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    Types: TextFile
    Names: »documents.tex«

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\chapter	{The ISO Documents Database}\label{isodocuments}
The database \file{/usr/etc/isodocuments} contains a simple mapping between
textual descriptions of FTAM document types and the various object
identifiers which compose each document type.

The database itself is an ordinary ASCII text file containg information
regarding the known FTAM document types on the host.
Each line contains
\begin{itemize}
\item	the entry number of the document type, a simple string;

\item	the document type, an object identifier;

\item	the constraint set, an object identifier;

\item	the abstract syntax, an object identifier;
and,

\item	the transfer syntax, an object identifier
\end{itemize}

Blanks and/or tab characters are used to seperate items.
However,
double-quotes may be used to prevent separation between arguments.
The sharp character (`\verb"#"') at the beginning of a line indicates a
commentary line.

\f

\section	{Accessing the Database}
The \man libftam(3n) library contains the routines used to access the database.
These routines ultimately manipulate an \verb"isodocment" structure,
which is the internal form.
\begin{quote}\index{isodocument}\small\begin{verbatim}
struct isodocument {
    char   *id_entry;

    OID     id_type;
    OID     id_constraint;
    OID     id_abstract;
    OID     id_transfer;
};
\end{verbatim}\end{quote}
The elements of this structure are:
\begin{describe}
\item[\verb"id\_entry":] the entry number of the document type;

\item[\verb"id\_type":] the document type;

\item[\verb"id\_constraint":] the constraint set;

\item[\verb"id\_abstract":] the abstract syntax;
and,

\item[\verb"id\_transfer":] the transfer syntax.
\end{describe}

The routine \verb"getisodocument" reads the next entry in the database,
opening the database if necessary
\begin{quote}\index{getisodocument}\small\begin{verbatim}
struct isodocument *getisodocument ()
\end{verbatim}\end{quote}
It returns the manifest constant \verb"NULL" on error or end-of-file.

The routine \verb"setisodocument" opens and rewinds the database.
\begin{quote}\index{setisodocument}\small\begin{verbatim}
int     setisodocument (f)
int     f;
\end{verbatim}\end{quote}
The parameter to this procedure is:
\begin{describe}
\item[\verb"f":] the ``stayopen'' indicator,
if non-zero, then the database will remain open over subsequent calls to the
library.
\end{describe}
The routine \verb"endisodocument" closes the database.
\begin{quote}\index{endisodocument}\small\begin{verbatim}
int     endisodocument ()
\end{verbatim}\end{quote}
Both of these routines return non-zero on success and zero otherwise.

There are two routines used to fetch a particular entry in the database.
The routine \verb"getisodocumentbyentry" maps textual descriptions into
the internal form.
\begin{quote}\index{getisodocumentbyentry}\small\begin{verbatim}
struct isodocument *getisodocumentbyentry (entry)
char   *entry;
\end{verbatim}\end{quote}
The parameter to this procedure is:
\begin{describe}
\item[\verb"entry":] the descriptor of the object.
\end{describe}
and returns the \verb"isodocument" structure describing that document.
On failure, the manifest constant \verb"NULL" is returned instead.

The routine \verb"getisodocumentbytype" performs the inverse function.
\begin{quote}\index{getisodocumentbytype}\small\begin{verbatim}
struct isodocument *getisodocumentbytype (tpye)
OID     type;
\end{verbatim}\end{quote}
The parameter to this procedure is:
\begin{describe}
\item[\verb"type":] the identifier of the document.
\end{describe}
On a successful return,
an \verb"isodocument" structure describing the document is returned.