Linked Data Notifications for RDF Streams
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This document discusses using Linked Data Notifications (LDN) for RDF data streams. It proposes modeling RDF streams as identified Web resources with input and output endpoints. Streams can be discovered and their endpoints retrieved. Data can be sent to input endpoints and retrieved from output endpoints. Queries can be registered against streams to generate output streams. The approach uses existing standards like LDP and aims to provide a simple, generic protocol for decentralized communication between heterogeneous RDF stream processors and consumers.
![17
Sending stream notification
• POST stream elements
• body should contain the stream element that will be fed to the stream
POST /streams/my-stream/input HTTP/1.1
Host: example.org
Content-Type: application/ld+json
{
"prov:generatedAtTime": "2017-07-22T05:00:00.000Z",
"@id": "ex:Graph1",
"@graph": [
{ "@id": "ex:humidityObservation",
"ex:hasValue": 34.5}],
"@context": {
"prov": "http://www.w3.org/ns/prov#",
"ex": "http://example.org#"} }
RSP
ReceiverPOST
stream
inputRSP Sender](https://image.slidesharecdn.com/presentationiswc2017-171023115506/85/Linked-Data-Notifications-for-RDF-Streams-17-320.jpg)
![18
• GET stream elements from an RDF stream endpoint
• return the notification URIs listed as objects to the LDP
ldp:contains predicate.
• stream elements "fade" with time
• listed stream contents may progressively change.
{
"@context": "http://www.w3.org/ns/ldp",
"@id": "http://example.org/streams/my-stream/output",
"contains": [
"http://example.org/streams/my-stream/output/graph1",
"http://example.org/streams/my-stream/output/graph2" ]
}
Publicizing stream elements
RSP
ReceiverPOST GET
stream
input
stream
outputRSP Sender RSP Consumer](https://image.slidesharecdn.com/presentationiswc2017-171023115506/85/Linked-Data-Notifications-for-RDF-Streams-18-320.jpg)
![19
Pulling stream elements
• Consumer explicitly requests for stream sub-sequences
• Practical to limit through size, time, filter parameters
{
"@context": {
"prov": "http://www.w3.org/ns/prov#",
"ex": "http://example.org#"},
"@graph": [
{ "prov:generatedAtTime": "2017-07-22T05:00:00.000Z",
"@id": "ex:Graph1",
"@graph": [
{ "@id": "ex:humidityObservation","ex:hasValue": 34.5 }]
},
{ "prov:generatedAtTime": "2017-07-22T06:00:00.000Z",
"@id": "ex:Graph2",
"@graph": [
{ "@id": "ex:humidityObservation","ex:hasValue": 44.5 }]
}
]
}](https://image.slidesharecdn.com/presentationiswc2017-171023115506/85/Linked-Data-Notifications-for-RDF-Streams-19-320.jpg)
![21
Register a query
• An actor may POST a query to an RSP endpoint
• Query must reference a valid registered RDF stream.
• RSP endpoint should return the URI of the resulting output stream, so that its
results can be retrieved (pulling or pushing).
RDF stream:
http://example.org/streams/my-stream
Query:
SELECT ?s ?p ?o
WHERE {
STREAM <http://example.org/streams/my-stream> [RANGE 2s]
{?s ?p ?o}
}](https://image.slidesharecdn.com/presentationiswc2017-171023115506/85/Linked-Data-Notifications-for-RDF-Streams-21-320.jpg)
Linked Data Notifications for RDF Streams
- 1. Linked Data Notifications for RDF Streams Jean-Paul Calbimonte Institute of Information Systems University of Applied Sciences and Arts Western Switzerland (HES-SO Valais-Wallis) International Semantic Web Conference ISWC Vienna, October 2017 @jpcik
- 2. 2 HES-SO: University of Applied Sciences and Arts Western Switzerland We are here, surrounded by mountains!
