7.4 Catalog Files

A catalog file is a set of records mapping public and system identifiers to accessible resources.

PUBLIC
   "-//W3C//DTD XHTML 1.0 Strict//EN"
   "/home/dtds/xhtml1-strict.dtd"
SYSTEM
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
   "/home/dtds/xhtml1-strict.dtd"

It is a method of indirection.

An entity resolver of an application might consult a catalog file for locating replacements to public and system URI’S.
Catalog files allow to place the files anywhere we want, and ensuring their access just by managing the references to them in the catalog files.
XML 1.0 doesn’t offer a standard way for specifying catalogs.
OASIS Entity Management Catalog Technical Resolution TR9401:1997 proposes a syntax catalog entries for SGML.
OASIS introduced a working draft for XML catalog specifications

class MyEntityResolver implements EntityResolver {
   public MyEntityResolver( String cat ){
     try{
        FileReader myIn  = new FileReader( cat );
        // load catalog
     } catch(java.io.IOException e){ }
   }
   public InputSource resolveEntity (
                       String publicId, String systemId) {
     // search catalog
} }

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