The Metacat Server stores arbitrary XML documents in a relational database without foreknowledge of the document schema. It does this by implementing the DOM within the table structure of the relational database. Metacat also performs optimized free-text and structured searches across the entire document collection. Metacat provides standardized interfaces to client software for document processing, storing and searching.

Metacat provides several means of access for communicating with the server to access and submit metadata and data. First, users can access the flexible web user interface. Second, the servlet can be queried using basic HTML forms. Third, a client API exists for writing software for accessing the server's contents.

When accessing the servlet interface either through 'GET' or 'POST' HTTP requests, the request is directed to the appropriate handler based on an 'action' parameter in the request. For example, using the parameter 'action=getversion' one could construct an HTTP GET request to retrive the Metacat version string:
http://some.metacat.host/context/metacat?action=getversion

The complete list of "actions" which can be used in request to Metacat along with the additional parameters associated with each action are as follows.

Primary actions for the most important features:

• action=login
  • username
  • password
• action=logout
• action=query
  • meta_file_id
  • returndoctype
  • filterdoctype
  • returnfield
  • owner
  • site
  • operator
  • casesensitive
  • searchmode
  • anyfield
  • sessionid
  • Any other parameter passed in will be interpreted as a query term unless it is listed in the 'query.ignored.params' property in metacat.properties
• action=squery
  • query
  • qformat
• action=read
  • docid
  • qformat
• action=insert
  • docid
  • doctext
  • dtdtext
• action=update
  • docid
  • doctext
  • dtdtext
• action=delete
  • docid

• action=spatial_query
  • xmin
  • xmax
  • ymin
  • ymax
  • skin
• action=export
  • docid
• action=readinlinedata
  • inlinedataid
• action=validate
  • valtext
  • docid
• action=setaccess
  • docid
  • principal
  • permission
  • permType
  • permOrder
  • principal
• action=getaccesscontrol
  • docid
• action=getprincipals
• action=getdoctypes
• action=getdtdschema
  • doctype
• action=getlastdocid
  • scope
  • username
• action=getrevisionanddoctype
  • docid
• action=getversion
• action=getlog
  • ipaddress
  • principal
  • docid
  • event
  • start
  • end
• action=buildindex
  • docid
• action=shrink