Background and motivation


Data is at the core of science, and unobstructed access promotes scientific discovery through collaboration between data producers and consumers. The last years have seen dramatic improvements in availability of data resources for collaborative research, and new data providers are becoming available all the time.

However, despite the increased availability of data, their accessibility is far from being optimal. Potential consumers of these public datasets have to manually browse various disconnected warehouses with heterogeneous interfaces. Once obtained, data is disconnected from its origin and data versioning is often ad-hoc or completely absent. If data consumers can be reliably informed about data updates at all, review of changes is difficult, and re-deployment is tedious and error-prone. This leads to wasteful friction caused by outdated or faulty data.

The vision for this project is to transform the state of data-sharing and collaborative work by providing uniform access to available datasets – independent of hosting solutions or authentication schemes – with reliable versioning and versatile deployment logistics. This is achieved by means of a dataset handle, a lightweight representation of a dataset that is capable of tracking the identity and location of a dataset’s content as well as carry meta-data. Together with associated software tools, scientists are able to obtain, use, extend, and share datasets (or parts thereof) in a way that is traceable back to the original data producer and is therefore capable of establishing a strong connection between data consumers and the evolution of a dataset by future extension or error correction.

Moreover, DataLad aims to provide all tools necessary to create and publish data distributions — an analog to software distributions or app-stores that provide logistics middleware for software deployment. Scientific communities can use these tools to gather, curate, and make publicly available specialized collections of datasets for specific research topics or data modalities. All of this is possible by leveraging existing data sharing platforms and institutional resources without the need for funding extra infrastructure of duplicate storage. Specifically, this project aims to provide a comprehensive, extensible data distribution for neuroscientific datasets that is kept up-to-date by an automated service.

Technological foundation: git-annex

The outlined task is not unique to the problem of data-sharing in science. Logistical challenges such as delivering data, long-term storage and archiving, identity tracking, and synchronization between multiple sites are rather common. Consequently, solutions have been developed in other contexts that can be adapted to benefit scientific data-sharing.

The closest match is the software tool git-annex. It combines the features of the distributed version control system (dVCS) Git — a technology that has revolutionized collaborative software development – with versatile data access and delivery logistics. Git-annex was originally developed to address use cases such as managing a collection of family pictures at home. With git-annex, any family member can obtain an individual copy of such a picture library — the annex. The annex in this example is essentially an image repository that presents individual pictures to users as files in a single directory structure, even though the actual image file contents may be distributed across multiple locations, including a home-server, cloud-storage, or even off-line media such as external hard-drives.

Git-annex provides functionality to obtain file contents upon request and can prompt users to make particular storage devices available when needed (e.g. a backup hard-drive kept in a fire-proof compartment). Git-annex can also remove files from a local copy of that image repository, for example to free up space on a laptop, while ensuring a configurable level of data redundancy across all known storage locations. Lastly, git-annex is able to synchronize the content of multiple distributed copies of this image repository, for example in order to incorporate images added with the git-annex on the laptop of another family member. It is important to note that git-annex is agnostic of the actual file types and is not limited to images.

We believe that the approach to data logistics taken by git-annex and the functionality it is currently providing are an ideal middleware for scientific data-sharing. Its data repository model annex readily provides the majority of principal features needed for a dataset handle such as history recording, identity tracking, and item-based resource locators. Consequently, instead of a from-scratch development, required features, such as dedicated support for existing data-sharing portals and dataset meta-information, can be added to a working solution that is already in production for several years. As a result, DataLad focuses on the expansion of git-annex’s functionality and the development of tools that build atop Git and git-annex and enable the creation, management, use, and publication of dataset handles and collections thereof.


Building atop git-annex, DataLad aims to provide a single, uniform interface to access data from various data-sharing initiatives and data providers, and functionality to create, deliver, update, and share datasets for individuals and portal maintainers. As a command-line tool, it provides an abstraction layer for the underlying Git-based middleware implementing the actual data logistics, and serves as a foundation for other future user front-ends, such as a web-interface.