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Purviews

For the RC to route requests to the appropriate DAPs, it must know what data each DAP contains. Thus, on the RC-DAP handshake, the DAP sends the RC the following information describing the data it contains:

The labels and time range make up a DAP's purview. This is the means by which the RC determines data locality when making routing decisions.

Labels

You define labels in the assembly configuration file. They are arbitrary key-value pairs that are meant to be user-friendly tags describing the kind of data held in the assembly's DAPs. Labels can be used to target particular assemblies in queries (see: Routing). The examples below show the labels section of multiple assembly files:

# Market data assemblies covering different asset classes, exchanges and countries.
labels:
  class: equity
  exchange: nyse
  country: usa

labels:
  class: futures
  exchange: nasdaq
  country: usa

labels:
  class: equity
  exchange: tsx
  country: canada

...

# Sensors data assemblies covering different sensor types.
labels:
    sensorType: electric

labels:
    sensorType: gas

...

Labels

  • An assembly must have at least one label, but there is no maximum number.
  • Two assemblies with the same labels are considered to have the same data (this can be used for redundancy). They can only be disambiguated in a query by using scope.
  • Labels need not have a consistent set of label keys; the RC treats any missing labels as null (see Routing).
  • If KXI_SG_ALLOW_OLD_LABEL_STYLE is true, then label names should not match any API parameter names.

Temporal purview

A DAP's temporal purview refers to the time range which it covers. It is expressed as two timestamps.

  • startTS - inclusive start time of the data the DAP covers
  • endTS - exclusive end time of the data the DAP covers

Unlike labels, the temporal purview of a DAP changes over time as data migrates across tiers at end-of-interval (EOI) and end-of-day (EOD) events. When such events occur, the DAPs automatically update the RC of the change in their temporal purview.

Null timestamps

  • Data published with null partition column values will fall outside DAP's purviews and render the data unqueryable, publishing such data should be avoided.