The Blocks architecture was previously defined in a series of Internet-Drafts describing the core architecture,[1] the BXXP application framework,[11] and the Simple Exchange Profile.[12] A conversational description of the design rational[13] for the BXXP application framework were also previously described.

      The protocol has been implemented as a series of 3 software modules that were then applied to several "deep wells" of information, including the SEC's EDGAR databases. The mixer software is implemented in the Tcl and PERL languages, the SpaceServer is implemented in Tcl and uses Verity, Oracle and other commercial datastores to store, index, and retrieve metadata. Finally, builders have been implemented in Tcl with the most significant focus being on builders that act as a web proxy with the Apache web server. Many of these modules have been described here at Mappa.Mundi Magazine.

Things We Left Out

      The metadata framework we have designed explicitly left out the definition of several key issues. In particular, we are schema and namespace agnostic, allowing a variety of metadata models to be defined. In the particular case of EDGAR and other metadata repositories we have used to test and develop software, no use of mechanisms such as RDF have been directly employed.

      The system of servers, mixers, and builders provide a distributed solution, but the solution is one of "islands of distribution." It is up to mixers and space servers to know the DNS address and port number of a particular server to communicate with. As such, the servers have not been stitched together into a truly distributed, coordinated global service.

      The true distribution of a metadata service is a subject of the second part of our architecture, known as the convergence model. The convergence model is used for replication of metadata from one server to another, and is also the basis for knowledge management and other metadata schema and discovery issues.

      Finally, while we have put in hooks for namespace administration in the Blocks protocol (see the Blocks eXtensible eXchange Service[14]), we have also deferred further specification of those issues until more operational experience has been gained. In particular, a mechanism for distributed management of the namespace is dependent on the infrastructure for both knowledge management and bulk replication. In the time-honored tradition of hosts.txt, we thus manually administer the namespace until a better solution is necessary.

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