Command-Line Workflow#


In Datumaro, most command-line commands operate on projects, but there are also few commands operating on datasets directly. There are 2 basic ways to use Datumaro from the command-line:

  • Use the convert, compare, merge commands directly on existing datasets.

  • Create a Datumaro project and operate on it:

Basically, a project is a combination of datasets, models and environment.

A project can contain an arbitrary number of datasets (see Datasets and Data Sources). A project acts as a manager for them and allows to manipulate them separately or as a whole, in which case it combines dataset items from all the sources into one composite dataset. You can manage separate datasets in a project by commands in the datum source command line context.

Note that modifying operations (transform, filter, patch) are applied in-place to the datasets by default.

If you want to interact with models, you need to add them to the project first using the model add command.

A typical way to obtain Datumaro projects is to export tasks in CVAT UI.

Project data model#


Datumaro tries to combine a “Git for datasets” and a build system like make or CMake for datasets in a single solution. Currently, Project represents a Version Control System for datasets, which is based on Git and DVC projects. Each project Revision describes a build tree of a dataset with all the related metadata. A build tree consists of a number of data sources and transformation stages. Each data source has its own set of build steps (stages). Datumaro supposes copying of datasets and working in-place by default. Modifying operations are recorded in the project, so any of the dataset revisions can be reproduced when needed. Multiple dataset versions can be stored in different branches with the common data shared.

Let’s consider an example of a build tree:


There are 2 data sources in the example project. The resulting dataset is obtained by simple merging (joining) the results of the input datasets. “Source 1” and “Source 2” are the names of data sources in the project. Each source has several stages with their own names. The first stage (called “root”) represents the original contents of a data source - the data at the user-provided URL. The following stages represent operations, which needs to be done with the data source to prepare the resulting dataset.

Roughly, such build tree can be created by the following commands (arguments are omitted for simplicity):

datum project create

# describe the first source
datum project import <...> -n source1
datum filter <...> source1
datum transform <...> source1
datum transform <...> source1

# describe the second source
datum project import <...> -n source2
datum model add <...>
datum transform <...> source2
datum transform <...> source2

Now, the resulting dataset can be built with:

datum project export <...>

Project layout#

├── .dvc/
├── .dvcignore
├── .git/
├── .gitignore
├── .datumaro/
│   ├── cache/ # object cache      └── <2 leading symbols of obj hash>/
│          └── <remaining symbols of obj hash>/
│              └── <object data>
│   │
│   ├── models/ # project-specific models   │
│   ├── plugins/ # project-specific plugins      ├── plugin1/ # composite plugin, a directory      |   ├──
│      |   └──
│      ├── # simple plugin, a file      └── ...
│   │
│   ├── tmp/ # temp files   └── tree/ # working tree metadata       ├── config.yml
│       └── sources/
│           ├── <source name 1>.dvc
│           ├── <source name 2>.dvc
│           └── ...
├── <source name 1>/ # working directory for the source 1   └── <source data>
└── <source name 2>/ # working directory for the source 2
    └── <source data>

Datasets and Data Sources#

A project can contain an arbitrary number of Data Sources. Each Data Source describes a dataset in a specific format. A project acts as a manager for the data sources and allows to manipulate them separately or as a whole, in which case it combines dataset items from all the sources into one composite dataset. You can manage separate sources in a project by commands in the datum source command line context.

Datasets come in a wide variety of formats. Each dataset format defines its own data structure and rules on how to interpret the data. For example, the following data structure is used in COCO format:

- ../../../images/<id>.jpg
- /annotations/

Datumaro supports complete datasets, having both image data and annotations, or incomplete ones, having annotations only. Incomplete datasets can be used to prepare images and annotations independently of each other, or to analyze or modify just the lightweight annotations without the need to download the whole dataset.

Check supported formats for more info about format specifications, supported import and export options and other details. The list of formats can be extended by custom plugins, check extending tips for information on this topic.

Use cases#

Let’s consider few examples describing what Datumaro does for you behind the scene.

The first example explains how working trees, working directories and the cache interact. Suppose, there is a dataset which we want to modify and export in some other format. To do it with Datumaro, we need to create a project and register the dataset as a data source:

datum project create
datum project import <...> -n source1

The dataset will be copied to the working directory inside the project. It will be added to the project working tree.

