Types

The Sequential Data Store (SDS) stores streams of events and provides convenient ways to find and associate events. Events are stored in streams. A primitive type is available in CONNECT data services and is used within the API and REST definitions to identify a stream type.

You can define simple atomic types, such as integers, floats, strings, arrays, and dictionaries, or complex or nested types using the properties collection of SdsTypes. For more information, see SdsType fields and properties.

A type that is used to define a stream must have a key. A key is a SdsTypes property (or a combination or properties) that constitutes an ordered, unique identity. If the key is ordered so it functions as an index, it is known as the primary index. While a timestamp (DateTime) is a very common type of index, any type that can be ordered is permitted. Secondary and other indexes are defined in the stream. For more information, see Indexes.

Consider how the events will be represented in a stream, as the type defines each event in a stream. An event is a single unit with properties that have values related to the index; that is, each property of a type event is related to the event's index. Each event is a single unit.

Reference a type by its identifier or Id field. Type identifiers must be unique within a namespace.

A type can also refer to other types by using their identifiers. This referencing enables type re-usability. Nested types and base types are automatically created as separate types. For more information, see Type reuse.

Types define how events are read and associated within a collection of streams. The read characteristics when attempting to read non-existent indexes—indexes that fall between, before, or after existing indexes—are determined by the interpolation and extrapolation settings of the type. For more information about read characteristics, see Interpolation and Extrapolation.

Types are immutable. After a type is created, its definition cannot be updated. The type must be deleted and recreated if the definition is incorrect. You can delete a type only if no streams, stream views, or other types reference it.

Only the types that are used to define streams or stream views are required to be added to SDS. Types that define properties or base types are contained within the parent type so they do not need to be added to SDS independently.