There are essentially two interfaces to the Index Service -- one for getting information into the index, and one for retrieving information from the index.

Information is retrieved from the Index Service as service group entries using the standard WS MDS Core APIs for resource property queries or subscription/notification.

Because the Index is implemented as a WS MDS Aggregator Framework, the programmatic interface for getting information into the index is to create an aggregator source. The Aggregator Framework's architecture is described in the next section.

1. Aggregator Framework architecture

The MDS4 Aggregator Framework is the software framework on which MDS4 aggregator services are built. The Aggregator Framework collects data from an aggregator source and sends that data to an aggregator sink for processing.

Aggregator sources distributed with the Globus Toolkit include modules that query resource properties, acquire data through subscription/notification, and execute programs to generate data.

Another way of describing the Aggregator Framework is that it is designed to facilitate the collecting of information from or about WS-Resources via plugin aggregator sources and the feeding of that information to plugin aggregator sinks, which can then perform actions such as re-publishing, logging, or archiving the information.

Figure 1. Graphic of Information Services Flow

Aggregators work on a type of service group called an AggregatorServiceGroupRP. Resources may be registered to an AggregatorServiceGroupRP using the service group add operation, which will cause an entry to be added to the service group. The entry will include configuration parameters for the aggregator source; when the registration is made, the appropriate aggregation source and sinks will be informed; the aggregator source will begin collecting data and inserting it into the corresponding service group entry, and the aggregator sink will begin processing the information in the service group entries.

The method of collection by source and processing by the sink is dependent on the particular instantiation of the aggregator framework.

1.1. Standard aggregator sinks

The aggregator sinks distributed with the toolkit (org.globus.mds.aggregator.impl.ServiceGroupEntryAggregatorSink and org.globus.mds.trigger.impl.TriggerResource) are described in the following table.

Table 1. Standard aggregator sinks

Aggregator Sink	Service Implemented	Description
`ServiceGroupEntryAggregatorSink`	Index Service	The servicegroup sink (used by the Index Service) publishes received data as content in the AggregatingServiceGroup entry used to manage the registration. This data can therefore be retrieved by querying the index for its 'entries' resource property.
`TriggerResource`	Trigger Service	The Trigger Service provides an aggregator sink which receives data, applies tests to that data, and if the tests match, runs a specified executable. See the Trigger Service documentation for more information.

1.2. Standard aggregator sources

The aggregator sources supplied with the toolkit collect information using resource property queries (query sources), subscription/notification (subscription sources), and execution of external programs (execution sources).

The aggregator sources supplied with the Globus Toolkit are listed in the following table.

	Note
	All aggregator sources listed in this table are in the `org.globus.mds.aggregator.impl` package, so for example the aggregator source listed as `QueryAggregatorSource` is actually `org.globus.mds.aggregator.impl.QueryAggregatorSource`

Table 2. Standard aggregator sources

Aggregator Source Description

QueryAggregatorSource

Aggregator Source	Description
QueryAggregatorSource	The query source collects information from a registered resource by using WS-Resource Properties polling mechanisms: `GetResourcePropertyPollType`; requests a single Resource Property from the remote resource. `GetMultipleResourcePropertiesPollType`; requests multiple Resource Properties from the remote resource. `QueryResourcePropertiesPollType`; requests a query be executed against the Resource Property Set of the remote resource. Polls are made periodically, with both the period and target Resource Properties specified in the registration message.
SubscriptionAggregatorSource	The subscription source collects information from a registered resource using WS-Notification mechanisms. Data is delivered when property values change, rather than periodically.
ExecutionAggregatorSource	The execution source collects information about (not necessarily from) a registered resource by execution of a local executable, which is passed as input the identity of the registered resource. Details of the interface between the execution source and local executables are in Configuring Execution Aggregator Source.

The query source collects information from a registered resource by using WS-Resource Properties polling mechanisms:

GetResourcePropertyPollType; requests a single Resource Property from the remote resource.
GetMultipleResourcePropertiesPollType; requests multiple Resource Properties from the remote resource.
QueryResourcePropertiesPollType; requests a query be executed against the Resource Property Set of the remote resource.

Polls are made periodically, with both the period and target Resource Properties specified in the registration message.

SubscriptionAggregatorSource The subscription source collects information from a registered resource using WS-Notification mechanisms. Data is delivered when property values change, rather than periodically.

ExecutionAggregatorSource The execution source collects information about (not necessarily from) a registered resource by execution of a local executable, which is passed as input the identity of the registered resource. Details of the interface between the execution source and local executables are in Configuring Execution Aggregator Source.

Prev		Next
Tutorials	Home	APIs