Web services have become a significant technology in the evolution of the Web and distributed computing. Web services represent a set of related standards that allow any two applications to communicate and exchange data via the Internet. The main components of these standards are the general architecture, the delivery protocol (SOAP), the description language (WSDL), and the discovery directory (UDDI).
Key Terms in this Chapter
Java WSDP: Java WSDP contains libraries for generating XML and SOAP, processing XML, accessing service registries, and calling RPC-based Web services. Java WSDP provides Java developers with a one-stop API solution for the development of Java Web service applications.
Java XML Pack: An architectural solution toolkit that is intended to ease software development by providing a set of high level APIs and reference implementations that abstract the complexities behind XML processing.
UDDP: UDDI enables developers and businesses to publish and locate Web services on a network. UDDI is originally designed by Microsoft, IBM, and Ariba, but has acquired significant industry backing. UDDI version 2.0 was released in June 2001 while UDDI 3.0.1, the latest version, was released in October 2003.
OWL-S/DAML-S: Both a communication language and ontology for describing Web services. OWL-S supplies Web service providers with a core set of markup language constructs for describing the properties and capabilities of their Web services in unambiguous, computer-interpretable form.
Ontology: An ontology can be defined as “an explicit formal specification of how to represent the objects, concepts, and other entities that are assumed to exist in some area of interest and the relationships that hold among them.” (Dictionary.com, 2003). Basically, this means that an ontology is a collection of domain concepts and their relationships.
Java WSDP Registry Server: An implementation of the UDDI version 3.0. The Java WSDP Registry Server serves the purpose of testing applications written using Java API for XML Registries (JAXR).
SOAP: SOAP is one of the common standards used to deliver Web services. Initially developed by DevelopMentor, Userland Software, and Microsoft, SOAP was conceptualized in 1998 and published as SOAP 0.9 in 1999. After several versions released from above companies, the protocol was submitted to the W3C.
OGSA: The open grid services architecture is a set of core capabilities and behaviors that address key concerns in grid systems. OGSA uses most of Web service technologies, notably WSDL and SOAP, but it aims to be largely agnostic in relation to the transportlevel handling of data upon the grid.
Agent-Based System: An agent-based system is a system in which the key abstraction used is that of an agent. Agent-based system enjoys the following properties: autonomy, reactivity, pro-activeness, and sociability.
Grid: Grids provide an infrastructure for federated resource sharing across trust domains. Much like the Internet on which they build, current Grids define protocols and middleware that can mediate access provided by this layer to discover, aggregate, and harness resources.
WSDL: The WSDL specification emerged when Microsoft and IBM decided to combine their description technologies into a universal standard. In March 2001, Microsoft, IBM, and Ariba submitted WSDL 1.1 to the W3C. Currently the W3C is working on a version 2.0 of the language.