<!--
### Still to document:
ZOOM_connection_errcode(c)
ZOOM_connection_errmsg(c)
ZOOM_connection_addinfo(c)
ZOOM_connection_addinfo(c)
ZOOM_connection_diagset(c);
ZOOM_diag_str(error)
ZOOM_resultset_record_immediate(s, pos)
ZOOM_resultset_cache_reset(r)
ZOOM_resultset_sort(r, sort_type, sort_spec)
ZOOM_resultset_sort1(r, sort_type, sort_spec)
ZOOM_options_set_callback(opt, function, handle)
ZOOM_options_create_with_parent2(parent1, parent2)
ZOOM_options_getl(opt, name, len)
ZOOM_options_setl(opt, name, value, len)
ZOOM_options_get_bool(opt, name, defa)
ZOOM_options_get_int(opt, name, defa)
ZOOM_options_set_int(opt, name, value)
ZOOM_connection_scan1 (ZOOM_connection c, ZOOM_query startterm)
ZOOM_query_cql2rpn(ZOOM_query s, const char *str, ZOOM_connection conn)
-->
<!-- $Id: zoom.xml,v 1.47 2006/04/24 09:21:35 adam Exp $ -->
 <chapter id="zoom"><title>ZOOM</title>
  <para>
    &zoom; is an acronym for 'Z39.50 Object-Orientation Model' and is
   an initiative started by Mike Taylor (Mike is from the UK, which
   explains the peculiar name of the model). The goal of &zoom; is to
   provide a common Z39.50 client API not bound to a particular
   programming language or toolkit.
  </para>

  <note>
   <para>
    A recent addition to &yaz; is SRW support. You can now make
    SRW ZOOM connections by specifying scheme <literal>http://</literal>
    for the hostname for a connection.
   </para>
  </note>

  <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
   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 further, 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
   <ulink url="&url.zoom;">ZOOM web-site</ulink> for
   more information.
  </para>
  
  <para>
   In order to fully understand this chapter you should read and
   try the example programs <literal>zoomtst1.c</literal>,
   <literal>zoomtst2.c</literal>, .. in the <literal>zoom</literal>
   directory.
  </para>
  
  <para>
   The C language misses features found in object oriented languages
   such as C++, Java, etc. For example, you'll have to manually,
   destroy all objects you create, even though you may think of them as
   temporary. Most objects has a <literal>_create</literal> - and a
   <literal>_destroy</literal> variant.
   All objects are in fact pointers to internal stuff, but you don't see
   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 describes 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.
   </para>
   <synopsis>
    #include &lt;yaz/zoom.h>
    
    ZOOM_connection ZOOM_connection_new (const char *host, int portnum);
    
    ZOOM_connection ZOOM_connection_create (ZOOM_options options);
    
    void ZOOM_connection_connect(ZOOM_connection c, const char *host,
                                 int portnum);
    void ZOOM_connection_destroy (ZOOM_connection c);
   </synopsis>
   <para>
    Connection objects are created with either function
    <function>ZOOM_connection_new</function> or 
    <function>ZOOM_connection_create</function>.
    The former creates and automatically attempts to establish a network
    connection with the target. The latter doesn't establish
    a connection immediately, thus allowing you to specify options
    before establishing network connection using the function
    <function>ZOOM_connection_connect</function>. 
    If the port number, <literal>portnum</literal>, is zero, the
    <literal>host</literal> is consulted for a port specification.
    If no port is given, 210 is used. A colon denotes the beginning of
    a port number in the host string. If the host string includes a
    slash, the following part specifies a database for the connection.
   </para>
   <para>
    You can prefix the host with a scheme followed by colon. The
    default scheme is <literal>tcp</literal> (Z39.50 protocol).
    The scheme <literal>http</literal> selects SRW over HTTP.
   </para>
   <para>
    You can prefix the scheme-qualified host-string with one or more
    comma-separated
    <literal><parameter>key</parameter>=<parameter>value</parameter></literal>
    sequences, each of which represents an option to be set into the
    connection structure <emphasis>before</emphasis> the
    protocol-level connection is forged and the initialisation
    handshake takes place.  This facility can be used to provide
    authentication credentials, as in host-strings such as:
    <literal>user=admin,password=halfAm4n,tcp:localhost:8017/db</literal>
   </para>
   <para>
    Connection objects should be destroyed using the function
    <function>ZOOM_connection_destroy</function>.
   </para>
   <synopsis>
    void ZOOM_connection_option_set(ZOOM_connection c,
                                    const char *key, const char *val);

    void ZOOM_connection_option_setl(ZOOM_connection c,
                                     const char *key,
                                     const char *val, int len);

