What is the specific definition of a point and how to use it?

[georghi...@gmail.com]

Hi all, 

here are two questions / discussion points I want to share:

I have a physical device, that is a multisensor (Lumin, AirQual,Temp). Would it make sense to put the sensor below equipment and then the measurements as point? I am confused on how to use points consistently.

In the brick literature it says:

Point: Points are physical or virtual entities that generate timeseries data. Physical points include actual sensors and setpoints in a building, whereas virtual points encompass synthetic data streams that are the result of some process which may operate on other timeseries data, e.g. average floor temperature sensor. source (p. 6)

At the same time when looking on the ontology i see eg. Gas Meter under Equipment. So what's the specific definition of a point? 

Thanks for your help, 

Georg

[Heye]

Hi,

this is a very good question. What is throwing me off is that Points are defined, as you quoted, to be "physical or virtual entities". When is a sensor or meter a point and when should it be an equipment? To me it would make sense if a measurement can only be done by a Point and a Point must always be connected to an equipment that is the physical entity that measures it. So would we have a relation like this:

Device A brick:Gas_Meter

Sensor A brick:Gas_Sensor

Device brick:hasPoint Sensor

Is that correct?

Furthermore, I wonder, would one consider the Sensor in this case be a virtual entity and when would a Point be a physical entity?

Best

Heye

[Gabe Fierro]

Hi there!

Meters are equipment, but they host the points like the power/energy sensor that point to the actual data. We are in the process of trying to clean up the specific relationship between meters and equipment so that it is clear that the power/energy from the equipment is being monitored/metered/measured by the meter equipment. In the past, I have used "feeds" to relate an equipment (e.g. chiller) to the meter to indicate that the chiller's energy or water consumption is being measured by that meter, but it is becoming clear that we need a more straightforward way of accomplishing that. We also need to have a more consistent way of modeling submeter hierarchies. This will be discussed in the Ontology working groups (https://brickschema.org/blog/working-groups/)

We also have a gap when it comes to describing the physical location of sensors. When a Point "isPointOf" a Location, it is similar to saying where the data is observed/measured. However, this doesn't say anything about where the sensor device is physically located.

Device A brick:Gas_Meter

Sensor A brick:Gas_Sensor

Device brick:hasPoint Sensor

Is that correct?

Yes, that is the correct approach.

Best,

Gabe

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[Oskar Nilsson]

Coming back to the original question. As I understand it the multisensor is a kind of equipment that has various points. If the multisensor is in Room12 how does one best capture that? Should the points be "pointOf" both the multisensor and the room? Correspondingly, is there a generic SPARQL graph pattern to find the temperature in a specific room?

[Gabe Fierro]

The most natural model would be to associate the points with the multisensor, rather than the room, though of course you could do both.

You could then use a SPARQL query to find the temperature for a room no matter "where" it is in the model:

SELECT ?sensor  WHERE {

   <bldg:room1> brick:hasPart?/brick:hasPoint ?sensor .

  ?sensor rdf:type/rdfs:subClassOf* brick:Air_Temperature_Sensor .

[Oskar Nilsson]

Thanks! If the multisensor is located in the room, shouldn't it be "isLocationOf?" instead of "hasPart?" in the query?

[Gabe Fierro]

You are right! I was working on some equipment composition stuff so I got some wires crossed. Correct query is:

SELECT ?sensor  WHERE {

   <bldg:room1> brick:isLocationOf?/brick:hasPoint ?sensor .

  ?sensor rdf:type/rdfs:subClassOf* brick:Air_Temperature_Sensor .

}