OGC PUB/SUB Aka OGC Publish/Subscribe Interface Standard 1.0

Transcription

1 OGC PUB/SUB Aka OGC Publish/Subscribe Interface Standard 1.0 Lorenzo Bigagli National Research Council of Italy Institute of Atmospheric Pollution Research (CNR-IIA), Italy Event-based Dissemination and Processing of Geospatial Information Wageningen (NL), 9 May 2017

2 Outline Background and introduction PubSub 1.0 Use-cases, design, etc. Application: OGC Testbed 12 Conclusions

3 Typical OWS MEP: request/reply GetCapabilities( ) Service Capabilities, Dataset Identifiers, etc. DescribeDataset( identifier ) Dataset Descriptions OGC Service Client GetDataset( identifier, filter ) Filtered Dataset OGC Service (WFS, WCS, SOS, etc.) May be impractical for processes with long runtime, e.g. Model Web, distributed discovery May be insufficient when depending on specific events, e.g. external communications, status changes, natural phenomena, data updates Polling is the usual workaround, but not a solution 2

4 Publish/Subscribe model Subscribe( identifier, filter ) notify( datasetdescriptor or data ) OGC Service Client notify( datasetdescriptor or data ) notify( datasetdescriptor or data ) Notification Service Ability to specify an ongoing (persistent) expression of interest Asynchronous delivery Stateful behaviour Complementary to request/reply Request initial state, then subscribe to updates Can result in less (or more predictable) network traffic Supports reacting to urgent but unpredictable data, e.g. events, hazard warnings, sensor failures

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6 Background

7 PubSub (SWG) use-cases Service Filtered Data Push Service Filtered Notification Notification of Threshold Crossings Handling Multiple Event Types and Data Models GeoSynchronization (GSS) Brokered publish/subscribe Data Distribution FAA SAA Dissemination Pilot Emergency/Safety Critical Application Communication Protocol - Open GeoSMS Distributed Data Synchronization Message Aggregation Message Filtering / Batching Messages

8 PubSub (SWG) rationale Provide notification capabilities as a module to existing services No impact on existing service semantics Reuse service-specific filtering semantics Support pushing actual data from OGC Web Services, i.e. WCS, WFS, SOS Support pushing notifications about new data E.g. service and dataset updates, in order to optimize harvesting by catalogs

9 PubSub Core (PSC) Abstract description of the mandatory PubSub functionality Independent of the underlying binding technology Extensions defines several optional capabilities n E.g. batching, heartbeat

10 Basic PubSub interaction

11 PSC Conformance Classes

12 PSC Interfaces

13 Main design elements Pluggable filter language E.g. OGC Filter Encoding Publication metadata Pluggable delivery method E.g. ATOM, WS-Notification, AMQP

14 PubSub SOAP Binding (PSSB) How the PubSub functionality is realized in SOAP Based on OASIS WS- Notification Additional conformance class: Reliable Publisher n Based on WS- ReliableMessaging

15 PubSub Conformance Classes

16 OGC Testbed 12 Initiative Three approaches tested WPS fac ades Specific extensions to each OGC Web Service with asynchronous request/reply capabilities PubSub Standard n All successful, PubSub the most flexible CNR contribution PubSub-CSW [prototype demo client] Generic PubSub-OWS n Accepts OWS requests as filters n Delivers OWS replies as updates/data pushes

17 Example: PubSub-CSW MEP 1. Subscribe( filter = GetRecordsRequest#1 ) 2. GetRecordsRequest# GetRecordsResponse CSW Client 3. Notify( TransactionResponse ) 4. Notify( TransactionResponse ) CSW 1. CSW client subscribes with a specific getrecordsrequest 2. Time-0 recordset obtained via standard Request/Reply 3. Subsequent updates based on CSW Transaction semantics

18 Conclusions OGC PubSub 1.0 standard bridges a gap between the existing SDI standard baseline and the many technologies supporting server-initiated, asynchronous communications See also (pending OGC approval) Bigagli L (2016) OGC Testbed-12 PubSub / Catalog Engineering Report. Proß B (2016) OGC Testbed-12 Implementing Asynchronous Services Response Engineering Report Rieke M, Balaban A (2016) OGC Testbed-12 Asynchronous Messaging for Aviation Engineering Report Simonis I (2017) OGC Testbed-12 Results Engineering Report Upcoming Bigagli L, Rieke M. The new OGC Publish/Subscribe Standard - applications in the Sensor Web and the Aviation domain. Open Geospatial Data, Software and Standards, ISSN , Springer, in publishing

19 OGC PUB/SUB Aka OGC Publish/Subscribe Interface Standard 1.0 Lorenzo Bigagli National Research Council of Italy Institute of Atmospheric Pollution Research (CNR-IIA), Italy Event-based Dissemination and Processing of Geospatial Information Wageningen (NL), 9 May 2017