    const char *ZOOM_connection_option_get(ZOOM_connection c,
                                           const char *key);
    const char *ZOOM_connection_option_getl(ZOOM_connection c,
                                            const char *key,
                                            int *lenp);
   </synopsis>
   <para>
    The functions <function>ZOOM_connection_option_set</function> and
    <function>ZOOM_connection_option_setl</function> allows you to
    set an option given by <parameter>key</parameter> to the value
    <parameter>value</parameter> for the connection. 
    For <function>ZOOM_connection_option_set</function>, the
    value is assumed to be a 0-terminated string. Function
    <function>ZOOM_connection_option_setl</function> specifies a
    value of a certain size (len).
   </para>
   <para>
    Functions <function>ZOOM_connection_option_get</function> and
    <function>ZOOM_connection_option_getl</function> returns
    the value for an option given by <parameter>key</parameter>.
   </para>
   <table frame="top"><title>ZOOM Connection Options</title>
    <tgroup cols="3">
     <colspec colwidth="4*" colname="name"></colspec>
     <colspec colwidth="7*" colname="description"></colspec>
     <colspec colwidth="3*" colname="default"></colspec>
     <thead>
      <row>
       <entry>Option</entry>
       <entry>Description</entry>
       <entry>Default</entry>
      </row>
     </thead>
     <tbody>
      <row><entry>
        implementationName</entry><entry>Name of Your client
       </entry><entry>none</entry></row>
      <row><entry>
        user</entry><entry>Authentication user name
       </entry><entry>none</entry></row>
      <row><entry>
        group</entry><entry>Authentication group name
       </entry><entry>none</entry></row>
      <row><entry>
        password</entry><entry>Authentication password.
       </entry><entry>none</entry></row>
      <row><entry>
        host</entry><entry>Target host. This setting is "read-only".
        It's automatically set internally when connecting to a target.
       </entry><entry>none</entry></row>
      <row><entry>
        proxy</entry><entry>Proxy host
       </entry><entry>none</entry></row>
      <row><entry>
        async</entry><entry>If true (1) the connection operates in 
        asynchronous operation which means that all calls are non-blocking
        except
        <link linkend="zoom.events"><function>ZOOM_event</function></link>.
       </entry><entry>0</entry></row>
      <row><entry>
        maximumRecordSize</entry><entry> Maximum size of single record.
       </entry><entry>1 MB</entry></row>
      <row><entry>
        preferredMessageSize</entry><entry> Maximum size of multiple records.
       </entry><entry>1 MB</entry></row>
      <row><entry>
        lang</entry><entry> Language for negotiation.
       </entry><entry>none</entry></row>
      <row><entry>
        charset</entry><entry> Character set for negotiation.
       </entry><entry>none</entry></row>
      <row><entry>
        serverImplementationId</entry><entry>
	Implementation ID of server.  (The old targetImplementationId
	option is also supported for the benefit of old applications.)
       </entry><entry>none</entry></row>
      <row><entry>
        targetImplementationName</entry><entry>
	Implementation Name of server.  (The old
	targetImplementationName option is also supported for the
	benefit of old applications.)
       </entry><entry>none</entry></row>
      <row><entry>
        serverImplementationVersion</entry><entry>
	Implementation Version of server.  (the old
	targetImplementationVersion option is also supported for the
	benefit of old applications.)
       </entry><entry>none</entry></row>
      <row><entry>
        databaseName</entry><entry>One or more database names
        separated by character plus (<literal>+</literal>), which to
        be used by subsequent search requests on this Connection.
       </entry><entry>Default</entry></row>
      <row><entry>
        piggyback</entry><entry>True (1) if piggyback should be
        used in searches; false (0) if not.
       </entry><entry>1</entry></row>
      <row><entry>
        smallSetUpperBound</entry><entry>If hits is less than or equal to this
        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 greater than this
        value, the target will return no records.
       </entry><entry>1</entry></row>
      <row><entry>
        mediumSetPresentNumber</entry><entry>This value represents
        the number of records to be returned as part of a search when when
        hits is less than or equal to large set lower bound and if hits
        is greater than small set upper bound.
       </entry><entry>0</entry></row>
      <row><entry>
        smallSetElementSetName</entry><entry>
        The element set name to be used for small result sets.
       </entry><entry>none</entry></row>
      <row><entry>
        mediumSetElementSetName</entry><entry>
        The element set name to be for medium-sized result sets.
       </entry><entry>none</entry></row>
     </tbody>
    </tgroup>
   </table>
   <para>
    If either option <literal>lang</literal> or <literal>charset</literal>
    is set, then 
    <ulink url="&url.z39.50.charneg;">
     Character Set and Language Negotiation</ulink> is in effect.
   </para>
   <synopsis>
     int ZOOM_connection_error (ZOOM_connection c, const char **cp,
                                const char **addinfo);
     int ZOOM_connection_error_x (ZOOM_connection c, const char **cp,
                                  const char **addinfo, const char **dset);
   </synopsis>
   <para>
    Function <function>ZOOM_connection_error</function> checks for
    errors for the last operation(s) performed. The function returns
    zero if no errors occurred; non-zero otherwise indicating the error.
    Pointers <parameter>cp</parameter> and <parameter>addinfo</parameter>
    holds messages for the error and additional-info if passed as
    non-<literal>NULL</literal>. Function
    <function>ZOOM_connection_error_x</function> is an extended version
    of <function>ZOOM_connection_error</function> that is capable of
    returning name of diagnostic set in <parameter>dset</parameter>.
   </para>
   <sect2><title>Z39.50 Protocol behavior</title>
    <para>
     The calls <function>ZOOM_connection_new</function> and
     <function>ZOOM_connection_connect</function> establishes 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>ZOOM_event</literal> is invoked. When doing so
     it doesn't make sense to check for errors after
     <literal>ZOOM_connection_new</literal> is called since that
     operation "connecting - and init" is still incomplete and the
     API cannot tell the outcome (yet).
    </para>
    </sect2>
   <sect2><title>SRW Protocol behavior</title>
    <para>
     The SRW protocol doesn't feature an Inititialize Request, so
     the connection phase merely establishes a TCP/IP connection
     with the SOAP service.
    </para>
    <para>Most of the ZOOM connection options do not
     affect SRW and they are ignored. However, future versions
     of &yaz; might honor <literal>implementationName</literal> and
     put that as part of User-Agent header for HTTP requests.
     </para>
    <para>
     The <literal>charset</literal> is used in the Content-Type header
     of HTTP requests.
    </para>
   </sect2>
  </sect1>
  <sect1 id="zoom.query"><title>Queries</title>
   <para>
    Query objects represents queries.
   </para>
   <synopsis>
     ZOOM_query ZOOM_query_create(void);

