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 you create a reasoner, a dialog appears where you should select a name and an execution behavior. In the case where the execution behavior is to visit all the things returned by the observer, you should also select the security context under which the reasoner will run. Two different options are available:

Security from observation or service

• Observation's security context.

  It means that the observer will return only those things readable by the tenant of the observation. Also, all actions that create objects (things, observations, notifications, etc) will initialize the security context of the object being created with the security context of the observation being consumed.

• Service's security context.

  It means that the observer will return all the things readable by the service. Also, all actions that create objects (things, observations, notifications, etc) will ask you to select between the security context of the observation being consumed and the security context of the thing being visited as the security context of the object being created.

Security for objects being created

Extension module

EPC

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;
}