FIWARE Context Broker

Pasquale Vitale
Engineering Ingegneria Informatica
FIWARE Contex Broker

Introduction
Managing Context Information at large scale
FIWARE Context Broker GE (implementation: Orion)
Creating and pulling data
Pushing data and notifications
Convenience operations

Managing Context Information at large scale
Context Information is represented through values assigned to attributes
The Context Broker is able to:
handle context information at large scale
enable your application to query on context information
subscribe to changes in context information that will be received through notifications
enable your application or other applications to modify the context information

Context Management in FIWARE
Context Information: the value of attributes that characterize those entities relevant to your application
NGSI API
Bus
• Location
• No. passengers
• Driver
• License plate
Citizen
• Name-Surname
• Birthday
• Preferences
• Location
• To Do list
Shop
• Location
• Business name
• Franchise
• Offerings
Applications/Services
Context Broker

A sensor in a
pedestrian street
The Public Bus Transport
Management system
A person from his smartphone
It’s too hot!
What’s the current temperature?
… but programmers should just care
about entities and their attributes
Context Information independent from the source
Context information may come from many sources using different interfaces and protocols …

Get notified when an update on context information takes place
Bus = “X”, last_stop = “A”,
arrived= “Yes”
push
Notify me when bus “X” arrives at
the bus stop “A”
API

Acting on devices can be as easy as changing the value of attributes linked to its corresponding entity
Street lamp = “lamp1”, status= “on”
Street Lamp lamp1.status “on”
API

FIWARE Context Broker GE: Orion
Main functions:
Context availability management - OMA NGSI-9 specs
Context management - OMA NGSI-10 specs
HTTP and REST-based
XML payload support
JSON payload support

Functions Operations
NGSI-9
• Register,
• Search,
• Subscribe for context sources
• registerContext
• discoverContextAvailability
• subscribeContextAvailability
• updateContextAvailabilitySubscription
• unsubscribeContextAvailability
NGSI-10
• Query,
• Update,
• Subscribe to context elements
• updateContext
• queryContext
• subscribeContext
• updateContextSubscription
• unsubscribeContextSubscription

Context in NGSI is based in an entity-attribute model:
Attributes
• Name
• Type
• Value
Entity
• EntityId
• EntityType 1 n
“has”

Orion Architecture
11
Orion Context Broker
Context
Producers
Context
Consumers
subscriptions
update
query
notify
notify
update
update
DB
1026
1026

Context Broker operations: create and pull data
Context Producers publish data/context elements by invoking the updateContext operation on a Context
Broker
Context Consumers can retrieve data/context elements by invoking the queryContext operation on a
Context Broker
Context Consumer
queryContext
Context Producer
updateContext
Context Broker
speed

Entity creation example: car create
updateContext operation with APPEND action type
POST localhost:1026/v1/updateContext
...
{
"contextElements": [
{
"type": "Car",
"isPattern": "false",
"id": "Car1",
"attributes": [
{
"name": "speed",
"type": "float",
"value": "98"
}
]
}
],
"updateAction": "APPEND"
}
200 OK
...
{
"contextResponses": [
{
"contextElement": {
"attributes": [
{
"name": "speed",
"type": "float",
"value": ""
}
],
"id": "Car1",
"type": "Car"
},
"statusCode": {
"code": "200",
"reasonPhrase": "OK"
}
}
]
}

Update context elements example: car updateContext
updateContext operation with UPDATE action type
...
{
{
"type": "Car",
"id": "Car1",
"attributes": [
{
"name": "speed",
"type": "float",
"value": "110"
}
]
}
],
"updateAction": "UPDATE"
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"name": "speed",
"type": "float",
"value": ""
}
],
"id": "Car1",
"type": "Car"
},
"statusCode": {
"code": "200",
}
}
]
}

Query context operation example: car queryContext
queryContext operation by Id
POST <cb_host>:1026/v1/queryContext
...
{
"entities": [
{
"type": "Car",
"id": "Car1"
}
]
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"name": "speed",
"type": "float",
"value": "110"
}
],
"id": "Car1",
"type": "Car"
},
"statusCode": {
"code": "200",
}
}
]
}

Entity creation example: room create
...
{
{
"type": "Room",
"id": "Room1",
"attributes": [
{
"name": "temperature",
"type": "float",
"value": "24"
},
{
"name": "pressure",
"type": "integer",
"value": "718"
}
]
}
],
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": ""
},
{
"name": "pressure",
"type": "integer",
"value": ""
}
],
"id": "Room1",
"type": "Room"
},
"statusCode": {
"code": "200",
}
}
]
}
Two attributes: temperature and pressure