     void ZOOM_query_destroy(ZOOM_query q);

     int ZOOM_query_prefix(ZOOM_query q, const char *str);

     int ZOOM_query_cql(ZOOM_query s, const char *str);

     int ZOOM_query_sortby(ZOOM_query q, const char *criteria);
   </synopsis>
   <para>
    Create query objects using <function>ZOOM_query_create</function>
    and destroy them by calling <function>ZOOM_query_destroy</function>.
    RPN-queries can be specified in <link linkend="PQF">PQF</link>
    notation by using the
    function <function>ZOOM_query_prefix</function>.
    The <function>ZOOM_query_cql</function> specifies a CQL
    query to be sent to the server/target.
    More query types will be added in future versions of &yaz;, such as
    <link linkend="CCL">CCL</link> to RPN-mapping, native CCL query,
    etc. In addition to a search, a sort criteria may be set. Function
    <function>ZOOM_query_sortby</function> specifies a 
    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>
    The result set object is a container for records returned from
    a target.
   </para>
   <synopsis>
     ZOOM_resultset ZOOM_connection_search(ZOOM_connection,
                                           ZOOM_query q);

     ZOOM_resultset ZOOM_connection_search_pqf(ZOOM_connection c,
                                               const char *q);

     void ZOOM_resultset_destroy(ZOOM_resultset r);
   </synopsis>
   <para>
    Function <function>ZOOM_connection_search</function> creates
     a result set given a connection and query.
    Destroy a result set by calling
    <function>ZOOM_resultset_destroy</function>.
    Simple clients may using PQF only may use function
    <function>ZOOM_connection_search_pqf</function> in which case
    creating query objects is not necessary.
   </para>
   <synopsis>
     void ZOOM_resultset_option_set (ZOOM_resultset r,
                                      const char *key,
                                      const char *val);

     const char *ZOOM_resultset_option_get (ZOOM_resultset r,
                                             const char *key);

