-<!-- $Id: zoom.xml,v 1.6 2001-11-06 17:05:19 adam Exp $ -->
+<!-- $Id: zoom.xml,v 1.9 2001-11-15 08:58:28 adam Exp $ -->
<chapter id="zoom"><title>Building clients with ZOOM</title>
<para>
</para>
<para>
The lack of a simple Z39.50 client API for &yaz; has become more
- and more apparent over time. So when the first ZOOM specification
+ and more apparent over time. So when the first &zoom; specification
became available,
an implementation for &yaz; was quickly developed. For the first time, it is
now as easy (or easier!) to develop clients than servers with &yaz;. This
- chapter describes the ZOOM C binding. Before going futher, please
+ chapter describes the &zoom; C binding. Before going futher, please
reconsider whether C is the right programming language for the job.
There are other language bindings available for &yaz;, and still
more
- are in active development. See the ZOOM website at
- <ulink url="http://zoom.z3950.org/">zoom.z3950.org</ulink> for
+ are in active development. See the
+ <ulink url="http://zoom.z3950.org/">ZOOM website</ulink> for
more information.
</para>
that because of typedefs. All destroy methods should gracefully ignore a
<literal>NULL</literal> pointer.
</para>
+ <para>
+ In each of the sections below you'll find a sub section called
+ protocol behavior, that descries how the API maps to the Z39.50
+ protocol.
+ </para>
<sect1 id="zoom.connections"><title>Connections</title>
<para>The Connection object is a session with a target.
Otherwise, if <parameter>val</parameter> is
<literal>NULL</literal>,
the option is unchanged.
- The function returns the previous value of the option.
+ The function returns the (new) value of the option.
</para>
<table frame="top"><title>ZOOM Connection Options</title>
<tgroup cols="3">
<row><entry>
async</entry><entry>If true (1) the connection operates in
asynchronous operation which means that all calls are non-blocking
- except <function>Z3950_event</function>.
+ except
+ <link linkend="zoom.events"><function>Z3950_event</function></link>.
</entry><entry>0</entry></row>
<row><entry>
maximumRecordSize</entry><entry> Maximum size of single record.
holds messages for the error and additional-info if passed as
non-<literal>NULL</literal>.
</para>
+ <sect2><title>Protocol behavior</title>
+ <para>
+ The calls <function>Z3950_connection_new</function> and
+ <function>Z3950_connection_connect</function> establises a TCP/IP
+ connection and sends an Initialize Request to the target if
+ possible. In addition, the calls waits for an Initialize Response
+ from the target and the result is inspected (OK or rejected).
+ </para>
+ <para>
+ If <literal>proxy</literal> is set then the client will establish
+ a TCP/IP connection with the peer as specified by the
+ <literal>proxy</literal> host and the hostname as part of the
+ connect calls will be set as part of the Initialize Request.
+ The proxy server will then "forward" the PDU's transparently
+ to the target behind the proxy.
+ </para>
+ <para>
+ For the authentication parameters, if option <literal>user</literal>
+ is set and both options <literal>group</literal> and
+ <literal>pass</literal> are unset, then Open style
+ authentication is used (Version 2/3) in which case the username
+ is usually followed by a slash, then by a password.
+ If either <literal>group</literal>
+ or <literal>pass</literal> is set then idPass authentication
+ (Version 3 only) is used. If none of the options are set, no
+ authentication parameters are set as part of the Initialize Request
+ (obviously).
+ </para>
+ <para>
+ When option <literal>async</literal> is 1, it really means that
+ all network operations are postponed (and queued) until the
+ function <literal>Z3950_event</literal> is invoked. When doing so
+ it doesn't make sense to check for errors after
+ <literal>Z3950_connection_new</literal> is called since that
+ operation "connecting - and init" is still incomplete and the
+ API cannot tell the outcome (yet).
+ </para>
+ </sect2>
</sect1>
<sect1 id="zoom.query"><title>Queries</title>
<para>
sort criteria using the same string notation for sort as offered by
the <link linkend="sortspec">YAZ client</link>.
