Delineation from related solutions¶
To our knowledge, there is no other effort with a scope as broad as DataLad’s. Datalad aims to unify access to vast arrays of (scientific) data in a domain and data modality agnostic fashion with as few and universally available software dependencies as possible.
The most comparable project regarding the idea of federating access to various data providers is the iRODS-based INCF Dataspace project. IRODS is a powerful, NSF-supported framework, but it requires non-trivial deployment and management procedures. As a representative of data grid technology, it is more suitable for an institutional deployment, as data access, authentication, permission management, and versioning are complex and not-feasible to be performed directly by researchers. Datalad on the other hand federates institutionally hosted data, but in addition enables individual researchers and small labs to contribute datasets to the federation with minimal cost and without the need for centralized coordination and permission management.
Existing data-portals, such as DataDryad, or domain-specific ones (e.g. Human Connectome, OpenfMRI), concentrate on collecting, cataloging, and making data available. They offer an abstraction from local data management peculiarities (organization, updates, sharing). Ad-hoc collections of pointers to available data, such as reddit datasets and Inside-R datasets, do not provide any unified interface to assemble and manage such data. Data portals can be used as seed information and data providers for DataLad. These portals could in turn adopt DataLad to expose readily usable data collections via a federated infrastructure.
Data delivery/management middleware¶
Even though there are projects to manage data directly with dVCS (e.g. Git), such as the Rdatasets Git repository this approach does not scale, for example to the amount of data typically observed in a scientific context. Datalad uses git-annex to support managing large amounts of data with Git, while avoiding the scalability issues of putting data directly into Git repositories.
In scientific software development, frequently using Git for source code management, many projects are also confronted with the problem of managing large data arrays needed, for example, for software testing. An exemplar project is ITK Data which is conceptually similar to git-annex: data content is referenced by unique keys (checksums), which are made redundantly available through multiple remote key-store farms and can be obtained using specialized functionality in the CMake software build system. However, the scope of this project is limited to software QA, and only provides an ad-hoc collection of guidelines and supporting scripts.
The git-annex website provides a comparison of Git-annex to other available distributed data management tools, such as git-media, git-fat, and others. None of the alternative frameworks provides all of the features of git-annex, such as integration with native Git workflows, distributed redundant storage, and partial checkouts in one project. Additional features of git-annex which are not necessarily needed by DataLad (git-annex assistant, encryption support, etc.) make it even more appealing for extended coverage of numerous scenarios. Moreover, neither of the alternative solutions has already reached a maturity, availability, and level of adoption that would be comparable to that of git-annex.
Although it is possible, and intended, to use DataLad without ever invoking git or git-annex commands directly, it is useful to appreciate that DataLad is build atop of very flexible and powerful tools. Knowing basics of git and git-annex in addition to DataLad helps to not only make better use of DataLad but also to enable more advanced and more efficient data management scenarios. Datalad makes use of lower-level configuration and data structures as much as possible. Consequently, it is possible to manipulate Datalad datasets with low-level tools if needed. Moreover, Datalad datasets are compatible with tools and services designed to work with plain Git repositories, such as the popular GitHub service.
To better illustrate the different scopes, the following table provides an overview of the features that are contributed by each software technology layer.
|Version control (text, code)||✓||✓can mix||✓can mix|
|Version control (binary data)||(not advised)||✓||✓|
|Auto-crawling available resources||✓RSS feeds||✓flexible|
|Unified dataset handling||✓|
|Unified authentication interface||✓|