Concepts

Iris is a lightweight and flexible platform that aims to integrate all steps of an OCR workflow to produce the best possible text from scanned input pages.

Tasks

Each atomic function of iris is a single task. On the most basic level iris is nothing more than a collection of tasks that can be combined in a multitude of ways to alter input documents.

A task can be everything from an abstract process, e.g. binarization, to a specific invocation of a particular program, e.g. the ocr_tesseract task. Some tasks are native python code while others call external software.

Celery

Executing singular tasks is rather useless. Celery is used to coordinate and distribute the execution of a set of tasks, commonly called a job. A job is nothing more than the execution of tasks in a predefined order and parallelization level.

Celery uses a message broker to communicate the tasks to be run to the machines of the compute cluster. This documentation will not explain the use of celery except on the most rudimentary leve. To learn more about celery peruse its documentation.

Storage

While celery can be used to distribute tasks it is unsuitable for file distribution. To ensure that each machine has access to the same data a common storage medium has to be used. Iris utilizes a simple directory on the file system for all its storage purposes which can be placed on a network file system like NFS to realize the synchronization between all machines in the cluster.

For single machine use a normal directory set apart from all other use is sufficient.

All tasks of a job usually operate inside a single subdirectory on the shared medium. This directory should be globally unique and ensures that there are no conflicts between jobs.