</para>
+ <sect2><title>Protocol behavior</title>
+ <para>
+ The query object is just an interface for the member Query
+ in the SearchRequest. The sortby-function is an interface to the
+ sortSequence member of the SortRequest.
+ </para>
+ </sect2>
</sect1>
<sect1 id="zoom.resultsets"><title>Result sets</title>
<para>
const char *key,
const char *val);
- int Z3950_resultset_size (Z3950_resultset r);
-
- void *Z3950_resultset_get (Z3950_resultset s, size_t pos,
- const char *type, size_t *len);
+ size_t Z3950_resultset_size (Z3950_resultset r);
</synopsis>
<para>
Function <function>Z3950_resultset_options</function> sets or
The number of hits also called result-count is returned by
function <function>Z3950_resultset_size</function>.
</para>
- <para>
- Function <function>Z3950_resultset_get</function> is similar to
- <link linkend="zoom.record.get">
- <function>Z3950_record_get</function></link> but
- instead of operating on a record object, it operates on a record on
- a given offset within a result set.
- </para>
<table frame="top"><title>ZOOM Result set Options</title>
<tgroup cols="3">
<colspec colwidth="4*" colname="name"></colspec>
value, then target will return all records using small element set name
</entry><entry>0</entry></row>
<row><entry>
- largeSetLowerBound</entry><entry>If hits is greator than this value, the target
- will return no records.
+ largeSetLowerBound</entry><entry>If hits is greator than this
+ value, the target will return no records.
</entry><entry>1</entry></row>
<row><entry>
mediumSetPresentNumber</entry><entry>This value represents
</tbody>
</tgroup>
</table>
+ <sect2>
+ <title>Protocol behavior</title>
+ <para>
+ The creation of a result set involves at least a SearchRequest
+ - SearchResponse protocol handshake. Following that, if a sort
+ critieria was specified as part of the query, a sortRequest -
+ SortResponse handshake takes place. Note that it is necessary to
+ perform sorting before any retrieval takes place, so no records will
+ be returned from the target as part of the SearchResponse because these
+ would be unsorted. Hence, piggyback is disabled when sort critieria
+ is set. Following Search - and a Possible sort, Retrieval takes
+ place - as one or more Present Requests - Present Response being
+ transferred.
+ </para>
+ <para>
+ The API allows for two different modes for retrieval. A high level
+ mode which is somewhat more powerful and a low level one.
+ The low level is "enabled" when the settings
+ <literal>smallSetUpperBound</literal>,
+ <literal>mediumSetPresentNumber</literal> and
+ <literal>largeSetLowerBound</literal> are set. The low level mode
+ thus allows you to precisely set how records are returned as part
+ of a search response as offered by the Z39.50 protocol.
+ Since the client may be retrieving records as part of the
+ search response, this mode doesn't work well if sorting is used.
+ </para>
+ <para>
+ The high-level mode allows you to fetch a range of records from
+ the result set with a given start offset. When you use this mode
+ the client will automatically use piggyback if that is possible
+ with the target and perform one or more present requests as needed.
+ Even if the target returns fewer records as part of a present response
+ because of a record size limit, etc. the client will repeat sending
+ present requests. As an example, if option <literal>start</literal>
+ is 0 (default) and <literal>count</literal> is 4, and
+ <literal>piggyback</literal> is 1 (default) and no sorting critieria
+ is specified, then the client will attempt to retrieve the 4
+ records as part the search response (using piggyback). On the other
+ hand, if either <literal>start</literal> is positive or if
+ a sorting criteria is set, or if <literal>piggyback</literal>
+ is 0, then the client will not perform piggyback but send Present
+ Requests instead.
+ </para>
+ <para>
+ If either of the options <literal>mediumSetElementSetName</literal> and
+ <literal>smallSetElementSetName</literal> are unset, the value
+ of option <literal>elementSetName</literal> is used for piggyback
+ searches. This means that for the high-level mode you only have
+ to specify one elementSetName option rather than three.