- 3. 3 Linked Data Notifications for RDF Streams 1
- 4. 4 RDF Streams triplesRDF graph: graph Triple Store store post query triples graph+ timestampRDF stream graph: (graph, t) feed register query triplesRDF Stream Processor
- 5. 5 RSP Data Model https://github.com/streamreasoning/RSP-QL/blob/master/Semantics.md Timestamped Graph :g1 {:axel :isIn :RedRoom. :darko :isIn :RedRoom} {:g1 prov:generatedAtTime "2001-10-26T21:32:52"} Many/One-triple graphs Multiple time predicates Implicit timestamp Different timestamp representations Contemporaneity Allows: A RDF stream S consists of a sequence of timestamped graphs (with a partial order) RDF Stream :g1 {:axel :isIn :RedRoom. :darko :isIn :RedRoom} {:g1,prov:generatedAtTime,t1} :g2 {:axel :isIn :BlueRoom. } {:g2,prov:generatedAtTime,t2} :g3 {:minh :isIn :RedRoom. } {:g3,prov:generatedAtTime,t3} ... https://www.w3.org/community/rsp/ http://w3id.org/rsp/abstract-syntax
- 6. 6 RDF Stream Processors Triple Wave CSPARQL Etalis TrOWL CQELS Morph streams RDF stream RDF stream RDF stream RDF stream RDF stream
- 7. 7 Linked Data Notifications for RDF Streams 2
- 8. 8
- 9. 9 LDN: Basics Sender Target Receiver Consumer Resource which notifications is to/about sends notifications consumes notifications exposes notifications through inbox creates notifications in inbox inbox
- 10. 10 LDN: Discovery Sender Consumer Target GET/HEAD GET/HEAD inbox inbox
- 11. 11 LDN Interactions Sender Consumer ReceiverPOST GET notifications Inbox Consumer Receiver GET ldp:contains Inbox notifications
- 12. 12 LDN for RDF Streams 3
- 13. 13 We think LDN can help to get here: Triple Wave CSPARQL Etalis TrOWL CQELS Morph streams RDF stream RDF stream RDF stream RDF stream RDF stream
- 14. 14 Streams and IRIs • An RDF stream is uniquely identified by an IRI • Stream IRI: obtain information about the stream • endpoints • RDF stream is a read/write Web resource detached from potentially multiple endpoints used to interact with its contents.
- 15. 15 Endpoint discovery The endpoints of an RDF stream: GET http://example.org/streams/my-stream Response should include metadata about the stream: { "@context": "http://www.w3.org/ns/ldp", "@id": "http://example.org/streams/my-stream", "inbox": "http://example.org/streams/my-stream/inbox" } RSP Sender RSP Consumer RDF StreamGET/HEAD GET/HEAD inbox inbox
- 16. 16 Input/output stream • Specialize it in two distinct types: an input inbox and an output inbox. • Input stream: receiving notifications (i.e. to be fed) by senders. • Output stream: only meant to be consumed, as they are produced by an RSP engine. { "@context": "http://w3id.org/rsp/ldn-s", "@id": "http://example.org/streams/my-stream", "input": "http://example.org/streams/my-stream/input" }
- 17. 17 Sending stream notification • POST stream elements • body should contain the stream element that will be fed to the stream POST /streams/my-stream/input HTTP/1.1 Host: example.org Content-Type: application/ld+json { "prov:generatedAtTime": "2017-07-22T05:00:00.000Z", "@id": "ex:Graph1", "@graph": [ { "@id": "ex:humidityObservation", "ex:hasValue": 34.5}], "@context": { "prov": "http://www.w3.org/ns/prov#", "ex": "http://example.org#"} } RSP ReceiverPOST stream inputRSP Sender
- 18. 18 • GET stream elements from an RDF stream endpoint • return the notification URIs listed as objects to the LDP ldp:contains predicate. • stream elements "fade" with time • listed stream contents may progressively change. { "@context": "http://www.w3.org/ns/ldp", "@id": "http://example.org/streams/my-stream/output", "contains": [ "http://example.org/streams/my-stream/output/graph1", "http://example.org/streams/my-stream/output/graph2" ] } Publicizing stream elements RSP ReceiverPOST GET stream input stream outputRSP Sender RSP Consumer
- 19. 19 Pulling stream elements • Consumer explicitly requests for stream sub-sequences • Practical to limit through size, time, filter parameters { "@context": { "prov": "http://www.w3.org/ns/prov#", "ex": "http://example.org#"}, "@graph": [ { "prov:generatedAtTime": "2017-07-22T05:00:00.000Z", "@id": "ex:Graph1", "@graph": [ { "@id": "ex:humidityObservation","ex:hasValue": 34.5 }] }, { "prov:generatedAtTime": "2017-07-22T06:00:00.000Z", "@id": "ex:Graph2", "@graph": [ { "@id": "ex:humidityObservation","ex:hasValue": 44.5 }] } ] }
- 20. 20 Pushing stream elements Proactively send stream elements to the consumer Example: Server-Sent Events protocol (HTTP-based). • Continuously push RDF stream elements, • One-directional (vs. bidirectional in WebSocket) • Each data item is prefixed by the data: annotation. Provide additional push protocols (different endpoints) diverges from LDN can only advertise one inbox
- 21. 21 Register a query • An actor may POST a query to an RSP endpoint • Query must reference a valid registered RDF stream. • RSP endpoint should return the URI of the resulting output stream, so that its results can be retrieved (pulling or pushing). RDF stream: http://example.org/streams/my-stream Query: SELECT ?s ?p ?o WHERE { STREAM <http://example.org/streams/my-stream> [RANGE 2s] {?s ?p ?o} }
- 22. 22 LDN for RDF streams • Simple, generic, extensible protocol • Encapsulate behavior or heterogeneous implementations • Use of existing Standards/recommendations • Decentralized communication • Potential for interoperability
- 24. gracias! ¿tienes preguntas? Jean-Paul Calbimonte University of Applied Sciences and Arts Western Switzerland HES-SO Valais-Wallis @jpcik