Web Services Resource Framework
The Web Services Resource Framework ( WSRF ) is one of the Organization for the Advancement of Structured Information Standards ( OASIS ) software released collection of modular detailed specifications and describes how using Web services (software applications) queried stateful resources, modified, and can be represented. The specifications of WSRF include various patterns ( Patterns ) for definition, operations, error handling, and life cycles of resources.
Development and basis
Organizations and consortia like 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.
Basic objective of the WSRF was to define communication between different Web Services that access to resources, and to ensure reusability of resources. The WSRF is an evolution of OGSI. In the wake of this syntax and terminology were changed to create a better, more logical division of specifications. Likewise, the internal standards were added to the WS - Notification and Addressing specification. By the mentioned developed standards compatibility, sharing, portability and expansion of the grid systems is facilitated.
Among many other standards WSRF provides a foundation to build on the offered Web / Grid Services. Since the Web services are inherently stateless, simulating stateful services has been implemented as well. This occurs due to the use of a token that (request) is sent along with the SOAP message for each request.
In WSRF using the token remains hidden or transparent for each client. The token is also known as Endpoint Reference ( EPR). When creating a resource of the EPR is sent to the client in response, which is embedded in every method call in the SOAP message. The transparency is created with help from WS Addressing ( part WSRF standard).
WSRF specifications
Compared to OGSA WSRF provides better clarity and a more logical division according to subject. The WSRF specifications includes the following individual:
WS- Resource Property
This partial specification describes operations that allow access to the ResourceProperties. It offers the possibility of one or more properties of a resource to modify or query also state values of resources. Get-, Set - DeleteResourceProperty methods or individual properties can be returned, are set or cleared.
Similarly, all properties of a resource in a Resource Property Document ( RPD ) must be saved.
WS- Resource Lifetime
The WS- Resource Lifetime specification part is used to set the lifetime of the WS- Resource, retrieve, or control the life cycle of the generated instances. A distinction is made between timed and immediate destruction. The time of destruction shall not arbitrarily far in the future. After a client has requested a resource, it will be released after a certain time for the other clients. The immediate destruction is initiated by the client, the time-controlled by the server.
If required by the client, the life must be extended easily. After the execution of each action, whether successful or unsuccessful, a message to the client is always transmitted.
WS- Service Group
Sometimes it makes sense, due to the common properties to group multiple resources. This standard summarizes for this purpose together various operations. With the help of the so-called MembershipContentRules the laws or criteria are established which affect the membership of the corresponding group. The aim of the group is application- dependent, essentially. Thus, one can not only define the memberships, but also to administer.
The administrative and registration functions are in turn taken over by a Service Group Registration. A web service can include multiple service groups. The access to the group is performed by reference. Each entry includes an unambiguous reference to the resource and other potential metadata about the entry.
WS- BaseFaults
In an SOA environment is very important to define a predefined format for the error- descriptive messages. This specification includes all error messages based on XML schema. All WS messages have a similar structure, since they are all derived from the BaseFaultType. That's why they include the same information, such as error description, timestamp, error code, or source of the error.
By using a standardized format error, the management of faults, detection of problems encountered is facilitated.
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 its applications. It contains WS components such as Java and C implementations.
The Grid computing is structured heterogeneous. Meanwhile, globally distributed resources are summarized by grid and communicate via Wide Area Network (WAN). The services that have been developed for Grid computing, are nothing more than classic web services with multiple requirements. To meet all these requirements and to standardize standards have been developed, such as, among others, the WSRF.