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The figure shows that three different event types are in use at the service. The events are published in AIXM and WXXM encodings more specifically, as dnotam:Event and
wx:Forecast wx:Observation on two event channels. Each channel has been assigned a specific name which uniquely identifies the channel semantics for a given domain.
Note: the XML implementation of the event metadata shown in Figure 30 can be found in Annex D – Event
Metadata XML Implementation , section 16.2.
Figure 31: Example of Event Metadata for SFE Service – UML Object Diagram
Notation
Figure 31 shows that two different event types are in use at the service. The events are published in OM and CAP encodings on two event channels. Each channel has been
assigned a specific name which uniquely identifies the channel semantics for a given domain.
Note: the XML implementation of the event metadata shown in Figure 31 can be found in Annex D – Event
Metadata XML Implementation , section 16.3.
The example metadata described in above figures was used to test the event service discovery model, which is discussed in the following sections.
Copyright © 2010 Open Geospatial Consortium, Inc.
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7.3 The Event Service Discovery Model
The goal of the work described in this chapter is to be able to discover Event Services by querying event service metadata for both event channels and OGC Filter functionality.
Assumptions
1. The Event Services provide a method i.e. GetCapabilities from which one is
able to obtain their OGC Capabilities document. This document lists the Services Filter Capabilities.
2. The Event Services provide a method from which one is able to obtain the
TopicSet document which lists the Event Channels e.g. Topics, Event Types and relationships.
3. A taxonomy representing each type of OGC Filter Capability defined in the OGC
FE 2.0.0 is assumed to exist. Querying based on Filter Capabilities can be accomplished by classifying each Service
based on functionality declared in its Capabilities document and using the taxonomy that identifies the individual features to represent each function.
Querying based on a Services supported Event Channels is accomplished by representing each channel and event-type as an object and then linking them together in a hierarchical
manner.
Event Service ----- Event Channel [name=foo] ----- Event-Type [name=bar]
Figure 32 shows the model that is used for discovery. This model was created based upon the event metadata model described in section 6.2.1.3.
Note: Annex C – Additional Event Discovery Material - section 15.1 – contains the transaction request to
populate a registry with this model.
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Figure 32: Registry Model for Event Service Discovery
7.4 The Event Service Discovery extension package
The components required to support the Event Service Discovery model are listed in the following table.
Table 33: Event Service Discovery Model Components
Component Description of Component instances
Object Types EventChannel, EventType
Association Types HasChannel, ChannelBinding
Classification Node Sensor event service type, AIM event service type new C-
Nodes added to existing ServiceType scheme Classification Schemes Scheme for Filter 2.0.0 Operators and Operands
Note: The optional part of the model referring to a Schema object is not implemented in the current OWS project due to time constraints. It is documented in the model so it can be explored in a future OWS project.
