Datalad Metadata Model

This software implements the metadata model that datalad and datalad-metalad will use in the future (datalad-metalad>=0.3.0) to handle metadata.

Model Elements (the model layer)

The metadata model is defined by the API of the top-level classes. Those are:

• MetadataRootRecord -- holds top-level metadata information for a single version of a datalad dataset

• UUIDSet -- holds metadata root records for a set of datasets that are identified by their UUIDs and their version.

• TreeVersionList -- holds metadata root records and a sub-dataset tree for a dataset version and its sub-datasets

• Metadata -- represents metadata for a single item, i.e. dataset or file. Metadata is associated with extractor names and extraction parameters.

• DatasetTree -- a representation of the sub-dataset hierarchy of a dataset

• FileTree -- a representation of the file-tree of a dataset

• ...

Because of the large size of some datalad-datasets, e.g. tens of thousands of sub-datasets and hundres of millions of files, the implementation allows focus-based operations on individual parts of the potentially very large metadata model. The implementation uses the proxy-pattern, that means, it loads, modifies, and saves only the minimal necessary model elements that are necessary to operate on the metadata-information that the user is interested in.

Storage layer

The model elements have to be persisted on a storage backend. How the model is mapped on storage backends is defined by the storage layer, that is to a large degree independent of the model layer. The intention is to support multiple storage backends in the past.

Currently only one storage backend is supported:

• git-mapping -- a storage backend that stores a metadata model in a git repository. The model objects are stored outside of existing branches. They are referenced by datalad-specific git-references under refs/datalad/*