     size_t ZOOM_resultset_size (ZOOM_resultset r);
   </synopsis>
   <para>
    Functions <function>ZOOM_resultset_options_set</function> and
    <function>ZOOM_resultset_get</function> sets and gets an option
    for a result set similar to <function>ZOOM_connection_option_get</function>
    and <function>ZOOM_connection_option_set</function>.
   </para>
   <para>
    The number of hits also called result-count is returned by
    function <function>ZOOM_resultset_size</function>.
   </para>
   <table frame="top"><title>ZOOM Result set Options</title>
    <tgroup cols="3">
     <colspec colwidth="4*" colname="name"></colspec>
     <colspec colwidth="7*" colname="description"></colspec>
     <colspec colwidth="2*" colname="default"></colspec>
     <thead>
      <row>
       <entry>Option</entry>
       <entry>Description</entry>
       <entry>Default</entry>
      </row>
     </thead>
     <tbody>
      <row><entry>
        start</entry><entry>Offset of first record to be 
        retrieved from target. First record has offset 0 unlike the
        protocol specifications where first record has position 1.
       </entry><entry>0</entry></row>
      <row><entry>
        count</entry><entry>Number of records to be retrieved.
       </entry><entry>0</entry></row>
      <row><entry>
	presentChunk</entry><entry>The number of records to be
	requested from the server in each chunk (present requst).  The
	value 0 means to request all the records in a single chunk.
	(The old <literal>step</literal>
	option is also supported for the benefit of old applications.)
       </entry><entry>0</entry></row>
      <row><entry>
        elementSetName</entry><entry>Element-Set name of records. 
        Most targets should honor element set name <literal>B</literal>
        and <literal>F</literal> for brief and full respectively.
       </entry><entry>none</entry></row>
      <row><entry>
        preferredRecordSyntax</entry><entry>Preferred Syntax, such as
        <literal>USMARC</literal>, <literal>SUTRS</literal>, etc.
       </entry><entry>none</entry></row>
      <row><entry>
        schema</entry><entry>Schema for retrieval, such as
        <literal>Gils-schema</literal>, <literal>Geo-schema</literal>, etc.
       </entry><entry>none</entry></row>
      <row><entry>
        setname</entry><entry>Name of Result Set (Result Set ID).
        If this option isn't set, the ZOOM module will automatically
        allocate a result set name.
       </entry><entry>default</entry></row>
     </tbody>
    </tgroup>
   </table>
   <para>
    For servers that support Search Info report, the following
    options may be read using <function>ZOOM_resultset_get</function>.
    This detailed information is read after a successful search has
    completed.
   </para>
   <para>
    This information is a list of of items, where each item is
    information about a term or subquery. All items in the list 
    are prefixed by 
    <literal>SearchResult.</literal><replaceable>no</replaceable>
    where no presents the item number (0=first, 1=second). 
    Read <literal>searchresult.size</literal> to determine the
    number of items.
   </para>
   <table frame="top"><title>Search Info Report options</title>
    <tgroup cols="2">
     <colspec colwidth="4*" colname="name"></colspec>
     <colspec colwidth="7*" colname="description"></colspec>
     <thead>
      <row>
       <entry>Option</entry>
       <entry>Description</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>searchresult.size</entry>
       <entry>
	number of search result entries. This option is-nonexistant
	if no entries are returned by the server.
       </entry>
      </row>
      <row>
       <entry>searchresult.<replaceable>no</replaceable>.id</entry>
       <entry>sub query ID</entry>
      </row>
      <row>
       <entry>searchresult.<replaceable>no</replaceable>.count</entry>
       <entry>result count for item (number of hits)</entry>
      </row>
      <row>
       <entry>searchresult.<replaceable>no</replaceable>.subquery.term</entry>
       <entry>subquery term</entry>
      </row>
      <row>
       <entry>
	searchresult.<replaceable>no</replaceable>.interpretation.term
       </entry>
       <entry>interpretation term</entry>
      </row>
      <row>
       <entry>
	searchresult.<replaceable>no</replaceable>.recommendation.term
       </entry>
       <entry>recommendation term</entry>
      </row>
     </tbody>
    </tgroup>
   </table>
   <sect2>
    <title>Z39.50 Protocol behavior</title>
    <para>
     The creation of a result set involves at least a SearchRequest
     - SearchResponse protocol handshake. Following that, if a sort
     criteria 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 criteria
     are set. Following Search - and a possible sort - Retrieval takes
     place - as one or more Present Requests/Response pairs 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 searching on a Connection object
     for which 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 criteria
     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>
   <sect2>
    <title>SRW Protocol behavior</title>
    <para>
     Current version of &yaz; does not take advantage of a result set id
     returned by the SRW server. Future versions might do, however.
     Since, the ZOOM driver does not save result set IDs any
     present (retrieval) is transformed to a SRW SearchRetrieveRequest
     with same query but, possibly, different offsets.
    </para>
    <para>
     Option <literal>schema</literal> specifies SRW schema
     for retrieval. However, options <literal>elementSetName</literal> and
     <literal>preferredRecordSyntax</literal> are ignored.
    </para>
    <para>
     Options <literal>start</literal> and <literal>count</literal> 
     are supported by SRW.
     The remaining options
     <literal>piggyback</literal>, 
     <literal>smallSetUpperBound</literal>, 
     <literal>largeSetLowerBound</literal>, 
     <literal>mediumSetPresentNumber</literal>, 
     <literal>mediumSetElementSetName</literal>,
      <literal>smallSetElementSetName</literal> are
     unsupported.
    </para>
    <para>
     SRW supports CQL queries, <emphasis>not</emphasis> PQF.
     If PQF is used, however, the PQF query is transferred anyway
     using non-standard element <literal>pQuery</literal> in
     SRW SearchRetrieveRequest.
    </para>
    <para>
     Unfortunately, SRW does not define a database setting. Hence,
     <literal>databaseName</literal> is unsupported and ignored.
     However, the path part in host parameter for functions 
     <function>ZOOM_connecton_new</function> and
     <function>ZOOM_connection_connect</function> acts as a
     database (at least for the &yaz; SRW server).
    </para>
   </sect2>
  </sect1>
  <sect1 id="zoom.records"><title>Records</title>
   <para>
    A record object is a retrieval record on the client side -
    created from result sets.
   </para>
   <synopsis>
     void ZOOM_resultset_records (ZOOM_resultset r,
                                  ZOOM_record *recs,
                                  size_t start, size_t count);
     ZOOM_record ZOOM_resultset_record (ZOOM_resultset s, size_t pos);

     const char *ZOOM_record_get (ZOOM_record rec, const char *type,
                                  size_t *len);

