Harvesting is the process of automatically fetching remote metadata (ie. from other data portals or not) and storing them into udata to be able to search and find them.


  • Backend: designate a protocol implementation to harvest a remote endpoint.
  • Source: it’s a remote endpoint to harvest. Each harvest source is caracterized by a single endpoint URL and a backend implementation. A harvester is configured for each source.
  • Job: designate a full harvesting for a given source.
  • Validation: each created harvester needs to be validated by the admin team before being run.


After a harvester for a given source has been created and validated, it will run either on demand or periodically.

A harvesting job is done in three separate phases:

  1. initialize: the harvester fetches remote identifiers to harvest and create a single task for each.
  2. process: each task created in the initialize is executed. Each item is processed independently.
  3. finalize: when all tasks are done, the finalize is a closure for the job and mark it as done.

Harvested dataset will have the following extras properties:

Property Meaning
harvest:domain Domain on which dataset has been harvested (ex: data.test.org)
harvest:remote_id Dataset identifier on the remote repository
harvest:source_id Harvester identifier
harvest:last_update Last time this dataset has been harvested

Administration interface

You can see the harvester administration interface in the System view.

Administration harvester listing

You’ll have an overview of all harvesters and their state (pending validation, last run…)

Each harvester have a full job history with every remote harvested items.

Administration harvester details


All harvesting operations are grouped together into the harvest command namespace:

usage: udata harvest [-?]

Handle remote repositories harvesting operations

positional arguments:
    jobs                List started harvest jobs
    launch              Launch a source harvesting on the workers
    create              Create a new harvest source
    schedule            Schedule a harvest job to run periodically
    purge               Permanently remove deleted harvest sources
    sources             List all harvest sources
    backends            List available backends
    unschedule          Unschedule a periodical harvest job
    run                 Run a harvester synchronously
    validate            Validate a source given its identifier
    attach              Attach existing datasets to their harvest remote id
    delete              Delete a harvest source

optional arguments:
  -?, --help            show this help message and exit


udata comes with 3 harvest backends but you can implement your own backend.


This backend harvest any DCAT endpoint. This is now the recommended way to harvest remote portals and repositories (and so to expose opendata metadata for any portal and repository).

As pagination is not described into the DCAT specification, we try to detect some supported pagination ontology: - Hydra PartialCollectionView - Legacy Hydra PagedCollection

Fields are extracted according these rules:

Dataset fields

Dataset dcat:Dataset notes
title dct:title
description dct:description Detect and parse HTML as Markdown
tags dct:keyword + dct:theme
frequency dct:accrualPeriodicity
temporal_coverage dct:temporal See Temporal coverage
license N/A See License detection
resources dct:distribution Also match the buggy dct:distributions
Dataset.extras dcat:Dataset notes
dct:identifier dct:identifier
uri @id URI Reference if present

Resource fields

Resource dcat:Distribution notes
title dct:title If missing, guessed from URL or format
description dct:description Detect and parse HTML
url dcat:downloadURL or dcat:accessURL
published dct:issued
last_modified dct:modified
format dct:format
mime dcat:mediaType
filesize dcat:bytesSize
checksum spdx:checksum See Checksum

Temporal coverage

Temporal coverage can be expressed in many ways. This harvester try the following patterns: - DCAT-AP format using schema.org properties (schema:startDate and schema:endDate) - Gov.uk Time Interval parsing - ISO date interval as literal (ie. YYYY[-MM[-DD]]/YYYY[-MM[-DD]]) - A Single ISO month or year (ie. YYYY[-MM])


Checksum spdx:Checksum
type spdx:algorithm
value spdx:checksumValue

License detection

License is extracted from one of the DCAT distribution. The havester try to guess the license from dct:license and dct:right. The first match is kept. If none matches, no license is set on the dataset.


This backend harvests CKAN repositories/portals through their API and is available as a udata extension.


This backend harvests OpenDataSoft repositories/portals through their API (v1) and is available as a udata extension.


You can implement your own backends by extending udata.harvest.backends.BaseBackend and implementing the initialize() and process() methods.

A minimal harvester adding fake random datasets might looks like:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from udata.models import db, Resource
from udata.utils import faker

from udata.harvest.backends.base import BaseBackend

class RandomBackend(BaseBackend):
    display_name = 'Random'

    def initialize(self):
        '''Generate a list of fake identifiers to harvest'''
        # In a real implementation, you should iter over
        # a remote endpoint to list identifiers to harvest
        # and optionnaly store extra data
        for _ in range(faker.pyint()):
            self.add_item(faker.uuid4())  # Accept kwargs to store data

    def process(self, item):
        '''Generate a random dataset from a fake identifier'''
        # Get or create a harvested dataset with this identifier.
        # Harvest metadata are already filled on creation.
        dataset = self.get_dataset(item.remote_id)

        # In a real implementation you should :
        # - fetch the remote dataset (if necessary)
        # - validate the fetched payload
        # - map its content to the dataset fields
        # - store extra significant data in the `extra` attribute
        # - map resources data

        dataset.title = faker.sentence()
        dataset.description = faker.text()
        dataset.tags = list(set(faker.words(nb=faker.pyint())))

        # Resources
        for i in range(faker.pyint()):

        return dataset

You need to properly expose the harvester as a udata.harvesters entrypoint in your setup.py:

        'udata.harvesters': [
            'random = canonical.path.to_the:RandomBackend',

The easiest way is to start from the [dedicated cookiecutter template][cookiecutter-template]:

pip install cookiecutter
cookiecutter gh:opendatateam/cookiecutter-udata-harvester

This will create a new package with a harvester skeleton on which you can start hacking.

You may take a look at the existing backends to see exiting implementations.