Execution engine

CEP (Complex Event Processing — now called Event Stream Processing)

AMTech execution engine is an implementation of a CEP; it encapsulates CEP's complexity in the DAP design.

Execution feedback and/or errors

When an activity is being executed by the execution engine an observationlifecycle type is sent to the activity_lifecycle topic. Some events are reported through the property event, among this events:

• Start of a reasoner (BEGIN)
• End of a reasoner (END)
• Execution errors (ERROR)

The following example illustrates activity "producer": "thingsInBoardroom" reporting action "resourceuri": "/amtech/activities/thingsInBoardroom/reasoners/createThingInBoardroomFromEddystoneBeacon/actions/ReportThingInBoardroom" started "event": "BEGIN"

    {
        "topic": "/activity_lifecycle/thingsInBoardroom",
        "guesttenants": [
            "_ALL"
        ],
        "event": "BEGIN",
        "@type": "/amtech/linkeddata/types/composite/observation/observationlifecycle",
        "producer": "thingsInBoardroom",
        "resourceuri": "/amtech/activities/thingsInBoardroom/reasoners/createThingInBoardroomFromEddystoneBeacon/actions/ReportThingInBoardroom",
        "detectiontime": "Tue Apr 26 21:41:09 UTC 2016",
        "@id": "/amtech/things/observations/983c488f-c3d4-44ec-85f2-795428d12d83",
        "occurrencetime": "Tue Apr 26 21:41:08 UTC 2016"
    }

This is a strong mechanism you can use to trace the execution of your activities if, at a given moment, you think they are not working as expected.

Security context

When creating a reasoner, the user can configure where will the security info will be taken from for executing the observer and performing the actions of the reasoners.

Security from observation or service

Security from the observation that triggers the reasoners

• The observer will return only things that belong to the tenant of the observation.
• Actions that create resources (things, observations, notifications, etc) will initialize the security properties of the resource being created with the security info of the observation
• The actions will be executed using the tenant of the observation

Security from the service

THIS OPTION IS DISABLED AT THE MOMENT

• The observer will return all the things readable by the service (owned by the tenants or shared with them).
• For actions that create resources in a reasoner of type Foreach, the user can configure the security info to be copied to the new resource. The security info can be taken from the observation or from the thing being iterated in the foreach
• The actions will be executed using the service (representing all tenants subscribed to the service)
• Access policies to types are not enforced when executing actions. All actions performed by the topology will use the list of tenants subscribed to the service as only authorization info, so for accessing the resources, tenants and guest tenants will be checked against the list of tenants subscribed to the service, but types won't be checked since there is no info of actors available for a service.

Security for objects being created

Expected Behaviors

• A follower that is not able to create/update/delete a resource of a certain type, because he does not have the actors, will be able to do so by pushing an observation that triggers a reasoner with security from the service that creates/updated/deletes a resource of that type. (the execution of the action in the topology runs behind the service, thus, the tenants subscribed to it, without any specific user, thus no specific actors)

Check this section for further details.

Extension module

EPC

Electronic product code Tag Data Translation implemented according to the GS1 EPC Tag Data Translation 1.6 specification (http://www.gs1.org/epc/tag-data-translation-standard) Exposed as 2 JavaScript functions available for reasoner's JavaScript binding:

* epcEncode
* epcDecode

They support the following codings:

• SGTIN-96, SGTIN-198, SSCC-96, SGLN-96, SGLN-195, GRAI-96, GRAI-170, GSRN-96, GSRNP-96, GDTI-96, GDTI-174, GID-96.

Debug

(See check reasoner)

Geospatial libraries

A couple of libraries are available in JavaScript bindings:

• geolib
• terraformer

You can make use of these libraries using the variables geolib and terraformer that are initialized as follows:

 var geolib = require('geolib');
 var terraformer = require('terraformer');

Example binding location property to a new created geofence thing, using the location from observation and calculating a circle with 300 radius

function(observation)
{
    var location;
    //get wkt json
    var loc = JSON.parse(observation.location);
    //parse longitude and latitude from wkt text
    var point = terraformer.WKT.parse(loc.wkt);
    //create a circle with 100 metres radius
    var circle = new terraformer.Circle([point.coordinates[0], point.coordinates[1]], 100, 64);
    //create location wkt 
    location = terraformer.WKT.convert(circle.geometry);
    //wkt poligon location bind to created geofence thing
    return location;
}