WS-Resource Framework
The Web Services Resource Framework (WSRF) is a software collection of modular individual specifications published by the Organization for the Advancement of Structured Information Standards (OASIS) and describes how state-related resources can be queried, changed and represented with the help of web services . The WSRF specifications include various patterns for definition, operations, error handling, and resource life cycles.
Development and Basis
Organizations and consortia such as OASIS deal with the development of grid standards such as Open Grid Services Architecture (OGSA), Open Grid Services Infrastructure (OGSI), Web Services Resource Framework (WSRF), Universal Description, Discovery and Integration (UDDI) etc.
The basic aim of the WSRF was to define communication between different web services that access resources and to ensure that resources can be reused. The WSRF is a further development of the OGSI. In the course of this evolution, syntax and terminology have been changed to create a better, more logical division of specifications. The internal standards have also been expanded to include the WS notification and addressing specification . The listed, developed standards facilitate the compatibility, sharing, portability and expansion of grid systems.
In addition to many other standards, WSRF forms a basis on which the offered web / grid services are built. Since the web services are inherently stateless, the simulation of stateful services has also been implemented. As a result, a token is used , which is sent with the SOAP message with every request .
The use of the token remains hidden or transparent for each client in the WSRF. The token is also known as the Endpoint Reference (EPR). When a resource is created, the EPR is sent to the client as a response, which is embedded in the SOAP message for each method call. The transparency is created with the help of WS Addressing (WSRF partial standard).
WSRF specifications
Compared to OGSA, WSRF offers a better overview and a more logical division into subject areas. The WSRF contains the following individual specifications:
WS-ResourceProperty
This sub-specification describes operations that allow access to the ResourceProperties . It offers the possibility to change individual or several properties of a resource or to query the status values of resources. With Get, Set or DeleteResourceProperty methods , individual properties can be returned, set or deleted.
All properties of a resource must also be saved in a Resource Property Document (RPD) .
WS-ResourceLifetime
The WS-ResourceLifetime partial specification is used to set the lifespan of the WS-Resource, to call it up, or to control the lifecycle of created instances. A distinction is made between time-controlled and immediate destruction. The point in time of destruction can be as far in the future as you like. After a client has requested a resource, it is released for the other clients after a certain period of time. The immediate destruction is triggered by the client, the time-controlled destruction by the server .
If necessary, the client simply has to extend the service life. A message is always sent to the client after each action has been carried out, whether successful or unsuccessful.
WS-ServiceGroup
Sometimes it makes sense to group several resources because of their common properties. This standard combines various operations for this purpose. With the help of the so-called MembershipContentRules , the laws or criteria are defined which influence membership in the corresponding group. The goal of the grouping is essentially application-dependent. Thus you can not only define the affiliations, but also administrate them.
The administration and registration functions are in turn taken over by a Service Group Registration . A web service can belong to several service groups. The groups are accessed through references. Each entry contains a clear reference to the resource and other possible metadata about the entry.
WS-BaseFaults
In a SOA environment it is very important to define a predefined format for the error-describing messages. This specification includes all error messages based on XML schema . All WS messages have a similar structure as they are all derived from the BaseFaultType . Therefore, they contain the same information, for example error description, time stamp, error code or source of the error.
A standardized error format facilitates the management of errors and the detection of problems that have occurred.
Implementation examples
The Globus Toolkit 4 (GT4) is a mediation layer between the application and the system layer. GT4 is a technology for creating grids on which a user can run his applications. It contains WS components such as Java and C implementations.
Grid computing is structured heterogeneously. Its resources, which are distributed around the world, are grouped together by a grid and communicate with one another via a wide area network (WAN). The services that were developed for grid computing are nothing more than classic web services with multiple requirements. In order to meet and standardize all of these requirements, standards such as the WSRF have been developed.
See also
Individual evidence
- ↑ docs.oasis-open.org (PDF, 116 KB) - accessed on March 9, 2013
- ↑ www.w3.org - Web Services Addressing English - accessed on March 9, 2013
- ↑ Web Services Resource Framework (WSRF) (PDF, 528 KB) - accessed March 9, 2013