4.3. Creating and modifying catalogues
A catalogue is a text file containing the translation rules of the
public identifier to system's files.
They make it easy to use DocBook, for they allow each user to have
their files installed in a different place (e.g. your home directory,
/usr/local/sgml, or in any other
place) though no other change on the document is necessary for it to be
processed and "compiled".
As in the example above, to associate an identifier to a file just
follow the sequence shown:
Copy the identifier PUBLIC
Type the identifying text
Indicate the path to the associated file
4.3.1. Explaining the terminology system
Notice the identifier
"-//Conectiva SA//DTD books V1.0//EN" |
Its formation is not random and follows some pre-defined
conditions.
The token "-" indicates that the used identifier isn't a
registered type. Only a few identifiers are registered and those usualy
belong to entities like ISO, IEEE,
and others.
The second part of the identifier defines the name of the
organization that created it. On the example above, Conectiva S.A.
The one before the last defines the contents (in this case a
DTD) and the name of the identified
text.
The last element indicates the language in which the document was
written. Since DocBook is a DTD written in English, the language is
EN. The two letter code recommended is the
ISO identification of the language.
More information can be obtained at OASIS Technical Resolution
9401:1997 (Amendment 2 to TR 9401).
4.3.2. Useful commands for catalogues
The most common commands to be used on catalogues are:
- PUBLIC
The keyword PUBLIC maps
public identifiers for identifiers on the system.
- SYSTEM
The SYSTEM keyword maps
system identifiers for files on the system.
- SGMLDECL
The keyword SGMLDECL designates the
system identifier of the SGML statement that should be used.
- DTDDECL
Similar to the SGMLDECL the
keyword DTDDECL identifies the SGML statement
that should be used. DTDDECL makes the
association of the statement with a public identifier to a
DTD. Unfortunately, this association isn't
supported by the open source tools available. The benefits of this
statement can be achieved somehow with multiple catalogue files.
- CATALOG
The keyword CATALOG allows a catalogue
to be included inside another. This is a way to make use of several
different catalogues without the need to alter them.
- OVERRIDE
The keyword OVERRIDE informs whether an
identifier has priority over a system identifier.
The standard on most systems is that the system identifier
has priority over the public one.
- DELEGATE
The keyword DELEGATE allows the
association of a catalogue to a specific type of public identifier.
The clause DELEGATE is very similar to the
CATALOG, except for the fact that it doesn't do
anything until a specific pattern is specified.
- DOCTYPE
If a document starts with a type of document, but
has no public identifier and no system identifier the clause
DOCTYPE associates this document
with a specific DTD.
