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sequence.md

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Sequence

This extension defines two attributes that can be included within a CloudEvent to describe the position of an event in the ordered sequence of events produced by a unique event source.

The sequence attribute represents the value of this event's order in the stream of events. The exact value and meaning of this attribute is defined by the sequenceType attribute. If the sequenceType is missing, or not defined in this specification, event consumers will need to have some out-of-band communication with the event producer to understand how to interpret the value of the attribute.

Attributes

sequence

  • Type: String
  • Description: Value expressing the relative order of the event. This enables interpretation of data supercedence.
  • Constraints
    • REQUIRED
    • MUST be a non-empty lexicographically-orderable string
    • RECOMMENDED as monotonically increasing and contiguous

sequenceType

  • Type: String
  • Description: Specifies the semantics of the sequence attribute. See the SequenceType Values section for more information.
  • Constraints:
    • OPTIONAL
    • If present, MUST be a non-empty string

SequenceType Values

This specification defines the following values for sequenceType. Additional values MAY be defined by other specifications.

Integer

If the sequenceType is set to Integer, the sequence attribute has the following semantics:

  • The values of sequence are string-encoded signed 32-bit Integers.
  • The sequence MUST start with a value of 1 and increase by 1 for each subsequent value (i.e. be contiguous and monotonically increasing).
  • The sequence wraps around from 2,147,483,647 (2^31 -1) to -2,147,483,648 (-2^31).