After the dataset is added, we want to transform it and filter out some irrelevant samples, so we run the following commands:

datum transform <...> source1
datum filter <...> source1

The commands modify the data source inside the working directory, inplace. The operations done are recorded in the working tree.

Now, we want to make a new version of the dataset and make a snapshot in the project cache. So we commit the working tree:

datum project commit <...>

At this time, the data source is copied into the project cache and a new project revision is created. The dataset operation history is saved, so the dataset can be reproduced even if it is removed from the cache and the working directory. Note, however, that the original dataset hash was not computed, so Datumaro won’t be able to compare dataset hash on re-downloading. If it is desired, consider making a commit with an unmodified data source.

After this, we do some other modifications to the dataset and make a new commit. Note that the dataset is not cached, until a commit is done.

When the dataset is ready and all the required operations are done, we can export it to the required format. We can export the resulting dataset, or any previous stage.

datum project export <...> source1
datum project export <...> source1.stage3

Let’s extend the example. Imagine we have a project with 2 data sources. Roughly, it corresponds to the following set of commands:

datum project create
datum project import <...> -n source1
datum project import <...> -n source2
datum transform <...> source1 # used 3 times
datum transform <...> source2 # used 5 times

Then, for some reasons, the project cache was cleaned from source1 revisions. We also don’t have anything in the project working directories - suppose, the user removed them to save disk space.

Let’s see what happens, if we call the compare command with 2 different revisions now.


Datumaro needs to reproduce 2 dataset revisions requested so that they could be read and compared. Let’s see how the first dataset is reproduced step-by-step:

  • source1.stage2 will be looked for in the project cache. It won’t be found, since the cache was cleaned.

  • Then, Datumaro will look for previous source revisions in the cache and won’t find any.

  • The project can be marked read-only, if we are not working with the “current” project (which is specified by the -p/--project command parameter). In the example, the command is datum compare rev1:... rev2:..., which means there is a project in the current directory, so the project we are working with is not read-only. If a command target was specified as datum compare <project>@<rev>:<source>, the project would be loaded as read-only. If a project is read-only, we can’t do anything more to reproduce the dataset and can only exit with an error (3a). The reason for such behavior is that the dataset downloading can be quite expensive (in terms of time, disk space etc.). It is supposed, that such side-effects should be controlled manually.

  • If the project is not read-only (3b), Datumaro will try to download the original dataset and reproduce the resulting dataset. The data hash will be computed and hashes will be compared (if the data source had hash computed on addition). On success, the data will be put into the cache.

  • The downloaded dataset will be read and the remaining operations from the source history will be re-applied.

  • The resulting dataset might be cached in some cases.

  • The resulting dataset is returned.

The source2 will be looked for the same way. In our case, it will be found in the cache and returned. Once both datasets are restored and read, they are compared.

Consider other situation. Let’s try to export the source1. Suppose we have a clear project cache and the source1 has a copy in the working directory.


Again, Datumaro needs to reproduce a dataset revision (stage) requested.

  • It looks for the dataset in the working directory and finds some data. If there is no source working directory, Datumaro will try to reproduce the source using the approach described above (1b).

  • The data hash is computed and compared with the one saved in the history. If the hashes match, the dataset is read and returned (4). Note: we can’t use the cached hash stored in the working tree info - it can be outdated, so we need to compute it again.

  • Otherwise, Datumaro tries to detect the stage by the data hash. If the current stage is not cached, the tree is the working tree and the working directory is not empty, the working copy is hashed and matched against the source stage list. If there is a matching stage, it will be read and the missing stages will be added. The result might be cached in some cases. If there is no matching stage in the source history, the situation can be contradictory. Currently, an error is raised (3b).

  • The resulting dataset is returned.

After the requested dataset is obtained, it is exported in the requested format.

To sum up, Datumaro tries to restore a dataset from the project cache or reproduce it from sources. It can be done as long as the source operations are recorded and any step data is available. Note that cache objects share common files, so if there are only annotation differences between datasets, or data sources contain the same images, there will only be a single copy of the related media files. This helps to keep storage use reasonable and avoid unnecessary data copies.