+ </para>
+ </sect2>
</sect1>
<sect1 id="zoom.records"><title>Records</title>
<para>
void *Z3950_record_get (Z3950_record rec, const char *type,
size_t *len);
+ Z3950_record Z3950_record_dup (Z3950_record rec);
+
void Z3950_record_destroy (Z3950_record rec);
</synopsis>
<para>
- Records are created by functions
+ References to temporary records are returned by functions
<function>Z3950_resultset_records</function> or
- <function>Z3950_resultset_record</function>
- and destroyed by <function>Z3950_record_destroy</function>.
+ <function>Z3950_resultset_record</function>.
+ </para>
+ <para>
+ If a persistent pointer to a record is desired
+ <function>Z3950_record_dup</function> should be used.
+ It returns a record reference that at any
+ later stage should be destroyed by
+ <function>Z3950_record_destroy</function>.
</para>
<para>
- A single record is created and returned by function
+ A single record is returned by function
<function>Z3950_resultset_record</function> that takes a
position as argument. First record has position zero.
If no record could be obtained <literal>NULL</literal> is returned.
Function <function>Z3950_resultset_records</function> retrieves
a number of records from a result set. Parameter <literal>start</literal>
and <literal>count</literal> specifies the range of records to
- be returned. Upon completion array <literal>recs[0], ..recs[count-1]</literal>
+ be returned. Upon completion array
+ <literal>recs[0], ..recs[count-1]</literal>
holds record objects for the records. The array of records
<literal>recs</literal> should be allocate prior to calling
<function>Z3950_resultset_records</function>. Note that for those
nature (type) of the pointer depends on the <function>type</function>
given. In addition for certain types, the length
<literal>len</literal> passed will be set to the size in bytes of
- the returned information. The types <literal>database</literal>,
- <literal>syntax</literal> and <literal>render</literal> are
- supported. More will be added later.
+ the returned information.
+ <variablelist>
+ <varlistentry><term><literal>database</literal></term>
+ <listitem><para>Database of record is returned
+ as a C null-terminated string. Return type <literal>char *</literal>.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry><term><literal>syntax</literal></term>
+ <listitem><para>The transfer syntax (OID) of the record is returned
+ as a C null-terminated string. Return type <literal>char *</literal>.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry><term><literal>render</literal></term>
+ <listitem><para>The record is returned in a display friendly
+ format. Upon completion buffer is returned
+ (type <literal>char *</literal>) and length is stored in
+ <literal>*len</literal>.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry><term><literal>raw</literal></term>
+ <listitem><para>The record is returned in the internal
+ YAZ specific format. The raw data is returned as type
+ <literal>Z_External *</literal> is just the type for
+ the member <literal>retrievalRecord</literal> in
+ type <literal>NamePlusRecord</literal>.
+ </para></listitem>
+ </varlistentry>
+ </variablelist>
</para>
+ <sect2><title>Protocol behavior</title>
+ <para>
+ The functions <function>Z3950_resultset_record</function> and
+ <function>Z3950_resultset_records</function> inspects the client-side
+ record cache. If the records(s) were not found, i.e. not yet retrieved
+ from, they are fetched using Present Requests.
+ </para>
+ </sect2>
</sect1>
<sect1 id="zoom.options"><title>Options</title>
<para>
- Most &zoom; objects provide a way to specify options to default behaviour.
+ Most &zoom; objects provide a way to specify options to default behavior.
From an implementation point of view a set of options is just like
an associate array / hash array, etc.
</para>
occurred for connection <literal>cs[n-1]</literal>.
When no events are pending for the connections, a value of zero is
returned.
- To make sure all outstanding requests are performed call this function
+ To ensure that all outstanding requests are performed call this function
repeatedly until zero is returned.
</para>
</sect1>
projects / yaz-moved-to-github.git / blobdiff