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.
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. spec: labels: class: equity exchange: nyse country: usa spec: labels: class: futures exchange: nasdaq country: usa spec: labels: class: equity exchange: tsx country: canada ... # Sensors data assemblies covering different sensor types. spec: labels: sensorType: electric spec: labels: sensorType: gas ...
- 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).
- Labels need not have a consistent set of label keys; the RC treats any missing labels as null (see Routing).
- Label keys should not use the names of tables or columns in the assembly's schema.
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.