Data sanity rules

[richfab]

What is the issue and why is it an issue?

Following the discussion in #106, consensus was reached to create a separate issue to discuss whether rules that verify data sanity should be added to the validator (ie: validation rules that are not part of the spec).

Examples of data sanity rules can be:

• station capacity value should not be lower than num_vehicles_available + num_docks_available
• reservation_price_flat_rate should be in cents
• etc

Open questions are:

• Should the validator remain a canonical validator (only validate rules that are part of the spec) or should it also help producers detect errors in the content of their data?
• What process or rationale should determine what these rules and their threshold values should be?
• Who shall bear the burden of maintaining these rules over time?

Please describe some potential solutions you have considered (even if they aren’t related to GBFS).

The code for a dozen data sanity rules can be found in the commits of #106. This code will be removed from that PR to separate data sanity rules (not part of the spec) and data compliance rules (part of the spec).

[tdelmas]

• the last_updated timestamp should not be in the future

As the specification says about last_updated: "Indicates the last time data in the feed was updated. ", I would argue that alast_updated in the future does break the specification.

A clearer example of "validation rules that are not part of the spec" could be "the unlock price is < 100€": that rule is not part of the specification, but could detect systems where "€ cents" and € were confused.

[richfab]

I would argue that a last_updated in the future does break the specification.

You are right @tdelmas. I have updated the issue descriptions to keep this rule in #106. Thank you!