     ZOOM_record ZOOM_record_clone (ZOOM_record rec);

     void ZOOM_record_destroy (ZOOM_record rec);
   </synopsis>
   <para>
    References to temporary records are returned by functions 
    <function>ZOOM_resultset_records</function> or
    <function>ZOOM_resultset_record</function>.
    </para>
   <para>
    If a persistent reference to a record is desired
    <function>ZOOM_record_clone</function> should be used.
    It returns a record reference that should be destroyed
    by a call to <function>ZOOM_record_destroy</function>.
   </para>
   <para>
    A single record is returned by function
    <function>ZOOM_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.
   </para>
   <para>
    Function <function>ZOOM_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>
    holds record objects for the records. The array of records
     <literal>recs</literal> should be allocated prior the call
    <function>ZOOM_resultset_records</function>. Note that for those
    records that couldn't be retrieved from the target
    <literal>recs[ ..]</literal> is set to <literal>NULL</literal>.
   </para>
   <para id="zoom.record.get">
    In order to extract information about a single record,
    <function>ZOOM_record_get</function> is provided. The
    function returns a pointer to certain record information. The
    nature (type) of the pointer depends on the parameter,
    <parameter>type</parameter>.
   </para>
   <para>
    The <parameter>type</parameter> is a string of the format:
   </para>
   <para>
    <replaceable>form</replaceable>[; charset=<replaceable>from</replaceable>[,<replaceable>to</replaceable>]]
   </para>
   <para>
    where <replaceable>form</replaceable> specifies the format of the
    returned record, <replaceable>from</replaceable>
    specifies the character set of the record in its original form
    (as returned by the server), <replaceable>to</replaceable> specifies
    the output (returned)
    character set encoding.
    If charset is not given, then no character set conversion takes place.
    If <replaceable>to</replaceable> is omitted UTF-8 is assumed.
   </para>
   <para>
    In addition, for certain types, the length
    <literal>len</literal> passed will be set to the size in bytes of
    the returned information. 
    </para>
   <para>
    The following are the supported values for <replaceable>form</replaceable>.
    <variablelist>
     <varlistentry><term><literal>database</literal></term>
      <listitem><para>Database of record is returned
        as a C null-terminated string. Return type
        <literal>const char *</literal>. 
       </para></listitem>
     </varlistentry>
     <varlistentry><term><literal>syntax</literal></term>
      <listitem><para>The transfer syntax of the record is returned
        as a C null-terminated string containing the symbolic name of
	the record syntax, e.g. <literal>Usmarc</literal>. Return type
	is
        <literal>const 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>const 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. For GRS-1, Explain, and others, the
        raw data is returned as type 
        <literal>Z_External *</literal> which is just the type for
        the member <literal>retrievalRecord</literal> in
        type <literal>NamePlusRecord</literal>.
        For SUTRS and octet aligned record (including all MARCs) the
        octet buffer is returned and the length of the buffer.
       </para></listitem>
     </varlistentry>
     <varlistentry><term><literal>xml</literal></term>
      <listitem><para>The record is returned in XML if possible.
	SRW/SRU and Z39.50 records with transfer syntax XML are
	returned verbatim. MARC records are returned in
	<ulink url="&url.marcxml;">
	 MARCXML
	 </ulink> 
	(converted from ISO2709 to MARCXML by YAZ).
	GRS-1 and OPAC records are not supported for this form.
        Upon completion, the XML buffer is returned
	(type <literal>const char *</literal>) and length is stored in
        <literal>*len</literal>.
       </para></listitem>
     </varlistentry>
     <varlistentry><term><literal>opac</literal></term>
      <listitem><para>OPAC for record is returned in XML.
       </para></listitem>
     </varlistentry>
    </variablelist>
   </para>
   <para>
    Most
    <ulink url="&url.marc21;">MARC21</ulink>
    records uses the 
    <ulink url="&url.marc8;">MARC-8</ulink>
    character set encoding.
    An application that wishes to display in Latin-1 would use
    <screen>
     render; charset=marc8,iso-8859-1
    </screen>
   </para>
   <sect2><title>Z39.50 Protocol behavior</title>
    <para>
     The functions <function>ZOOM_resultset_record</function> and
     <function>ZOOM_resultset_records</function> inspects the client-side
     record cache. Records not found in cache are fetched using
     Present.
     The functions may block (and perform network I/O)  - even though option
     <literal>async</literal> is 1, because they return records objects.
     (and there's no way to return records objects without retrieving them!).
     </para>
    <para>
     There is a trick, however, in the usage of function
     <function>ZOOM_resultset_records</function> that allows for
     delayed retrieval (and makes it non-blocking). By using
     a null pointer for <parameter>recs</parameter> you're indicating
     you're not interested in getting records objects
     <emphasis>now</emphasis>.
    </para>
   </sect2>
   <sect2><title>SRW Protocol behavior</title>
    <para>
     The ZOOM driver for SRW treats records returned by a SRW server
     as if they where Z39.50 records with transfer syntax XML and
     no element set name or database name.
    </para>
   </sect2>
  </sect1>
  <sect1 id="zoom.scan"><title>Scan</title>
   <para>
    This section describes an interface for Scan. Scan is not an
    official part of the ZOOM model yet. The result of a scan operation
    is the <literal>ZOOM_scanset</literal> which is a set of terms
    returned by a target.
   </para>

   <para>
    The Scan interface is Z39.50 only. SRW version 1.0 does not
    support this.
   </para>

