Distributed Annotation System (DAS) is widely used communication protocol to implement decentralized annotation of genomic or protein sequences. DAS is built on a client–server architecture in which a single client integrates information from multiple servers. DAS provides two types of servers, namely, reference and annotation servers. Reference servers maintain the biological reference entity, for example, a nucleotide or peptide sequence. Annotation servers make additional information available that is related to the reference sequence, for instance, information on exons or protein domains. DAS registry service maintains a list of available DAS servers and it allows registry and discovery of DAS servers. Currently DAS registry maintains hundreds of servers including WormBase, FlyBase, Ensembl, TIGR, UCSC, and UniProt. The communication between server and client is performed using formatted URL requests and XML responses. Initially client send request to DAS registry which provides a list of reference and annotation servers. Further client obtains sequence information from reference server and later acquires sequence feature from each annotation server.

Although original DAS protocol was designed for sharing of genomic data, DAS continues to evolve and now it support other types of biological data through DAS extension bundle. Latest version of bundle (version 1.53E) includes extensions for sharing of data related to molecular interactions, 3D structural coordinates and others. Recently Blankenburg et al. had introduced the Distributed Annotation System for Molecular Interactions(DASMI). DASMI is not restricted to protein interactions and considers both experimentally determined and predicted interactions. DASMI architecture is similar to the decentralized client-server architecture of the Distributed Annotation System (DAS) and consists of a DAS extension for molecular interaction data exchange, interaction data servers, and visualization clients. DAS extension provides XML representations of molecular interactions (DASINT) which is flexible enough to allow many types of interactions. The DASINT XML document contains a list of interactions and a list of the interacting entities (or “interactors”), with each interaction referencing two or more interactors. In addition to standard attributes such as name and database source, both interactions and interactors may be further described with additional custom properties. Compared to other XML formats such as PSI-MI XML2.5, DASINT format is lightweight and flexible.

Schematic DASMI system architecture