What is ISA-TAB?
Investigation-Study-Assay tab-delimited format (ISA-TAB) is a format based on the ISA-TAB specification 
that is used to capture and communicate the complex metadata required to interpret investigations (experiments) employing combinations of technologies. Metadata in ISA-TAB format facilitates standards-compliant collection, curation, management, and reuse of datasets in a wide variety of life science domains. ISA-TAB builds on the existing paradigm that is Microarray Gene Expression - Tabular format (MAGE-TAB)-a tab-delimited format to exchange microarray data.
Investigations, Studies, and Assays are the three entities around which the ISA-TAB framework is built. Investigation is a higher-order object, whose primary role is to group related Studies. Study is the central unit, containing information on the subject under study, its characteristics and any treatments applied. A Study has associated Assays. Assays are measurements performed either on the whole initial subject or on a sample taken from the subject, which produce qualitative or quantitative data. Assays can be characterized as the smallest complete unit of experimentation producing data associated with a subject.
The ISA-TAB specification relies on the ISA data model to order and classify the metadata. The ISA data model uses the following three types of text files to capture the metadata:
- The Investigation file contains all of the information needed to understand the project context, overall goals, and means. An Investigation is a high-level concept that groups related Studies.
- The Study file(s) includes information on the subject under study, its characteristics, and any treatments applied. A Study is the central unit and has associated Assays.
- The Assay file(s) include test steps and analytical measurements. An Assay is a test performed either on material taken from the subject or the whole initial subject, which produces qualitative and quantitative measurements (data).
Each of these files is a tab-delimited text file that researchers can create, view, and edit.
For more information about how the Investigation, Study, and Assay data are linked in the ISA-TAB format, refer to LinkedISA: Semantic Representation of ISA-Tab Experimental Metadata.
The following image shows the structure of the ISA data model.
Source: ISA-Tools.org 
Introduction to the CSSI DCC Portal
The CSSI DCC is a public repository for archive files that describe a scientific investigation, its study or studies, and each study's assay(s). Archives in this repository are in the standard Investigation-Study-Assay tab-delimited format (ISA-TAB) format; this format allows you to curate, manage, and reuse your own datasets and those that others create. For more information on the ISA-TAB format, refer to the ISA-TAB specification .
You can download the full archive files for any public investigation without logging in. Full archive files include the metadata describing the investigation, its study or studies, and each study's assay(s) and any data files associated with the investigation. You can download the full archive, metadata, and selected data files separately.
