+ <sect3 id="tools.cql.pqf"><title>CQL to PQF conversion</title>
+ <para>
+ Conversion to PQF (and Z39.50 RPN) is tricky by the fact
+ that the resulting RPN depends on the Z39.50 target
+ capabilities (combinations of supported attributes).
+ Furthermore, the CQL and SRW operates on index prefixes
+ (URI or strings), whereas the RPN uses Object Identifiers
+ for attribute sets.
+ </para>
+ <para>
+ The CQL library of &yaz; defines a <literal>cql_transform_t</literal>
+ type. It represents a particular mapping between CQL and RPN.
+ This handle is created and destroyed by the functions:
+ <synopsis>
+cql_transform_t cql_transform_open_FILE (FILE *f);
+cql_transform_t cql_transform_open_fname(const char *fname);
+void cql_transform_close(cql_transform_t ct);
+ </synopsis>
+ The first two functions create a tranformation handle from
+ either an already open FILE or from a filename.
+ </para>
+ <para>
+ The handle is destroyed by <function>cql_transform_close</function>
+ in which case no further reference of the handle is allowed.
+ </para>
+ <para>
+ When a <literal>cql_transform_t</literal> handle has been created
+ you can convert to RPN.
+ <synopsis>
+int cql_transform_buf(cql_transform_t ct,
+ struct cql_node *cn, char *out, int max);
+ </synopsis>
+ This function converts the CQL tree <literal>cn</literal>
+ using handle <literal>ct</literal>.
+ For the resulting PQF, you supply a buffer <literal>out</literal>
+ which must be able to hold at at least <literal>max</literal>
+ characters.
+ </para>
+ <para>
+ If conversion failed, <function>cql_transform_buf</function>
+ returns a non-zero error code; otherwise zero is returned
+ (conversion successful).
+ </para>
+ <para>
+ If you wish to be able to produce a PQF result in a different
+ way, there are two alternatives.
+ <synopsis>
+void cql_transform_pr(cql_transform_t ct,
+ struct cql_node *cn,
+ void (*pr)(const char *buf, void *client_data),
+ void *client_data);
+
+int cql_transform_FILE(cql_transform_t ct,
+ struct cql_node *cn, FILE *f);
+ </synopsis>
+ The former function produces output to a user-defined
+ output stream. The latter writes the result to an already
+ open <literal>FILE</literal>.
+ </para>
+ </sect3>
+ <sect3 id="toolq.cql.xcql"><title>CQL to XCQL conversion</title>
+ <para>
+ Conversion from CQL to XCQL is trivial and does not
+ require a mapping to be defined.
+ There three functions to choose from depending on the
+ way you wish to store the resulting output (XML buffer
+ containing XCQL).
+ <synopsis>
+int cql_to_xml_buf(struct cql_node *cn, char *out, int max);
+void cql_to_xml(struct cql_node *cn,
+ void (*pr)(const char *buf, void *client_data),
+ void *client_data);
+void cql_to_xml_stdio(struct cql_node *cn, FILE *f);
+ </synopsis>
+ Function <function>cql_to_xml_buf</function> converts
+ to XCQL and stores result in a user supplied buffer of a given
+ max size.
+ </para>
+ <para>
+ <function>cql_to_xml</function> writes the result in
+ a user defined output stream.
+ <function>cql_to_xml_stdio</function> writes to a
+ a file.
+ </para>
+ </sect3>