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Introduction

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Once we have an update time for a dataset's resources, we can calculate its age and combined with the update frequency, we can ascertain the freshness of the dataset.

Dataset Aging Methodology

A resource's age can be measured using today's date - last update time. For a dataset, we take the lowest age of all its resources. This value can be compared with the update frequency to determine an age status for the dataset.

Thought had previously gone into classification of the age of datasets. Reviewing that work, the statuses used (up to date, due, overdue and delinquent) and formulae for calculating those statuses are sound so they have been used as a foundation. It is important that we distinguish between what we report to our users and data providers with what we need for our automated processing. For the purposes of reporting, then the terminology we use is simply fresh or not fresh. For contacting data providers, we must give them some leeway from the due date (technically the date after which the data is no longer fresh): the automated email would be sent on the overdue date rather than the due date. The delinquent date would also be used in an automated process that tells us it is time for us to manually contact the data providers to see if they have any problems we can help with regarding updating their data.

Update Frequency	Dataset age state thresholds (how old must a dataset be for it to have this status)
	Fresh		Not Fresh
	Up-to-date	Due	Overdue	Delinquent
Daily	0 days old	1 day old due_age = f	2 days old overdue_age = f + 2	3 days old delinquent_age = f + 3
Weekly	0 - 6 days old	7 days old due_age = f	14 days old overdue_age = f + 7	21 days old delinquent_age = f + 14
Fortnightly	0 - 13 days old	14 days old due_age = f	21 days old overdue_age = f + 7	28 days old delinquent_age = f + 14
Monthly	0 -29 days old	30 days old due_age = f	44 days old overdue_age = f + 14	60 days old delinquent_age = f + 30
Quarterly	0 - 89 days old	90 days old due_age = f	120 days old overdue_age = f + 30	150 days old delinquent_age = f + 60
Semiannually	0 - 179 days old	180 days old due_age = f	210 days old overdue_age = f + 30	240 days old delinquent_age = f + 60
Annually	0 - 364 days old	365 days old due_age = f	425 days old overdue_age = f + 60	455 days old delinquent_age = f + 90
Never	Always	Never	Never	Never
Live	Always	Never	Never	Never
As Needed	Always	Never	Never	Never

Here is a presentation about data freshness from January 2017 that provides a good introduction.

Data Freshness Architecture

Data freshness consists of a database, REST API, freshness process and freshness emailer.

There is a docker container hosting the Postgres database (https://hub.docker.com/r/unocha/alpine-postgres/ - 201703-PR116) and a port is open on there to allow connection from external database clients (hdxdatateam.xyz:5432). There is a another Docker container (https://hub.docker.com/r/mcarans/alpine-haskell-postgrest/) that exposes a REST API to the database (http://hdxdatateam.xyz:3000/) - the docker setup for this is here: https://github.com/OCHA-DAP/alpine-haskell-postgrest. The freshness process and freshness emailer are also within their own Docker containers. The docker-compose that brings all these containers together is here: https://github.com/OCHA-DAP/hdx-data-freshness-docker.

Here is an overall view of the architecture:

Drawio