Properties#

This section contains elaborations of the different fields in the properties sheet.

There are two types of properties in physical data model (DMS): Connection and Data. The Connection property is used to specify how nodes are connected, while the Data property is used to specify the data that is stored on the node. These concepts match a Entity and Literal in semantic modeling. It is recommended that you use PascalCase for views, neat uses camelCase for data properties. This makes it easier to distinguish between the two by looking at the Value Type column in the Properties sheet.

Data Property#

A data property is used to specify the data that is stored on the node (also known as node attributes). Below is an example of a data property:

View	View Property	Value Type	Container	Container Property
WindTurbine	capacity	float64(unit=power:megaw)	GeneratingUnit	capacity

This data property specifies that the WindTurbine view has a property called capacity that is a holding vLUW of type float64 with the unit power:megaw. The data is stored in the GeneratingUnit container with the property capacity.

To see which value types are supported, see the CDF API Spec for Container Creation section. The container.properties.type.type field specifies the type of the property.

There are two Value Type that supports extra parameters

float32 and float64 - These are used to specify floating-point numbers. The unit parameter is used to specify the unit of the number. See Units for available units. See example above.
enum - This is used to specify an enumeration. You need to set collection to the name of the enumeration and, optionally, unknownValue to the value that should be used when the value is unknown. See example below. When enumerations are used, there is expected to be a corresponding enum sheet in the physical data model file with the enumeration values.

View	View Property	Value Type	Container	Container Property
WindTurbine	category	enum(collection=category, unknownValue=onshore)	WindTurbine	category

Index#

For data properties, you can specify an index. The index is used to speed up queries on the property. The syntax is as follows:

View	View Property	Value Type	Container	Container Property	Index
WindTurbine	name	text	GeneratingUnit	name	btree:nameIndex(cursorable=True)

Note that you can specify whether the index is cursorable or not, see here.

You can also specify indices that uses multiple data properties. You can do this by specifying the same Index name for multiple properties. When you specify an index on multiple properties you must specify the order these properties should be used. See the example below:

View	View Property	Value Type	Container	Container Property	Index
WindTurbine	name	text	GeneratingUnit	name	inverted:nameCapacityIndex(order=1)
WindTurbine	capacity	float64	GeneratingUnit	capacity	inverted:nameCapacityIndex(order=2)

There are two available index types, btree which should be used for non-list properties and inverted which should be used for list properties. If you do not specify the index type, it will default to btree for non-list properties and inverted for list properties.

View	View Property	Value Type	Container	Container Property	Index
WindTurbine	tags	text	GeneratingUnit	name	inverted:tagsIndex

Connection Property#

All connections have a ValueType that specifies the type of the connected node. For example:

View	ViewProperty	Connection	Value Type	Is List
WindTurbine	blades	direct	Blade	True

This connection specifies that the WindTurbine view has a property called blades that is a direct relation to the Blade view. In addition, the Is List, specifies that there can be multiple blades connected to a wind turbine.

Connection Implementation#

The column Connection specifies how the connection is implemented in the CDF data model and can be one of the following:

Direct relation—This is cheap in terms of storage and query time.
Edge connection—This is more flexible, but more expensive in terms of storage and query time.
Reverse connection—This is used to specify a connection from the other end of a direct relation or edge connection.

To get more details on the difference, see the data modeling documentation. Note that in addition to the mentioned differences, direct relations have an upper limit of 1000 connection per node.

The syntax for the Connection column is as follows:

direct - This specifies a direct relation. There are no extra parameters. Note, however, that you need to specify Container and Container Property as direct connections are stored in the container.
edge - This specifies an edge connection. You can, optionally, specify type, properties, and direction as extra parameters.
reverse - This specifies a reverse connection. You need to specify the property that the connection is reversing.

Edge example:

View	ViewProperty	Connection	Value Type	Is List
WindTurbine	metmasts	edge(type=distance,properties=Distance,direction=outwards)	MetMast	True
Distance	distance		float64(unit=length:m)	False

This connection specifies that the WindTurbine view has a property called metmasts that is an edge connection to the MetMast view. The edges are of type distance and have properties stored in the Distance view. The Distance view has a property called distance that is a float64 with the unit length:m.

Why is both type and properties needed? The type specifies the type of the edge, this is used for filtering when querying the data model. The properties specifies the properties that are stored on the edge. This is used to store data on the edge. In the example above, we can, for example, write a query that returns all MetMast (Wheather Station) that are connected to a WindTurbine with a distance less than 100 meters.

Reverse example:

View	ViewProperty	Connection	Value Type	Is List
MetMast	windTurbines	reverse(property=metmasts)	WindTurbine	True

This connection specifies that the MetMast view has a property called windTurbines that is a reverse connection of the metmasts property in the WindTurbine view. The Is List specifies that there can be multiple wind turbines connected to a MetMast.

Connecting this example to the previous example, we see that the reverse here will be an edge that is pointing the opposite direction of the WindTurbine.metmasts edge. The reverse enable use to easily reuse the same edge for both directions.