In the scope of this document, we will use the following terms:
An Open Catalog that includes only comments and CATALOG directives pointing to other catalogs (or DELEGATE directives if supported).
A Document Type Definition. It specifies the syntax used in documents. Examples of well-known DTDs include: HTML, XHTML, DocBook, TEI, MathML, MusicML, etc. SGML and XML give a framework for writing DTDs.
A set of directives defined by the OASIS TR9401 Catalog, mostly used for defining equivalences between FPIs (Formal Public Identifiers) and real file names (see TR9401:1997 on http://www.oasis-open.org).
A set of files assembled together for distribution. It includes RPMs, DEBs and any other kind of packaging system.
Any program used to view, edit, convert, use or apply any kind of treatment to a document written using a SGML or XML DTD (Document Type Definition). This includes command-line utilities as well as GUI-based applications.
Declarations or scripts that define formatting during some conversion or edition process of a SGML or XML document. They can be written in any style sheets language: CSS, DSSSL, FOSIs, XSL, ...
An Open Catalog pointing to all the centralized catalogs.