ResearchTopicsinMachineHypermediaSystemDesign

IRTFThingtoThingResearchGroupMarch15,2016

ResearchGoals

• Investigatedesignpatternsforinteroperablehypertextdrivenmachineinterfaces

• InvestigateRESTfuldesignpatternsforsensingandactuation

• Whatistheroleofmodelingandontologyinsemanticinteroperability?

ResearchTopics

• ReferenceSystemArchitecture• ContentFormatDesign• RESTfulAsynchronousCommunication• RESTfulActuation• RESTProtocolAbstraction• ModelBasedHypertextAnnotation

ReferenceArchitecture

BaseSchema

ResourceModel

ClientApplication

ThingObjectModel

(DeferredInterface)

DomainSchema

Resources

HypermediaControls

Discovery

DomainModel

HypermediaClient

ResourceApplication

(PhysicalI/O)

NetworksServer

PublicResource

Tools

Client

ContentFormatDesign

• Whatshouldacontent-formatdescribe?• RepresentationFormats• CommonInteractionModel– Resourcemodele.g.CoREInterfaces– Datamodele.g.SenML– Howlinkswork,e.g.CoRELink-Format– Howformswork– Howrelationtypesareused– Somebaserelationtypes

ContentFormatDesign

Protocols

RepresentationFormats

Common InteractionModel

ApplicationMeta-Model

ApplicationDomainModel

HTTP,CoAP,RD,WebLinking

SenML,Link-Format,HTML

Resources,Links,Forms,Collections

LinkRelations,FormRelations

ResourceTypes,Ontology

hsmlcontenttype

describedByrelationtype

ResourceModel

Link ItemLink ItemLinkLink

Link (self)

(sub)

Link

Collection

Link ItemLinkLinkLink

Form

Link ItemSubResourceCollection

Collection

LinkLink

Collection

Link

RepresentationFormatExample{

"bn": "/light/onOff/currentState/","e": [

{"vb": false,"n": ""

}],"l": [

{"href": "","rel": ["self","item"],"rt": ["property", "currentstate"],"ct": ["application/senml+json"]

}]

}

ItemsmayberepresentedinSenML

LinksmayberepresentedinCoRElink-format

Forms

{"anchor": "/light3/brightness/","rel": "invokeAction", "type": "change","method": "post","href": "actuations","accept": "application/hsml+json",

}

To"invokeAction"oftype"change"onthe"/light3/brightness/"resource,performa"post"totheresourceat"/light3/brightness/actuations"usingthe"application/hsml+json"contentformat

LinkandFormRelations

• LinkRelations– "item"(anembeddediteminacollection)– "sub"(asubresourceiteminacollection)– "form"(aformiteminacollection)– "grp"(agroupinteractionlink)

• FormRelations– "addItem"(addanitemtoacollection)

RESTfulAsynchronousCommunication

• RESTinteractionisastatemachinebetweenclientandserver– requestandresponse

• AsynchronousCommunicationusingRESTisoneormorestatetransitionresponsesthattakeplaceafterarequestismade

• Twoclassesofinteraction:– Betweenresourcesandapplications– FromResourcetoResource

ResourcetoApplication

• CoAPObserveisaRESTfulasynchronouscommunicationmethod

• Clientapplicationmakesstatechangesbasedonserverresponses

• Serveristhenameandstateoriginoftheresource

ServerClient

OBSERVE

Responses

ResourcetoApplication

• PUTorPOSTcanbeusedfortheclienttoupdatethestateoftheserver

• Clientapplicationchangesstateonserverasynchronously• Serveristhenameandstateoriginoftheresource

ServerClient

PUT/POST

Responses

ResourcetoResource

• Aclientinstancemaybe"bound"toaresourceandperformstatetransferbetweenitandanotherresource

• Observebindingupdatesthestateofthelocallyboundresourcebasedonresponsesfromthe"boundTo"resource

• ServerBisthenameandstateoriginoftheresource

ServerBOBSBind

Observe

ResponsesServerA

ResourcetoResource

• Pushbindingobservesthestateofthelocallyboundresourceandupdatesthe"boundTo"resource

• Localbindingmayincorporateafilterandmaybeforms-capable

• ServerBisthenameandstateoriginoftheresource

ServerBPushBind

PUT/POST

ResponsesServerA(obs)

NotificationResource• Collectionresourcetocapturenotificationsfromabinding• BindingusesPOSTtocreateanewresourceinthecollectionforeach

notification• ClientApplicationcanobservethecollectionfornewnotificationsbeing

createdandreceiverepresentations• ServerAisthenameandstateorigin

POSTBindServerA

(obs)Notifications Client

OBSERVE

Responses

Promise+• Patternforapplicationscriptstohandlerecurringeventslikenotificationsfromresourceobservations

• ExtendsthePromisepatternwithanupdatehandlerforrecurringevents

res.observe().then(onResolve, onReject, onUpdate)(…do other stuff)

onUpdate(value){processStateUpdate(value)

HTTPObserve• UsingatechniquebasedonHTML5ServerSentEvents(SSE)

• Header"Transfer-Encoding:chunked"enablesopenTCPconnectiontobeusedforasynchronousmessages

• MessagescouldbeformattedasHTTPResponseandheaderlines,withcontent-typeandcontent-lengthcontrols

• Headeroptionse.g.Observe:0couldbeusedtocreateaCoAP-compatibleobserveforHTTP

RESTfulActuation

• WhatisRESTfulactuation?• Changeofstateonaresourcethathassomeeffectinthephysicalworld

• Manydifferentinterpretationsofthis:– Updateofaresourcedirectlychangesphysicalstate– Updateofaresourcecommunicatesintendedstate– Creationofaresourcethatdescribestheintendedstatetransition

– Updateofasetpointresourceofacontroller

UpdateStateResource

• Thereisalwayssomeuncertainty,e.g.thephysicalprocessmayfailorbedelayed

• Willthestatereturnedonasubsequentreadreflecttheintendedstateortheactualstate?

