JSON Configuration
The configuration a simple JSON object containing the complete description of the behavior of the CEP engine (a set of EPL statements) and the mapping between the NGSI Context Entities and CEP Events.
Here is an example:
{
"host":"http://localhost:8080",
"in":[
{
"id":"Room.*",
"type":"Room",
"isPattern": true,
"attributes":[
{
"name":"temperature", "type":"double",
"metadata": [
{ "name":"unit", "type":"string" }
]
},
{ "name":"floor", "type":"string" }
]
"providers":[
"http://localhost:8081"
]
}
],
"out":[
{
"id":"FloorX",
"type":"Floor",
"attributes":[
{
"name":"temperature", "type":"double",
"metadata": [
{ "name":"unit", "type":"string" }
]
}
]
"brokers":[
{
"url":"http://orion.fiware.org:3000",
"serviceName": "tenant",
"servicePath": "test/example",
"authToken": "OAUTH_TOKEN"
}
]
}
],
"statements":[
"INSERT INTO Floor SELECT floor as id, avg(temperature) as temperature, temperature_unit FROM Room.win:time(10 min) GROUP BY floor OUTPUT LAST EVERY 10 sec"
]
}
Main sections
Host url
The host
url defined the HTTP address (scheme, host and port) where the Cepheus-CEP can be contacted.
It is used to subscribe to Context Providers (see next section).
Incomming events
The in
array defines the list of incoming events (NGSI Context Entities updates) the CEP expects as input from Context Providers.
Each Context Entity must be defined by:
id
: the ID of the Context Entity, can be a pattern ifisPattern
istrue
, mandatory.type
: the type of the Context Entity, mandatory.isPattern
: if theid
is a pattern, optional, default:false
.attributes
: the list of Context Attributes to match, mandatory, cannot be empty.providers
: the list of URL to Context Provider to subscribe for this Context Entity, optional.
Each Context Attributes is defined by:
name
: the name of the attribute, mandatory.type
: the type of the attribute, mandatory. Only simple types are supported for now :string
,double
,float
,int
,bool
.metadata
: the list of attribute Context Metadata, optional.jsonpath
: a jsonpath to allow accessing the value inside a "complex" object, optional.
Each Context Metadata is defined by:
name
: the name of the metadata, mandatory.type
: the type of the metadata, mandatory. Only simple types are supported for now :string
,double
,float
,int
,bool
.jsonpath
: a jsonpath to allow accessing the value inside a "complex" object, optional.
Outgoing events
The out
array defines the list of the outgoing events translated to Context Entities.
Each Context Entity must be defined by:
id
: the ID used by default for the Context Entity if the EPL statement does not define one, mandatory.type
: the type of the Context Entity, mandatory.isPattern
: if theid
is a pattern, optional, default:false
.attributes
: the list of Context Attributes to match, mandatory, cannot be empty.brokers
: the list of Brokers to notify.
Each Context Attributes is defined by:
name
: the name of the attribute, mandatory.type
: the type of the attribute, mandatory. Only simple types are supported for now :string
,double
,float
,int
,bool
.metadata
: the list of attribute Context Metadata, optional.
Each Context Metadata is defined by:
name
: the name of the metadata, mandatory.type
: the type of the metadata, mandatory. Only simple types are supported for now :string
,double
,float
,int
,bool
.
Each Brokers is defined by:
url
: the URL to the broker, mandatory.serviceName
: the value of theFiware-Service
HTTP header (required by Orion Broker), optional.servicePath
: the value of theFiware-ServicePath
HTTP header (required by Orion Broker), optional.authToken
: the value of theX-Auth-Token
HTTP header (required by PEP Proxy), optional.
Statements
The statements
array defines a list of Esper EPL statements
that will interact with the events previously defined.
Special fields
providers field
The providers
field controls how the CEP expect to receive incoming events.
There is two ways Context Providers can notify the CEP:
- The simplest way for the Context Provider is to send directly
/updateContext
requests to the CEP.
- The second way is to make the CEP subscribe to the Context Provider (like a Broker).
For each Context Provider the defined in the
providers
field of an event, the CEP will send initialy a/subscribeContext
, and will expect in return the Context Provider to notify it with/notifyContext
requests.
brokers field
Each outgoing event can have multiple brokers.
The CEP will send an ngsi10/updateContext
request to each broker for every outgoing event.
jsonpath field
The jsonpath
field of an Context Attribute or Context Metadata allows to extract
the value from a deeply nested structure using a JsonPath expression.
This works both for JSON and XML formats (with some limitations for the XML format).
For example, if an /updateContext
request sends the following payload:
{
"contextElements": [
{
"type": "Room",
"isPattern": "false",
"id": "Room1",
"attributes": [
{
"name": "temperature",
"type": "double",
"value": { "raw": ["16.2", "°C", "Celcus"] }
},
{
"name": "floor",
"type": "string",
"value": "1"
}
]
}
],
"updateAction": "UPDATE"
}
The 16.2
value can be extracted from the JSON object { "raw": ["16.2", "°C", "Celcus"] }
by using the JsonPath expression : $.raw[0]
.
Here is an example configuration to handle this payload by exposing the temperature value to the CEP:
{
"host":"http://localhost:8080",
"in":[
{
"id":"Room1",
"type":"Room",
"attributes":[
{ "name":"temperature", "type":"double", "jsonpath":"$.raw[0]" },
{ "name":"floor", "type":"string" }
]
}
],
"out":[
{
"id":"Floor1",
"type":"Floor",
"attributes":[
{ "name":"temperature", "type":"double" }
]
}
],
"statements":[
"INSERT INTO Floor SELECT floor as id, avg(temperature) as temperature FROM Room.win:time(10 min) GROUP BY floor OUTPUT LAST EVERY 10 sec"
]
}