Release Name: XML-Based Clinical Experiment Data Exchange Schema (XCEDE) 2.0

The XCEDE schema provides an extensive metadata hierarchy for describing and documenting research and clinical studies. The schema organizes information into five general hierarchical levels:
•a complete project
•studies within a project
•subjects involved in the studies
•visits for each of the subjects
•the full description of the subject's participation during each visit

Each of these sub-schemas is composed of information relevant to that aspect of an experiment and can be stored in separate XML files or spliced into one large file allowing for the XML data to be stored in a hierarchical directory structure along with the primary data. Each sub-schema also allows for the storage of data provenance information allowing for a traceable record of processing and/or changes to the underlying data. Additionally, the sub-schemas contain support for derived statistical data in the form of human imaging activation maps and simple statistical value lists.
XCEDE was originally designed in the context of neuroimaging studies and complements the Biomedical Informatics Research Network (BIRN) Human Imaging Database, an extensible database and intuitive web-based user interface for the management, discovery, retrieval, and analysis of clinical and brain imaging data. This close coupling allows for an interchangeable source-sink relationship between the database and the XML files, which can be used for the import/export of data to/from the database, the standardized transport and interchange of experimental data, the local storage of experimental information within data collections, and human and machine readable description of the actual data.
The core XCEDE schema supports several major extensible components:
•A flexible experimental hierarchy: As illustrated in the above, the XCEDE experiment hierarchy consists of several levels (project, subject, visit, study, episode and acquisition) representing divisions of experiment data at various granularities. Elements at each level contain level-specific "info" elements, whose schema types may be derived to store experiment-specific or data modality-specific metadata. The linking mechanism between levels is flexible enough to support the omission of levels if the schema user finds them unnecessary.
•Experimental protocols: Specifications for order, number and time of experimental components (e.g. assessments within a clinical interview, scans within a scanning session, visits within a project) are supported using a generic protocol element.
•Event data: XCEDE has elements to support time-interval-annotated metadata such as behavioral stimulus/response data, per-timepoint QA metrics, etc.
•Data provenance: The complete history of a processing stream can be stored and propagated using provenance elements provided by the XCEDE schema.
•Plus: application-specific file and analysis lists (catalogs), interfaces to binary data, arbitrary user and application annotations, derived data, and more.