Update context elements example: room updateContext
...
{
{
"type": "Room",
"id": "Room1",
"attributes": [
{
"type": "float",
"value": "25"
},
{
"name": "pressure",
"type": "integer",
"value": "720"
}
]
}
],
"updateAction": "UPDATE"
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": ""
},
{
"name": "pressure",
"type": "integer",
"value": ""
}
],
"id": "Room1",
"type": "Room"
},
"statusCode": {
"code": "200",
}
}
]
}
Update: temperature and pressure

Query context operation example: room queryContext
queryContext operation by Id
...
{
"entities": [
{
"type": “Room",
"id": “Room1"
}
]
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": "25"
},
{
"name": "pressure",
"type": "integer",
"value": "720"
}
],
"id": "Room1",
"type": "Room"
},
"statusCode": {
"code": "200",
}
}
]
}

queryContext operation by Id and attribute
...
{
"entities": [
{
"type": “Room",
"id": "Room1"
}
] ,
"attributes": [
"temperature"
]
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": "25"
}
],
"id": "Room1",
"type": "Room"
},
"statusCode": {
"code": "200",
}
}
]
}

Entity creation example: room create
...
{
{
"type": "Room",
"id": "Room2",
"attributes": [
{
"type": "float",
"value": “33"
},
{
"name": "pressure",
"type": "integer",
"value": “722"
}
]
}
],
}
200 OK
...
{
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": ""
},
{
"name": "pressure",
"type": "integer",
"value": ""
}
],
"id": "Room2",
"type": "Room"
},
"statusCode": {
"code": "200",
}
}
]
}
Append another room: Room2

queryContext operation by regex Room.*
...
{
"entities": [
{
"type": “Room",
"isPattern": “true",
"id": "Room.*"
}
] ,
"attributes": [
"temperature"
]
}
{
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": "25"
}
],
"id": "Room1",
"type": "Room"
},
"statusCode": {
"code": "200",
}
},
{
"contextElement": {
"attributes": [
{
"type": "float",
"value": “33"
}
],
"id": "Room2",
"type": "Room"
},
"statusCode": {
"code": "200",
}
}
]
}

Context Broker operations: push data
Context Consumers can subscribe to receive context information that satisfy certain conditions using the
subscribeContext. Such subscriptions may have a duration.
The Context Broker notifies updates on context information to subscribed Context Consumers by invoking
the notifyContext operation they export
subscription_id = subscribeContext (consumer, expr, duration)
Context Consumer
notifyContext (subscription_id, data/context)
Context Broker
Application

Context subscriptions example: ONTIMEINTERVAL
POST <cb_host>:1026/v1/subscribeContext
…
{
"entities": [
{
"type": "Room",
"id": "Room1"
}
],
"attributes": [
"temperature"
],
"reference": "http://<host>:<port>/publish",
"duration": "P1M",
"notifyConditions": [
{
"type": "ONTIMEINTERVAL",
"condValues": [
“PT10S"
]
}
]
}
200 OK
...
{
"subscribeResponse": {
"duration": "P1M",
"subscriptionId": "54dcb87fa85d63b107245ff1"
}
}
25
19

Context subscriptions example: ONCHANGE
POST <cb_host>:1026/v1/subscribeContext
…
{
"entities": [
{
"type": "Room",
"id": "Room1"
}
],
"attributes": [
"temperature"
],
"reference": "http://<host>:<port>/publish",
"duration": "P1M",
"notifyConditions": [
{
"type": "ONCHANGE",
"condValues": [
"temperature"
]
}
],
"throttling": "PT5S"
}
200 OK
...
{
"subscribeResponse": {
"duration": "P1M",
"subscriptionId": "51c0ac9ed714fb3b37d7d5a8",
"throttling": "PT5S"
}
}
25
19

Notification
POST http://<host>:<port>/publish
…
{
"subscriptionId" : "51c0ac9ed714fb3b37d7d5a8",
"originator" : "localhost",
"contextResponses" : [
{
"contextElement" : {
"attributes" : [
{
"name" : "temperature",
"type" : "float",
"value" : "19"
}
],
"type" : "Room",
"isPattern" : "false",
"id" : "Room1"
},
"statusCode" : {
"code" : "200",
"reasonPhrase" : "OK"
}
}
]
}

