Abstract
The potential growth of applications distributed over a network and the large number of users has created the need for an infrastructure which can support increasing interaction among such users and applications. In this environment a scalable solution is needed. This problem known as application integration is addressed in this chapter, and it is combined with Semantic Web technology. After introducing the different techniques to overcome the application integration challenge current trends in Semantic Web Services are discussed and the most recent R&D projects and a selection of available tools are presented. Also discussed is the use of ESB as a suitable mechanism to deploy Semantic Web Services.
TopBackground
With the expansion of the local networks and the Internet in the 90s, a need arose for applications to communicate with each other. This communication consists in exchanging data and computational effort among different processes with the ultimate goal of building a distributed system. Several solutions have been proposed to overcome the problem of communicating different applications across a network and using this network within a global environment. This problem, known as application integration, has now become a priority task among system providers.
Key Terms in this Chapter
CORBA: The Common Object Request Broker Architecture (CORBA) is a standard defined by the Object Management Group (OMG) that enables software components written in multiple computer languages and running on multiple computers to work together.
UDDI: Universal Description, Discovery and Integration (UDDI) is a platform-independent, XML-based registry for businesses worldwide to list themselves on the Internet. UDDI is an open industry initiative, sponsored by OASIS, enabling businesses to publish service listings and discover each other and define how the services or software applications interact over the Internet.
GIOP: General Inter-ORB Protocol (GIOP) is the abstract protocol by which object request brokers (ORBs) communicate. Standards associated with the protocol are maintained by the Object Management Group (OMG).
RMI: Remote Method Invocation is the Java implementation for performing the object equivalent of remote procedure calls. The Java Remote Method Invocation system allows an object running in one Java virtual machine to invoke methods on an object running in another Java virtual machine. RMI provides for remote communication between programs written in the Java programming language.
SAWSDL: The Semantic Annotations for WSDL and XML Schema (SAWSDL) W3C Recommendation defines mechanisms using which semantic annotations can be added to WSDL components. SAWSDL does not specify a language for representing the semantic models, e.g. ontologies. Instead, it provides mechanisms by which concepts from the semantic models that are defined either within or outside the WSDL document can be referenced from within WSDL components as annotations.
RPC: Remote procedure call (RPC) is an inter-process communication technology that allows a computer program to communicate with a procedure running in another address space (commonly on another computer on a shared network) without the programmer explicitly coding the details for this remote interaction.
SOA: Service Oriented Architecture (SOA) is a software architecture where functionality is grouped around business processes and packaged as interoperable services. SOA also describes IT infrastructure which allows different applications to exchange data with one another as they participate in business processes. The aim is a loose coupling of services with operating systems, programming languages and other technologies which underly applications.
WSDL: The Web Services Description Language (WSDL) is an XML-based language that provides a model for describing
OMG: The Object Management Group, Inc. (OMG) is an international organization supported by over 600 members, including information system vendors, software developers and users. Founded in 1989, the OMG promotes the theory and practice of object-oriented technology in software development. Primary goals are the reusability, portability, and interoperability of object-based software in distributed, heterogeneous environments. OMG Task Forces develop enterprise integration standards for a wide range of technologies, and an even wider range of industries. OMG’s modeling standards enable powerful visual design, execution and maintenance of software and other processes. OMG’s middleware standards and profiles are based on the Common Object Request Broker Architecture (CORBA) and support a wide variety of industries.
SOAP: SOAP is a simple and lightweight XML-based mechanism for creating structured data packages that can exchanged between network applications. SOAP consists of four fundamental components: an envelope that defines a framework for describing message structure, a set of encoding rules for expressing instances of application-defined data types, a convention for representing remote procedure calls (RPC) and responses, and a set of rules for using SOAP with HTTP. SOAP can be used in combination with a variety of network protocols; such as HTTP, SMTP, FTP, RMI/IIOP, or a proprietary messaging protocol.
IIOP: Internet Inter-Orb Protocol (IIOP) is the implementation of GIOP for TCP/IP. It is a concrete realization of the abstract GIOP definitions.
ESB: Enterprise Service Bus (ESB) provides an abstraction layer on top of an implementation of an enterprise messaging system, which allows integration architects to exploit the value of messaging without writing code. Contrary to the more classical enterprise application integration (EAI) approach the foundation of an enterprise service bus is built of base functions broken up into their constituent parts, with distributed deployment where needed, working in harmony as necessary.
EAI: Enterprise application integration (EAI) is the process of linking applications within a single organization together in order to simplify and automate business processes to the greatest extent possible, while at the same time avoiding having to make sweeping changes to the existing applications or data structures.
ORB: An object request broker (ORB) is a middleware technology that manages communication and data exchange between objects. ORBs promote interoperability of distributed object systems because they enable users to build systems by piecing together objects- from different vendors- that communicate with each other via the ORB (Wade, 1994). The developers are only concerned with the object interface details. This form of information hiding enhances system maintainability since the object communication details are hidden from the developers and isolated in the ORB (Cobb, 1995).
DCOM: Distributed Component Object Model (DCOM) is a proprietary Microsoft technology for communication among software components distributed across networked computers. DCOM extends Microsoft’s COM and provides the communication substrate under Microsoft’s COM+ application server infrastructure.