• IntendedstateistechnicallyRESTfulbutnotuseful

• ActualstateisusefulbutnotRESTful• Delayingtheresponseuntilintendedstateisobservedmightwork…

UpdateIntendedStateResource

• ThiswillbebothRESTfulandUseful• AllowsaRESTresponsetobegeneratedfortheintendedstateandapplicationcanthenmonitorobservedstate

• Thiscouldwork,butwhataboutwherewewanttoparameterizeexecutionwithtransitiontimes,etc?Howdoweknowiftheactionisgoingtosucceedorfail?

CreateaStateTransitionResource

• ThisisRESTfulanduseful,usingtheresourcecreatepatternwithaform,andreturningaresourcelocationthatcanbemonitoredforstatechanges

• Allowsasynchronousnotificationandpromisetobeusedtotrackprogress,success,failureofrunningactions,alsotomodifyorcancel

• Multipleactionsmaybequeued

Controllers

• Thermostatisanexampleofacontroller• Temperaturesettingisaset-pointthatisinputtoacontrolleralgorithmthatdecideswhethertooperateanactuatorbasedontherelationshipoftheset-pointtothemeasuredtemperature,andperhapsothervariables

• Thermostathasmeasurementtemperatureandset-pointtemperatureinputs,andanactuatorstateoutput.

RESTProtocolAbstraction

ApplicationLogic

CommonCRUDRequests

MQTT

CommonCRUDResponses

ResourceModel

Resources

ResourceModel

ThingObjectModel

HTTP CoAP

CommonServer

CommonClient

PluggableProtocols

ResourceLogic

WS

DictionaryMappingofCommonRESTTransactionLayer

{"uriPath": ["/","a", "b"], "uriQuery": {"rt": "test", "obs": "true"}"contentFormat": "application/link-format+json","options": {}"method": "GET","payload": null,"response": {

"status": "Success","contentFormat": "application/link-format+json","payload": "[{"href":"","rel":"self","rt":"test"}]"}

}

CommonCRUD

(IP)

Send/Rcv

(PHY)

Send/Rcv

URI Topic,URI

(IP)

Send/Rcv

(PHY)

(IP)

Pub/Sub

(PHY)

(IP)

Trx

(PHY)

URIURI

REST REST REST

CoAP HTTP MQTT WS CCML

URI

RESTREST

• MapabstractiontoHTTPandCoAPrequestandresponses• EncapsulatetheabstractioninWSandMQTTpayloads

ConsistentResourceIdentifiers:Cross-ProtocolHyperlinking

http://example.com:8000/b31/env/light/onoff

coap://example.com:5683/b31/env/light/onoff

ws://example.com:80/b31/env/light/onoff

mqtt://example.com:1883/b31/env/light/onoff

Mapped toURI

Mapped toURI

PartTopic--- PartPayload

EncapsulatedinPayload

ModelBasedHypertextAnnotation

PropertyEvent Action

(Capability)

Subscription

Notification

Actuation

Thing

Index

Capability

Notification

Capability

Index

has

pointsTo

DomainSchemaandModel• ReusabletermswithmayHaveandusedBydefinitions– “brightness”isusedby“light”butnot“motionsensor”– “brightness”mayhave“change”actionbutnot“open”

class: brightness,type: capability,description: “brightness control”usedBy: [ light ],mayHave: [

currentBrightness, targetBrightness,stepBrightness, moveBrightness, change, step, move, stop, propertyValueChange ],

params: {_targetValue: _targetBrightness,_stepSize: _stepBrightness,_moveRate: _moveBrightness},}

DomainModelExample

"@context": "http://thingschema.org","resource": [{

"type": "light","name": "light","capabilities": [

{"type": "brightness","name": "brightness"

},{"type": "onoff","name": "onoff"

}

DemonstratorandReferenceImplementation

• MachineHypermediaToolkitisanopensourcereferenceimplementation

https://github.com/connectIOT/MachineHypermediaToolkit

• DemonstratorresourceonGithubfortutorialintroduction

https://github.com/connectIOT/HypermediaDemo

Resources…• Theseslideshttp://www.slideshare.net/MichaelKoster/research-topics-in-machine-hypermedia• BlogArticlehttp://iot-datamodels.blogspot.com/2015/10/hypermedia-design-for-machine-interfaces.html• DemoResourcehttps://github.com/connectIOT/HypermediaDemo• ReferenceImplementation(workinprogress)https://github.com/connectIOT/MachineHypermediaToolkit• CoREInterfaceshttps://datatracker.ietf.org/doc/draft-ietf-core-interfaces/• Link-Formathttps://tools.ietf.org/html/rfc6690 ,https://tools.ietf.org/html/draft-ietf-core-links-json-04• SenML-01https://datatracker.ietf.org/doc/draft-jennings-core-senml/01/