Convenience Operations
They are equivalent to previous standard operations in functionality
Avoid the need for POST-ing payloads in many cases or simplifying them considerably
Simple to write, more REST-like
They are not a substitute but a complement to standard NGSI operations
Four examples (there are many others):
Entities
Attributes
Subscriptions
Types

Entities
GET /v1/contextEntities/{entityID} Query Context Retrieves an entity
POST /v1/contextEntities/{entityID} Entity Creation Creates an entity
PUT /v1/contextEntities/{entityID} Update Context Updates an entity
DELETE /v1/contextEntities/{entityID} Delete Context Deletes an entity
GET all entities
GET /v1/contextEntities

Attributes
GET /v1/contextEntities/{entityID}/attributes/{attrID} Retrieves an attribute’s value
POST /v1/contextEntities/{entityID}/attributes/{attrID} Creates a new attribute for an entity
PUT /v1/contextEntities/{entityID}/attributes/{attrID} Updates an attribute’s value
DELETE /v1/contextEntities/{entityID}/attributes/{attrID} Deletes an attribute

Subscriptions
POST /v1/contextSubscriptions Creates a subscription
PUT / v1/contextSubscriptions/{subID} Updates a subscription
DELETE / v1/contextSubscriptions/{subID} Deletes a subscription

Entity types
GET /v1/contextTypes
Retrieve a list of all entity types currently in Orion, including their corresponding attributes
GET / v1/contextTypes/{typeID}
Retrieve attributes associated to an entity type
PRO TIP
GET /v1/contextTypes?collapse=true
Retrieves a list of all entity types without attribute info

Advanced features
Pagination
Compound attribute values
Metadata
Geo-location
Registrations & context providers
Entity service paths

Pagination
Pagination helps clients organize query and discovery requests with a large number of responses
Three URI parameters:
limit
- Number of elements per page (default: 20, max: 1000)
offset
- Number of elements to skip (default: 0)
details
- Returns total elements (default: "off")

Pagination
Example, querying the first 100 entries:
POST <orion_host>:1026/v1/queryContext?limit=100&details=on
The first 100 elements are returned, along with the following errorCode in the response:
"errorCode": {
"code": "200",
"details": "Count: 322",
}
Now there are 322 entities, we can keep querying the broker for them:
POST <orion_host>:1026/v1/queryContext?offset=100&limit=100

Compound attribute values
An attribute can have a structured value. Vectors and key-value maps are supported
It maps directly to JSON's objects and arrays
Example:
we have a car whose four wheels' pressure
we want to represent as a compound attribute for a car entity
we would create the car entity like this:
{
{
"type": "Car",
"id": "Car1",
"attributes": [
{
"name": "tirePressure",
"type": "kPa",
"value": {
"frontRight": "120",
"frontLeft": "110",
"backRight": "115",
"backLeft": "130"
}
}
]
}
],
}

Metadata
Users may attach metadata to attributes
Reserved metadatas: ID, Location, creDate and modDate
Examples:
…
"attributes": [
{
"type": "float",
"value": "26.5",
"metadatas": [
{
"name": "accuracy",
"type": "float",
"value": "0.9"
}
]
}
]
…
…
"attributes": [
{
"type": "float",
"value": "26.5",
"metadatas": [
{
"name": "average",
"type": "float",
"value": "22.4"
}
]
}
]
…
Context Element attributes
• Name
• Type
• Value
Context Element
• EntityId
• EntityType
n
“has”
1
Metadata
• Name
• Type
• Valuen
“has”
1

Geo-location
Entities can have an attribute that specifies its location
- Using a "location" metadata
Example:
create an entity called Madrid (of type "City")
with attribute "position" defined as location
POST <cb_host>:1026/v1/updateContext
{
{
"type": "City",
"id": "Madrid",
"attributes": [
{
"name": "position",
"type": "coords",
"value": "40.418889, ‐3.691944",
"metadatas": [
{
"name": "location",
"type": "string",
"value": "WGS84"
}
]
}
]
}
],
}
Coordinates for Madrid are:
• latitude 40.418889
• longitude 3.691944

Geo-located queries
Entities location can be used in queryContex using:
- FIWARE::Location as scopeType
- and an area specification as scopeValue
The area specification are:
- area internal to a circle, given its centre and radius
- area external to a circle, given its centre and radius
- area internal to a polygon, given its vertices
- area external to a polygon, given its vertices
{
"entities": [
{
"type": "Point",
"isPattern": "true",
"id": ".*"
}
],
"restriction": {
"scopes": [
{
"type" : "FIWARE::Location",
"value" : {
"polygon": {
"vertices": [
{
"latitude": "0",
"longitude": "0"
},
{
"latitude": "0",
"longitude": "6"
},
{
"latitude": "6",
"longitude": "6"
},
{
"latitude": "6",
"longitude": "0"
}
]
}
}
}
]
}
}

