Types

An SdsType, also called a type, defines the shape of a single measured event or object. A type gives structure to the data. For example, if a device measures three things, such as longitude, latitude, and speed, at the same time, then the SdsType should include those three properties.

An SdsType defines the structure of an event stored in an SdsStream and how to associate events within the SdsStream. An event is a single unit whose properties have values that relate to the index; that is, each property of an SdsType event is related to the event's index. Each event is a single unit.

SdsTypes can define simple atomic types, such as integers, floats, strings, arrays, and dictionaries, or complex types with nested SdsTypes using the Properties collection of an SdsType.

An SdsType used to define an SdsStream must have a key, which is a property, or a combination of properties that constitute an ordered, unique identity. Because the key is ordered, it functions as an index. It is known as the primary index. While a timestamp (DateTime) is a very common key, any ordered data can be used. Other indexes (secondary indexes), are defined in the SdsStream. For more details on indexes, see Indexes.

An SdsType is referenced by its identifier or Id field. SdsType identifiers must be unique within a Namespace. An SdsType can also refer other SdsTypes by using their identifiers. This enables type reusability. Nested types and base types are automatically created as separate types. For further information, see SdsType reusability.

Once an SdsType is created, it is immutable and its definition cannot be changed. If the SdsType definition is incorrect, you must delete and recreate it, and it can only be deleted if no streams, stream views, or other types reference it.

Only the SdsTypes used to define SdsStreams or SdsStreamViews are required to be added to the Sequential Data Store (SDS (Sequential Data Store)). SdsTypes that define properties or base types are contained within the parent SdsType do not need to be added to the Data Store separately.

SdsTypes define how events are associated and read within an SdsStream. When attempting to read non-existent indexes, indexes that fall between, before, or after existing indexes, the results are determined by the interpolation and extrapolation settings of the SdsType. For more information about interpolation and extrapolation, see Read characteristics.

SdsType fields and properties

The following table shows the SdsType fields. Fields that are not included are reserved for internal SDS (Sequential Data Store) use.

Rules for the type identifier (SdsType.ID)

The type identifier, SdsType.ID, has the following requirements:

• Is not case sensitive

• Can contain spaces

• Cannot contain forward slash ("/")

• Contains a maximum of 100 characters

Type management using the .NET SDS (Sequential Data Store) client libraries methods is performed through ISdsMetadataService. You can create ISdsMetadataService using one of the SdsService.GetMetadataService() factory methods. .NET client libraries provide SdsTypeBuilder to help build SdsTypes from .NET types.

SdsTypeProperty

The Properties collection defines each field in an SdsType. Type properties will appear in every stream that is created from a given type.

The following table shows the required and optional SdsTypeProperty fields. Fields that are not included are reserved for internal SDS (Sequential Data Store) use.

The SdsTypeProperty identifier has the same requirements as the SdsType identifier, which are:

• Is not case sensitive

• Can contain spaces

• Cannot contain forward slash ("/")

• Contains a maximum of 100 characters

IsKey

IsKey is a Boolean value that identifies the SdsType Key. Each SdsType needs a Key to function as the primary index.

A key defined by more than one property is called a compound key. A compound key can be defined by a maximum of three properties. In a compound key, each property that is included in the key is specified as IsKey. The Order field then defines how the keys are combined in the compound key.

Value

The Value field is used for properties that represent a value. For example, the named constant for an enum is a property with a value. When representing an enum in a SdsType, the SdsType properties collection defines the constant list for the enum. The SdsTypeProperty Identifier represents the name of the constant and the SdsTypeProperty value represents the value of the constant (see the enum State definitions below).

InterpolationMode

InterpolationMode is assigned when the property of the event should be interpolated in a specific way that differs from the interpolation mode of the SdsType. InterpolationMode is only applied to a property that is not part of the index. If the InterpolationMode is not set, the property inherits the InterpolationMode of the SdsType.

An SdsType with the InterpolationMode set to Discrete cannot have a property with an InterpolationMode. For more information on interpolation of events, see Read characteristics.

UOM

Uom is the unit of measure for the property. The Uom of a property may be specified by the name or the abbreviation. The names and abbreviations of UOM (Unit of Measure)s are case sensitive.

The InterpolationMode and Uom of a property can be overridden on the stream. For more information, see Streams.

Supported units of measure

For a list of units of measures that are supported for an SdsTypeProperty, see Supported units of measure.