   <synopsis>
    ZOOM_scanset ZOOM_connection_scan(ZOOM_connection c,
                                      const char *startpqf);

    size_t ZOOM_scanset_size(ZOOM_scanset scan);

    const char * ZOOM_scanset_term(ZOOM_scanset scan, size_t pos,
                                   int *occ, size_t *len);

    const char * ZOOM_scanset_display_term(ZOOM_scanset scan, size_t pos,
                                           int *occ, size_t *len);

    void ZOOM_scanset_destroy (ZOOM_scanset scan);

    const char *ZOOM_scanset_option_get(ZOOM_scanset scan,
                                         const char *key);

    void ZOOM_scanset_option_set(ZOOM_scanset scan, const char *key,
                                 const char *val);
    </synopsis>
   <para>
    The scan set is created by function
    <function>ZOOM_connection_scan</function> which performs a scan
    operation on the connection using the specified
    <parameter>startpqf</parameter>.
    If the operation was successful, the size of the scan set can be
    retrieved by a call to <function>ZOOM_scanset_size</function>.
    Like result sets, the items are numbered 0,..size-1.
    To obtain information about a particular scan term, call function
    <function>ZOOM_scanset_term</function>. This function takes
    a scan set offset <literal>pos</literal> and returns a pointer
    to a <emphasis>raw term</emphasis> or <literal>NULL</literal> if
    non-present.
    If present, the <literal>occ</literal> and <literal>len</literal> 
    are set to the number of occurrences and the length
    of the actual term respectively.
    <function>ZOOM_scanset_display_term</function> is similar to
    <function>ZOOM_scanset_term</function> except that it returns
    the <emphasis>display term</emphasis> rather than the raw term.
    In a few cases, the term is different from display term. Always
    use the display term for display and the raw term for subsequent
    scan operations (to get more terms, next scan result, etc).
   </para>
   <para>
    A scan set may be freed by a call to function
    <function>ZOOM_scanset_destroy</function>.
    Functions <function>ZOOM_scanset_option_get</function> and
    <function>ZOOM_scanset_option_set</function> retrieves and sets
    an option respectively.
   </para>

   <para>
    The <parameter>startpqf</parameter> is a subset of PQF, namely
    the Attributes+Term part. Multiple <literal>@attr</literal> can
    be used. For example to scan in title (complete) phrases:
    <literallayout>
     @attr 1=4 @attr 6=2 "science o"
    </literallayout>
   </para>
   
   <table frame="top"><title>ZOOM Scan Set Options</title>
    <tgroup cols="3">
     <colspec colwidth="4*" colname="name"></colspec>
     <colspec colwidth="7*" colname="description"></colspec>
     <colspec colwidth="2*" colname="default"></colspec>
     <thead>
      <row>
       <entry>Option</entry>
       <entry>Description</entry>
       <entry>Default</entry>
      </row>
     </thead>
     <tbody>
      <row><entry>
        number</entry><entry>Number of Scan Terms requested in next scan.
        After scan it holds the actual number of terms returned.
       </entry><entry>10</entry></row>
      <row><entry>
        position</entry><entry>Preferred Position of term in response
        in next scan; actual position after completion of scan.
       </entry><entry>1</entry></row>
      <row><entry>
        stepSize</entry><entry>Step Size
       </entry><entry>0</entry></row>
      <row><entry>
        scanStatus</entry><entry>An integer indicating the Scan Status
        of last scan.
       </entry><entry>0</entry></row>
     </tbody>
    </tgroup>
   </table>
  </sect1>

  <sect1 id="zoom.ext"><title>Extended Services</title>
   <para>
    ZOOM offers an interface to a subset of the Z39.50 extended services
    as well as a few privately defined ones:
   </para>
   <itemizedlist>
    <listitem>
     <para>
      Z39.50 Item Order (ILL).
      See <xref linkend="zoom.ext.itemorder"/>.
     </para>
    </listitem>
    <listitem>
     <para>
      Record Update. This allows a client to insert, modify or delete
      records.
      See <xref linkend="zoom.ext.update"/>.
     </para>
    </listitem>
    <listitem>
     <para>
      Database Create. This a non-standard feature. Allows a client
      to create a database.
      See <xref linkend="zoom.ext.dbcreate"/>.
     </para>
    </listitem>
    <listitem>
     <para>
      Database Drop. This a non-standard feature. Allows a client
      to delete/drop a database.
      See <xref linkend="zoom.ext.dbdrop"/>.
     </para>
     </listitem>
    <listitem>
     <para>
      Commit operation. This a non-standard feature. Allows a client
      to commit operations.
      See <xref linkend="zoom.ext.commit"/>.
     </para>
    </listitem>
    <!-- all the ILL PDU options should go here too -->
   </itemizedlist>
   <para>
    To create an extended service operation a <literal>ZOOM_package</literal>
    must be created. The operation is a five step operation. The
    package is created, package is configured by means of options,
    the package is send, result is inspected (by means of options),
    the package is destroyed.
   </para>
   <synopsis>
    ZOOM_package ZOOM_connection_package(ZOOM_connection c,
                                         ZOOM_options options);