Geo-location - circle
Distances between:
- Madrid / Alcobendas 13.65 km
- Madrid / Leganes 12.38 km
Consider a radius of 13.5 km
…
{
"entities": [
{
"type": "City",
"id": ".*"
}
],
"restriction": {
"scopes": [
{
"value" : {
"circle": {
"centerLatitude": "40.418889",
"centerLongitude": "‐3.691944",
"radius": "13500"
}
}
}
]
}
}
The query is Madrid and Leganes

Geo-location - inverse circle
Distances between:
- Madrid / Alcobendas 13.65 km
- Madrid / Leganes 12.38 km
Consider a radius of 13.5 km
{
"entities": [
{
"type": "City",
"id": ".*"
}
],
"restriction": {
"scopes": [
{
"value" : {
"circle": {
"centerLatitude": "40.418889",
"centerLongitude": "‐3.691944",
"radius": "13500",
"inverted": "true"
}
}
}
]
}
}
The query is Alcobendas

Registration & Context Providers
Context Broker doesn't cache the result of the query internally
Application
Context Broker Context Provider
1. registerContext(provider= )
2. queryContext(id) 3. queryContext(id)
4. data5. data
Context Consumer
db

POST <cb_host>:1026/v1/registry/registerContext
…
{
"contextRegistrations": [
{
"entities": [
{
"type": "Car",
"id": "Car1"
},
"attributes": [
{
"name": "speed",
"type": "float",
"isDomain": "false"
}
],
"providingApplication": "http://contextprovider.com/Cars"
}
],
"duration": "P1M"
}
200 OK
...
{
"duration" : "P1M",
"registrationId" : "52a744b011f5816465943d58"
}
The application registers the Context Provider for the Car1 speed using providingApplication attribute
Application
registerContext
http://contextprovider.com/Cars

{
{
"contextElement": {
"attributes": [
{
"name": "speed",
"type": "float",
"value": "100"
}
],
"id": "Car1",
"type": "Car"
},
"statusCode": {
"code": "200",
"details": "Redirected to context provider http://contextprovider.com/Cars",
}
}
]
}
It includes details in the response
...
{
"entities": [
{
"type": "Car",
"id": "Car1"
}
]
}
queryContext(id)
data

Multitenancy
Context Broker implements a simple multitenant/multiservice model based and logical database separation
Make easer service/tenant based authorization policies provided by other FI-WARE components or third
party software
Orion uses the "Fiware-Service" HTTP header in the request to identify the service/tenant
Example:
Fiware-Service: Tenant1
Context
Broker
Context
Broker
Tenant1
Tenant2
…
entities1/attributes1/subscripitions1
entities2/attributes2/subscripitions2

Entity Service Paths
Orion Context Broker supports hierarchical scopes
Entities can be assigned to a scope at creation time with updateContext
queryContext can be also scoped to locate entities in the corresponding scopes
For example, consider the following scopes in the figure:
- Madrid, as first level scope
- Gardens and Districts, as second-level scope (children of Madrid)
- ParqueNorte, ParqueOeste and ParqueSur (children of Gardens)
and Fuencarral and Latina (children of Districts)
- Parterre1 and Parterre2 (children of ParqueNorte)

In order to use a service path we put in a new HTTP header called “Fiware-ServicePath". For example:
Fiware-ServicePath: Madrid/Gardens/ParqueNorte/Parterre1
ParqueNorte
Parterre2Parterre1

Properties:
1. A query on a service path will look only into the specified node
2. Use ParentNode/# to include all child nodes
3. Queries without Fiware-ServicePath resolve to /#
4. Entities will fall in the "/" node by default
5. You can OR a query using a comma (,) operator in the header
For example, to query all street lights that are either in ParqueSur or in ParqueOeste you would use:
ServicePath: Madrid/Gardens/ParqueSur, Madrid/Gardens/ParqueOeste
You can OR up to 10 different scopes
- Maximum scope levels: 10
Scope1/Scope2/.../Scope10
1. You can have the same element IDs in different scopes (be careful with this!)
2. You can't change scope once the element is created
3. One entity can belong to only one scope
A B
A or B
ParqueNorte
Parterre1
light1
light1

FIWARE Context Broker

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