How To Dev - How to perform Data Modeling


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How to proceed to the Entity Modeling / Data Modelling:

  • Create one or more Entity Instances / IoT Devices from a single Entity Model / IoT Device Model, by providing some information such as the Identification/name and other static variables (see example in the Figure above). In Snap4City, a large number of tools allow to
  • Any Entity Instance / IoT Device may change status and value over time, thus it may receive a large number of Entity Messages attached to it (see example in the Figure above). Those messages can describe the Entity Instance evolution over time of a set of attributes including:
    • state or versioning. For example, modelling a user profile, could change over time:  driving, sleeping, vacation, etc. 
    • variables or attributes (float, integer, etc.). For example, for a device modelling a Car we could have at a certain time and date (so called dateObserved, with value type = timestamp): position (lat, lon), velocity, acceleration, engine status, number of cycles per minute, travelled km, etc.
    • references to other Entity Instances / IoT Devices (in Snap4City, they coded as ServiceURI). For example, a Driver will have references to its own connected entities such as: DriverEvent, DriverHealthiness, and DriverAnalysis where information about tickets taken, analysis performed, changes of the driver license will be stored. Similarly, a Vehicle will have references to a VehicleEvent, with records for the maintenance of the vehicles, etc.
  • see:
  • see also:

Please note that, in all the Snap4City Entity Models (IoT Device Models): Nature and Subnature (classification), Lat/Lon (GPS positioning), and Device in Mobility (yes or not) attributes (variable) of Entities/Devices are not replicated in all the other models, since they are defined for default for all the Entity Models and for all the Smart Data Models as well. In the figure here below, the differences from Entity Model (IoT Device Model), one of its instances the registered Entity Instance (IoT device) “park45” and a specific message over time for the park45 device are put in evidence. Please note that for:

  • Entity Model (IoT Device Model): black strings are reporting model definition, while in red the set parameters for the model. In some cases, the model may not impose the protocol and broker.
  • Entity Instance (IoT Device): in instantiating the part45 device from its Model, a number of parameters in red has been imposed.
  • Entity Message (A temporal instance): a message over time (dateObserved, with value type = timestamp) and at a given location (GPS position) has been sent to the Entity Instance park45, also providing a set of changed values for the attributes/variables: FeeSlots, Humidity, Temperature, etc.

Figure: Example of Entity Model (IoT Device Model), Entity Instance (IoT Device) and
an Entity Message as temporal instance

  • create Data Model Diagrams which describes the relationships among Data/Entities, and in particular on Snap4City, among the Entities Instances and Entities Messages (see the last Figure, right).
    • Connecting different kind of Entities Instances/Messages via ServiceURI, SURI: in fact the actual connections can be among Entity Instances and/or Entities Messages. Thus, creating a sort of Interaction Diagram of UML. Connections among Entities can be:

Figure: Connections among Entities Instances and Message: the example reports
a static connection and dynamic connection to change the car at a given timestamp.
note also change of position and other parameters, if needed

  • Different kinds of relationships are possible depending on the Data Type used into the Entity Model (IoT Device Model), for example,
    • Single ServiceURI
    • Vector of ServiceURI (used only when simultaneous events occur, for example, list of changes performed to an Engine)
  • To each ServiceURI, it is possible to refer to any kind of Entity Instances (IoT Devices, Mobile Devices, POI, etc.), it is a sort of pointer/reference. Once obtained the reference it is possible to ask at the Entity to provide its last values (as well as the value at a given dateObserved, with value type = timestamp), and thus accessing to its definition, a sort of reflection model of high-level programming paradigms.
    • For example, this means that it is possible to have attributes as ServiceURI and attaching to it some Entity Instance and its Messages for describing the occurred event:
      • Analysis, Maintenance, Ticket, Illness, Vacation, etc.
  • Optionally: if you like you can create Entity Relationships diagrams among Entities, see UML, as a plus.

Figure: Example of a Dashboard and its graphical representation of the relationships among widgets, devices, Entity Instances and Entity Messages, etc.
The tool on the right side is called LOG, Linked Open Graph and it is accessible from the dialog of Dashboard manager.


The Snap4City tools for supporting the activity of Data Modelling are: