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Web Services and OGSA Tal Lavian, Phil Wang

Web Services and OGSA Tal Lavian, Phil Wang. What Are Web Services?. Conventions for program-to-program Communication Built on existing Web infrastructure - Usually HTTP carrying XML messages

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Web Services and OGSA Tal Lavian, Phil Wang

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  1. Web Services and OGSATal Lavian, Phil Wang

  2. What Are Web Services? • Conventions for program-to-program Communication • Built on existing Web infrastructure - Usually HTTP carrying XML messages • Adds WSDL (service descriptions), UDDI (service directory), and SOAP (XML-based RPC), plus a variety of XML encodings of data

  3. Characteristics of Web Services • Easy to implement on web servers – development tools hide most of the messy details • Message-oriented client-server protocol, stateless between messages (except for state kept by the client or server application) • No standards for service behavior – services can do anything any way they want

  4. OGSA/OGSI and Web Services • OGSA builds on Web Services – OGSA services are Web Services • OGSA model isn't a perfect fit for the Web Services model • OGSA adds constraints and facilities specific to Grid requirements

  5. OGSA Model • Job scheduling model vs. Web Services' atomic transaction model • Jobs run anywhere their resource requirements can be met vs. Web Services' stationary service model • Complex cross-organizational and resource issues are not addressed in Web Services

  6. OGSA Extensions to Web Services • Service life cycles – service instances can be created and destroyed by clients – mainly used for job scheduling • Certain standard interfaces for services, including a publish/ subscribe/notify interface • State data for services, accessible to clients via a standard interface – but falls short of a database interface

  7. OGSA Extensions, continued • Service registration and discovery – analogous to UDDI but with service instance data as well • Single sign-on security model using SSL and a proxy certificate concept • Use of job schedulers / resource brokers to manage services

  8. OGSA Extensions, continued • Standard logging facility regardless of platform (based on the Jakarta commons logging API) • Standard error message format

  9. What About Optical Network Allocation? • Should conform to OGSA where there's no good reason not to, for example security, logging, and error message conventions. • Resource discovery interface to brokers and schedulers will need to be designed for best interoperation. • Current resource brokers don't deal with network resources, so there is a large gap to be filled

  10. Optical Network Allocation, continued • The notification interface would be useful for asynchronous callbacks. • Network allocation fits the web service model pretty well, so some OGSA extensions are irrelevant. • Transient services and service state data are not especially relevant

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