    const char *ZOOM_package_option_get(ZOOM_package p,
                                        const char *key);
    void ZOOM_package_option_set(ZOOM_package p, const char *key,
                                 const char *val);
    void ZOOM_package_send(ZOOM_package p, const char *type);

    void ZOOM_package_destroy(ZOOM_package p);
   </synopsis>
   <para>
    The <function>ZOOM_connection_package</function> creates a
    package for the connection given using the options specified.
   </para>
   <para>
    Functions <function>ZOOM_package_option_get</function> and
    <function>ZOOM_package_option_set</function> gets and sets
    options.
   </para>
   <para>
    <function>ZOOM_package_send</function> sends
    the package the via connection specified in 
    <function>ZOOM_connection_package</function>.
    The <parameter>type</parameter> specifies the actual extended service
    package type to be sent.
   </para>

   <table frame="top"><title>Extended Service Common Options</title>
    <tgroup cols="3">
     <colspec colwidth="4*" colname="name"></colspec>
     <colspec colwidth="7*" colname="description"></colspec>
     <colspec colwidth="3*" colname="default"></colspec>
     <thead>
      <row>
       <entry>Option</entry>
       <entry>Description</entry>
       <entry>Default</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>package-name</entry>
       <entry>Extended Service Request package name. Must be specified
       as part of a request</entry>
       <entry>none</entry>
      </row>
      <row>
       <entry>user-id</entry>
       <entry>User ID of Extended Service Package. Is a request option</entry>
       <entry>none</entry>
      </row>
      <row>
       <entry>function</entry>
       <entry>
	Function of package - one of <literal>create</literal>,
	<literal>delete</literal>, <literal>modify</literal>. Is
	a request option.
       </entry>
       <entry><literal>create</literal></entry>
      </row>
      <row>
       <entry>targetReference</entry>
       <entry>
	Target Reference. This is part of the response as returned
	by the server. Read it after a succesful operation.
       </entry>
       <entry><literal>none</literal></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <sect2 id="zoom.ext.itemorder"><title>Item Order</title>
    <para>
     For Item Order, type must be set to <literal>itemorder</literal> in
     <function>ZOOM_package_send</function>.
    </para>

    <table frame="top"><title>Item Order Options</title>
     <tgroup cols="3">
      <colspec colwidth="4*" colname="name"></colspec>
      <colspec colwidth="7*" colname="description"></colspec>
      <colspec colwidth="3*" colname="default"></colspec>
      <thead>
       <row>
	<entry>Option</entry>
	<entry>Description</entry>
	<entry>Default</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry>contact-name</entry>
	<entry>ILL contact name</entry>
	<entry>none</entry>
       </row>
       <row>
	<entry>contact-phone</entry>
	<entry>ILL contact phone</entry>
	<entry>none</entry>
       </row>
       <row>
	<entry>contact-email</entry>
	<entry>ILL contact email</entry>
	<entry>none</entry>
       </row>
       <row>
	<entry>itemorder-item</entry>
	<entry>Position for item (record) requested. An integer</entry>
	<entry>1</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   </sect2>

   <sect2 id="zoom.ext.update"><title>Record Update</title>
    <para>
     For Record Update, type must be set to <literal>update</literal> in
     <function>ZOOM_package_send</function>.
    </para>

    <table frame="top"><title>Record Update Options</title>
     <tgroup cols="3">
      <colspec colwidth="4*" colname="name"></colspec>
      <colspec colwidth="7*" colname="description"></colspec>
      <colspec colwidth="3*" colname="default"></colspec>
      <thead>
       <row>
	<entry>Option</entry>
	<entry>Description</entry>
	<entry>Default</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry>action</entry>
	<entry>
	 The update action. One of 
	 <literal>specialUpdate</literal>,
	 <literal>recordInsert</literal>,
	 <literal>recordReplace</literal>,
	 <literal>recordDelete</literal>,
	 <literal>elementUpdate</literal>.
	</entry>
	<entry><literal>specialUpdate</literal></entry>
       </row>
       <row>
	<entry>recordIdOpaque</entry>
	<entry>Opaque Record ID</entry>
	<entry>none</entry>
       </row>
       <row>
	<entry>recordIdNumber</entry>
	<entry>Record ID number</entry>
	<entry>none</entry>
       </row>
       <row>
	<entry>record</entry>
	<entry>The record itself</entry>
	<entry>none</entry>
       </row>
       <row>
	<entry>syntax</entry>
	<entry>The record syntax (transfer syntax). Is a string that
	 is a known record syntax.
	</entry>
	<entry>no syntax</entry>
       </row>
       <row>
	<entry>databaseName</entry>
	<entry>Database from connection object</entry>
	<entry>Default</entry>
       </row>
      </tbody>
     </tgroup>
    </table>
    
   </sect2>

   <sect2 id="zoom.ext.dbcreate"><title>Database Create</title>
    <para>
     For Database Create, type must be set to <literal>create</literal> in
     <function>ZOOM_package_send</function>.
    </para>
    
