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Data Mgt
MDS4
Execution Mgt
Although the basic functionality remains the same for MDS in GT4, the architecture has changed from OGSI in GT3 to WSRF in GT4. In OGSI, services advertise service data; in WSRF, services advertise resource properties. Resource Properties and service data are very similar -- both provide a mechanism for expressing arbitrary data about grid resources in XML format, as well as query and notification/subscription interfaces to that data.
The GT4 Index Service provides the same functionality as the GT3 Index Service; however, the GT4 Index Service supports WSRF service group registration and resource property query and subscription/notification mechanisms, while the GT3 Index Service supported OGSI service group registration and service data query and subscription/notification mechanisms.
The following table shows a mapping of some GT3 concepts/tools to GT4.
Table 1. Comparison of MDS in GT3 and GT4
| Description | GT2 Version | GT4 Version |
|---|---|---|
| Query Operations | FindServiceData (to retrieve a single service data element by name or to perform an XPath query against a service's service data elements) | GetResourceProperty (to retrieve a single resource property by name), GetMultipleResourceProperties (to retrieve multiple resource properties by name), and QueryResourceProperties (to perform an XPath query against a service's resource properties). |
| APIs used for queries | OGSI (GT3) Core APIs | WS Core APIs |
| Command-line clients used for queries | ogsi-find-service-data | wsrf-get-property, wsrf-get-properties,
wsrf-query |
| Available GUIs | globus-sdb (standalone client) and WebSDB (web interface) | WebMDS (web interface) |
| Operations for subscription/notification | OGSI NotificationSource / NotificationSink | WS-Notification |
| APIs used for subscription/notification | OGSI (GT3) Core APIs | WS Core APIs |
| Index registration mechanism | GT3 services can be configured to publish their service data to index services. | Index Servers maintain aggregating service groups that
include registration information (timeout values, the mechanism to
use to acquire information, and additional mechanism-specific parameters)
The registration is accomplished by
adding an entry to an aggregating service group via the
mds-servicegroup-add command. In addition, services
may be configured to register themselves to the default index server
running in the same container. |
A more detailed mapping of OGSI concepts to WSRF concepts can be found here.