Metacat has the capability of proxying a connection to a data file server. This capability is provided through an abstract class called DataFileUploadInterface. Currently, there is a data file server implemented for this interface that can store non-XML data files on the local UNIX file system. Theoretically, any file storage system could be proxied through this interface.

Since Metacat has been designed as a metadata storage system for ecological data, there was a concern that data and metadata files were being stored seperately and that users would find it impractical to have to use two different systems to get their data and metadata. This system also allows users to specify access control restraints on their data files the same way that they are specified on the xml metadata files.

Metacat Server can retrieve data files that are stored on Metacat file system or in any other file system on Internet.
Metacat stores data files in a directory under the servlet context. It writes information about these data files in xml_documents just like about any XML file.
An example of HTTP request for download of data file on Metacat is shown below:

http://server.domain.com/metacat?action=read&docid=nceas.55

An example of HTTP request for download of data file on Internet is shown below:

http://server.domain.com/metacat?action=read&docid=http://otherserver.domain.com/filename

Note in docid=http://otherserver.domain.com/filename HTTP protocol is used, i.e. currently for file download HTTP protocol is only supported.

Data Upload (PUT) The insertion and update process for a data file is the same as the insertion process for an XML file.