IoT Semantics

Linked data

http://linkeddata.org/

Linked Data STRUCTURED DATA ON THE WEB

Resource Description Framework (RDF)

https://www.w3.org/RDF/

Json-ld

Json for linked data http://json-ld.org/

Example of an observation @type eddystoneBrodcast, @id eddystoneBroadcast

{
    "proximityarea": "",
    "eddystoneTlmAdvCnt": 0,
    "guestusers": [],
    "targetthings": "[]",
    "location": "",
    "eddystoneTlmVbatt": 0,
    "eddystoneTlmSecCnt": 0,
    "lastSeenByBLEHub": "2016-02-21T18:39:21.000Z",
    "eddystoneType": "uid",
    "eddystoneNamespace": "0123456789",
    "eddystoneInstance": "123456",
    "eddystoneTlmVersion": "0",
    "smoothingResult": "new",
    "description": "",
    "topic": "m2mBridgeTest/bleScanner/eddystone/new",
    "beaconRssi": 1,
    "@type": "/amtech/linkeddata/types/composite/observation/eddystoneBrodcast",
    "beaconTxPower": 1,
    "beaconDistance": 0,
    "creationDate": "2016-03-24T20:53:47.369Z",
    "guesttenants": [],
    "eddystoneUrl": "",
    "eddystoneTlmTemperature": 0,
    "producer": "eddystone",
    "detectiontime": "2016-03-04T18:37:31.000Z",
    "occurrencetime": "2016-03-04T18:37:31.000Z",
    "@id": "/amtech/things/observations/eddystoneBroadcast"
}

Things and Observations semantic

Semantic for things and the observations they produce can be defined using the Thing Types and Observation Types. This configurable semantic is composed by :

• Type general info (name, description, geometric representation)
• Type specific properties known as supported properties
• In the case of the thing types, the set of observation types that the given thing type can produce

Each specific property contains its own semantic to define. The main common information are:

• Value type or range: type of the values this property can hold
• property informations: name, caption, description, default values,etc
• Validation parameters and message (see below).
• Translation of the caption, description, validation message to the supported languages

Also, the thing types allow

• Maximum number and recording frequency of historic values (snapshots) to keep for the property, this is the information that will be shown in the timeline view
• an option to check if the thing type is allowed to have floor plan that can be helpful when working with proximity areas.

The validation parameters include

• minimum and maximum values for numerical data
• minimum and maximum date for datetime data
• regular expression for strings
• isRequired to say that the field can not be empty.
• JSON schema see Thing type SNMPDevice property setOIDs JSON schema validation

   {
       "type": "array",
       "items": {
           "type": "object",
           "properties": {
               "oid": {
                   "type": "string",
                   "pattern": ""
               },
               "type": {
                   "type": "string",
                   "enum": ["Integer", "OctetString", "Null", "ObjectIdentifier", "Sequence", "IpAddress", "Counter", "Gauge", "TimeTicks", "Opaque", "NsapAddress", "Counter64", "NoSuchObject", "NoSuchInstance", "EndOfMibView", "PDUBase"]
               },
               "value": {
                   "type": "string"
               }
           },
           "required": ["oid", "type", "value"]
       }
   }

To create a new supported property click on under the supportedProperties collection of the chosen semantics. The opened dialog allows to define the name of the property and the value type:

Select property type

As shown, there are 4 options

• the value type must be one of the proposed primitive types

Select primitive type

• the value must be an instance of any of the already defined thing types
• the property will hold thing types
• the property will hold instances of the thing type selected in the dialog

The choice will then appear on the right of the button

The three last options allow also to define the property as a collection:

Clicking on the button will create the new property and will open it on the editor so you can edit the other information of its semantics.

Thing and Observation instances

Instances are resources of a specific semantic type, that have values for each property defined in the semantics.

• Support instances enrichment, allowing to insert new properties and values after semantic been extended.

Publishing semantic

The semantics for thing and observation types can be defined without letting others see the changes. The action of publishing a type is what makes it visible to other creators, thus available for use by others in their activities. Once published, a type can only be extended by its creator.

When a type is published:

• it becomes visible to other creators that will be able to use it in their activities
• its supported properties become visible to other creators
• supported properties can only be added as long as they are not required
• existing supported properties that are required cannot be deleted if instances exist. If they are not required or no instances of the type exist, they can be deleted anytime
• the type can be deleted only if it is not used by any other resource
• values for the validation of the supported properties that are published cannot be changed : min value, max value, min date, max date and validation regex

public

*public types show this icon in the Tree editor

Policies for updating and deleting published semantic

Once a type is published, the following policies apply to the update and delete of its supported properties

• Required properties cannot be deleted or added if instances of the type exist
• Properties related to the validation of a supported property cannot be changed if the supported property is published and instances of the type exist. These properties are :
  • validationRegEx
  • validationSchema
  • minValue and maxValue for numeric supportedProperties
  • minDate and maxDate for datetime supportedProperties

Resource status

Resources have a status "draft" or "valid" according to validations of it properties against the metadata. If at least one property does not meet the conditions such as min value or validation regex, the resource status is set to draft. The status is a system-maintained property. It is updated every time a property value changes, or when the resource is explicitly validated. Validations can be performed by users that have only guest access to a resource, and even in that case, the system will use the result of the validation to update the status.

The execution of an observer does not return resources with invalid status, and therefore these resources are not taken into account in a reasoner execution.

Properties data type in custom semantics

• Support for using same property ID, with different data types in different Thing/Observation types

The supported properties of the user defined semantic have the scope of the type. This allows to define a supported property with the same ID in different types, with different meaning (data type). For instance: a thing type Truck with a property Weight of type double, and a thing type Container with a property Weight of type integer, that keeps not relation to the Truck weight other than having the same ID.

• Restriction of not reusing a property name with a different data type inside a Thing/Observation after property deletion

Once a supported property is defined inside a Thing or Observation type, using a data type, it cannot be redefined with another data type for the same Thing/Observation (even if the property is deleted from the type and then re-created). This is due to a restriction imposed by the graph data layer (Titan) (to be fixed in future releases)