    <table frame="top"><title>Database Create Options</title>
     <tgroup cols="3">
      <colspec colwidth="4*" colname="name"></colspec>
      <colspec colwidth="7*" colname="description"></colspec>
      <colspec colwidth="3*" colname="default"></colspec>
      <thead>
       <row>
	<entry>Option</entry>
	<entry>Description</entry>
	<entry>Default</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry>databaseName</entry>
	<entry>Database from connection object</entry>
	<entry>Default</entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </sect2>
   
   <sect2 id="zoom.ext.dbdrop"><title>Database Drop</title>
    <para>
     For Database Drop, type must be set to <literal>drop</literal> in
     <function>ZOOM_package_send</function>.
    </para>
    
    <table frame="top"><title>Database Create Options</title>
     <tgroup cols="3">
      <colspec colwidth="4*" colname="name"></colspec>
      <colspec colwidth="7*" colname="description"></colspec>
      <colspec colwidth="3*" colname="default"></colspec>
      <thead>
       <row>
	<entry>Option</entry>
	<entry>Description</entry>
	<entry>Default</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry>databaseName</entry>
	<entry>Database from connection object</entry>
	<entry>Default</entry>
       </row>
      </tbody>
     </tgroup>
    </table>
   </sect2>
   
   <sect2 id="zoom.ext.commit"><title>Commit Operation</title>
    <para>
     For Commit, type must be set to <literal>commit</literal> in
     <function>ZOOM_package_send</function>.
    </para>
   </sect2>

   <sect2><title>Protocol behavior</title>
    <para>
     All the extended services are Z39.50-only.
    </para>
    <note>
     <para>
      The database create, drop and commit services are privately defined
      operations.
      Refer to <filename>esadmin.asn</filename> in YAZ for the ASN.1
      definitions.
     </para>
    </note>
   </sect2>
  </sect1>

  <sect1 id="zoom.options"><title>Options</title>
   <para>
    Most &zoom; objects provide a way to specify options to change behavior.
    From an implementation point of view a set of options is just like
    an associative array / hash.
   </para>
   <synopsis>
     ZOOM_options ZOOM_options_create (void);

     ZOOM_options ZOOM_options_create_with_parent (ZOOM_options parent);

     void ZOOM_options_destroy (ZOOM_options opt);
   </synopsis>
   <synopsis>
     const char *ZOOM_options_get (ZOOM_options opt, const char *name);

     void ZOOM_options_set (ZOOM_options opt, const char *name,
                            const char *v);
   </synopsis>
   <synopsis>
     typedef const char *(*ZOOM_options_callback)
                                     (void *handle, const char *name);

     ZOOM_options_callback
             ZOOM_options_set_callback (ZOOM_options opt,
                                        ZOOM_options_callback c,
                                        void *handle);
   </synopsis>
  </sect1>
  <sect1 id="zoom.events"><title>Events</title>
   <para>
    If you're developing non-blocking applications, you have to deal 
    with events.
   </para>
   <synopsis>
    int ZOOM_event (int no, ZOOM_connection *cs);
   </synopsis>
   <para>
    The <function>ZOOM_event</function> executes pending events for
    a number of connections. Supply the number of connections in
    <literal>no</literal> and an array of connections in
    <literal>cs</literal> (<literal>cs[0] ... cs[no-1]</literal>).
    A pending event could be a sending a search, receiving a response,
    etc.
    When an event has occurred for one of the connections, this function
    returns a positive integer <literal>n</literal> denoting that an event
    occurred for connection <literal>cs[n-1]</literal>.
    When no events are pending for the connections, a value of zero is
    returned.
    To ensure that all outstanding requests are performed call this function
    repeatedly until zero is returned.
   </para>
   <para>
    If <function>ZOOM_event</function> returns and returns non-zero, the
    last event that occurred can be expected.
   </para>
   <synopsis>
    int ZOOM_connection_last_event(ZOOM_connection cs);
   </synopsis>
   <para>
    <function>ZOOM_connection_last_event</function> returns an event type
    (integer) for the last event.
   </para>

   <table frame="top"><title>ZOOM Event IDs</title>
    <tgroup cols="2">
     <colspec colwidth="4*" colname="name"></colspec>
     <colspec colwidth="7*" colname="description"></colspec>
     <thead>
      <row>
       <entry>Event</entry>
       <entry>Description</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>ZOOM_EVENT_NONE</entry>
       <entry>No event has occurred</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_CONNECT</entry>
       <entry>TCP/IP connect has initiated</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_SEND_DATA</entry>
       <entry>Data has been transmitted (sending)</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_RECV_DATA</entry>
       <entry>Data has been received)</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_TIMEOUT</entry>
       <entry>Timeout</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_UNKNOWN</entry>
       <entry>Unknown event</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_SEND_APDU</entry>
       <entry>An APDU has been transmitted (sending)</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_RECV_APDU</entry>
       <entry>An APDU has been received</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_RECV_RECORD</entry>
       <entry>A result-set record has been received</entry>
      </row>
      <row>
       <entry>ZOOM_EVENT_RECV_SEARCH</entry>
       <entry>A search result been received</entry>
      </row>
     </tbody>
    </tgroup>
   </table>
  </sect1>
 </chapter>
 
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