or the ”supply.wsil” in the above example. Requester then perform the search for appropriate WSIL document Select a link and launch content of the selected WSIL document until it found the service. 3. Key features and principles of Service Oriented Architecture or SOA and the relationship between SOA and Web Services 3.1 Service Oriented Architecture or SOA features and principles SOA is software architecture with functionalities that can support, manage, coordinate and improve business processes. The fundamental idea behind SOA is to allow communication or exchange of messages between Web services. The following are the guiding principles and features of SOA (Tarkoma, 2007, p.107). The SOA guiding principles include: a. Reuse, granularity, modularity, composability, componentization, and interoperability b. Compliance to common and industry specific standards c. Identification, categorization, provision, delivery, monitoring and tracking of services Its architectural features that greatly influence the implementation of the system include (ibid p.108: a. Consolidation of services or the ability to merging other services to conform with SOA interfaces b. Loose coupling that minimize dependencies among different services c. Contract that define communication methods and procedures between services d. Abstraction or the process of prioritizing important aspects of a unit (Connolly & Beeg, 2005, p. 738) that allow services to hide their internal logic e. Reusability that allows division of functions into reusable services f. Ability to create a composite service through coordination of various services g. Ability to make service descriptions available and easy to discover 3.2 Relationship between SOA and Web Services SOA is an approach to distributed computing that exists long before Web services were introduced. Its main function is to separate business functionality into services with specific task. For instance, SOA may separate business functionality into services that include retrieval of personal information about an employee, data access authentication and validation, and presentation of required employee data (Greer, 2006, p.55). SOA and Web services are different but since SOA can be implemented using any technology, the latter can enable a true SOA by providing access over the Internet (Mittal & Kanchanavally, 2005, p.19) and letting new breed of SOA to perform Internet-based communication and drive interactions with more complex automated business processes (Cummins, 2008, p.13). When SOA is created using Web service, different technologies from various vendors can interoperate, as SOA is not dependent on any technology. Similarly, since Web Service is also independent and possess self-describing ability, it can offer a flexible environment for SOA (Gao, 2006, p.12). Web services and SOA are actually built out loose coupling principle that make swapping of components easy. Moreover, SOA provides Web services with mechanism for remote discovery of interfaces that enable applications to discover specific interface requirements dynamically. SOAP or Simple Object Access Protocol, WSDL, and UDDI are three important technologies providing Web services with key aspects of SOA. For instance, definition of a service and its interface specification are provided by WSDL, UDDI offer searchable directory while SOAP provides the mechanism for invoking the service as shown below (Vandersluis, 2004 p.70). Figure 3 - Web service architecture demonstrating the key aspects of SOA 4. Key features of different popular web architecture – SOAP, WSDL, REST, and other architecture that can be use to deliver internet applications. 4.1 SOAP Like many other successful web architecture, SOAP key features are simplicity and flexibility. These include the ability to define unit of communication and clearly identifiable messages, mechanism for error handling, and flexible method for data representation. Moreover, it also contains conventions for representing RPCs or Remote Procedure Calls as SOAP messages and a protocol-binding framework that enable sending and receiving SOAP messages across HTTP connections (Graham et al, 2004, p.20). 4.2 WSDL WSDL is an XML document that is divided into three main sections- the interface or portType element, binding element, and port element or the location of specific information. Therefore, Web services description need not reside on a single file since WSDL is capable of importing other documents residing on a different layer (Brown et al, p.814). This layering ability is the key feature of WSDL as it allows modification of rule in its ‘binding element’ to support different protocols like SOAP, HTTP_GET_POST, and others (Cohen et al, 2002, p.449). WSDL is an important feature within SOA and as a XML-based language it can describe the technical specifications of a Web service, operation offered by a Web service, the syntax required for the documents, the communication protocol required by the service, and the location of the service (Tari et al, 2011, p.18). 4.3 REST REST or Representational State Transfer is generally a mechanism where a service can pass a request query and receive an XML document in return. Like SOAP, REST is similar to DCOM as it can also transparently execute function calls between computer systems over a network. It is also platform and operating system independent. However, REST is simpler compared to other web services since it does not need abstractions and XML messages payloads while processing request through HTTP. Aside from its simplicity, REST is more secure as it can process read only request and can be password protected and encrypted with HTTPS (Caperhart & Caperhart 2007, p.363). 4.4 SEMANTIC WEB TECHNOLOGY 4.4.1 DAML-S DAML-S or DARPA Agent Markup Language where “S” stands for services is seen as an alternative service description mechanism. DAML-S is not different from WSDL in terms of concept but it is more complex particularly in syntax. This alternative web structure is based on the Resource Description Framework or RDF standard that has the ability to extend service description beyond traditional such as inclusion of semantic and functional information involving security, quality of service and so on (Snell et al, 2002, p.163). In fact, SWS or Semantic Web Service enables the development of secure communication across the network before sharing any information (Kumar et al, 2010, p.923) 4.4.2 WS-Inspection In terms of discovery, WS-Inspection or Web Service Inspection Language is considered one of few alternatives to UDDI as it can provide XML index for discovering Web services in a particular network (ibid p.176). However, unlike UDDI, it can inquire on a particular server directly and find out the services being offered rather acting as intermediary for locating services. Its initial design include ADS or Advertising and Discovery Services and DISCO and one the five Web service specifications put forth by Microsoft in 2001 along with WS-License, WS-Referral, WS-Routing, and WS-Security (Ferrara & MacDonald, 2002, p.330). 5. Comparison of two platforms for developing web services JAXP is a Java API XML Parsing package that includes a number of existing XML technologies such as the SAX engine, and event-based parser and extensible API using external plug-in modules. It supports DOM or Document Object Model and XSLT or Extensible Stylesheet Language Transformation where it enables programmers to convert XML content to other format such as HTML (Guruge 2004, p.251). However, although it allows dynamic programs to interact and work independently of HTML (Flannagan 1997, p.5), this Java platform package has limited support to SOAP as it only provide one API so Java application can send XML documents using SOAP when the need arises. In contrast, Web service development platforms such as .NET Framework and ASP.NET has strong support for SOAP-based Web services (Connoly, 2007, p.907; Naramore et al, 2005, p.7). In fact, Web services developed from .NET commonly support WSDL and SOAP (B’Far, 2005, p.70) and used by about 25% of all the Internet web sites (Doung & Rizzo, 2011, p.481). JAXP was developed under the J2EE framework, which is actually a set of open standards while .NET framework is a product suite from Microsoft. The latter provides not only provides runtime support for SOAP, WSDL, and UDDI but consider them as native .NET protocols. It can also build XML-based Web services by using a single platform ASP.NET whereas J2EE requires several APIs such JAXM, JAXP, JAXR, and JAX-RPC. Moreover, NET support BPM or business process management and e-Commerce in BizTalk server which are not directly provided by J2EE. 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