-# $Id: ZOOM.pod,v 1.3 2005-11-15 17:33:04 mike Exp $
+# $Id: ZOOM.pod,v 1.10 2005-11-18 17:55:08 mike Exp $
use strict;
use warnings;
=head1 DESCRIPTION
This module provides a nice, Perlish implementation of the ZOOM
-Abstract API described at http://zoom.z3950.org/api/
+Abstract API described and documented at http://zoom.z3950.org/api/
the ZOOM module is implemented as a set of thin classes on top of the
non-OO functions provided by this distribution's C<Net::Z3950::ZOOM>
and
C<ZOOM::Query::PQF>.
Many useful ZOOM applications can be built using only the Connection,
-ResultSet and Record classes, as in the example code-snippet above.
+ResultSet, Record and Exception classes, as in the example
+code-snippet above.
A typical application will begin by creating an Connection object,
then using that to execute searches that yield ResultSet objects, then
fetching records from the result-sets to yield Record objects. If an
error occurs, an Exception object is thrown and can be dealt with.
-More sophisticated applications might browse the server's indexes to
-create a ScanSet, from which indexed terms may be retrieved; others
+
+More sophisticated applications might also browse the server's indexes
+to create a ScanSet, from which indexed terms may be retrieved; others
might send ``Extended Services'' Packages to the server, to achieve
non-standard tasks such as database creation and record update.
Searching using a query syntax other than PQF can be done using an
may be manipulated independently of the objects they are associated
with using an Options object.
+In general, method calls throw an exception if anything goes wrong, so
+you don't need to test for success after each call. See the section
+below on the Exception class for details.
+
+=head1 UTILITY FUNCTION
+
+=head2 ZOOM::diag_str()
+
+ $msg = ZOOM::diag_str(ZOOM::Error::INVALID_QUERY);
+
+Returns a human-readable English-language string corresponding to the
+error code that is its own parameter. This works for any error-code
+returned from
+C<ZOOM::Exception::code()>,
+C<ZOOM::Connection::error_x()>
+or
+C<ZOOM::Connection::errcode()>,
+irrespective of whether it is a member of the C<ZOOM::Error>
+enumeration or drawn from the BIB-1 diagnostic set.
+
+=head1 CLASSES
+
+The eight ZOOM classes are described here in ``sensible order'':
+first, the four commonly used classes, in the he order that they will
+tend to be used in most programs (Connection, ResultSet, Record,
+Exception); then the four more esoteric classes in descending order of
+how often they are needed.
+
+With the exception of the Options class, which is an extension to the
+ZOOM model, the introduction to each class includes a link to the
+relevant section of the ZOOM Abstract API.
+
+=head2 ZOOM::Connection
+
+ $conn = new ZOOM::Connection("indexdata.dk:210/gils");
+ print("server is '", $conn->option("serverImplementationName"), "'\n");
+ $conn->option(preferredRecordSyntax => "usmarc");
+ $rs = $conn->search_pqf('@attr 1=4 mineral');
+ $ss = $conn->scan('@attr 1=1003 a');
+ if ($conn->errcode() != 0) {
+ die("somthing went wrong: " . $conn->errmsg())
+ }
+ $conn->destroy()
+
+This class represents a connection to an information retrieval server,
+using an IR protocol such as ANSI/NISO Z39.50, SRW (the
+Search/Retrieve Webservice), SRU (the Search/Retrieve URL) or
+OpenSearch. Not all of these protocols require a low-level connection
+to be maintained, but the Connection object nevertheless provides a
+location for the necessary cache of configuration and state
+information, as well as a uniform API to the connection-oriented
+facilities (searching, index browsing, etc.), provided by these
+protocols.
+
+See the description of the C<Connection> class in the ZOOM Abstract
+API at
+http://zoom.z3950.org/api/zoom-current.html#3.2
+
+=head3 Methods
+
+=head4 new()
+
+ $conn = new ZOOM::Connection("indexdata.dk", 210);
+ $conn = new ZOOM::Connection("indexdata.dk:210/gils");
+ $conn = new ZOOM::Connection("tcp:indexdata.dk:210/gils");
+ $conn = new ZOOM::Connection("http:indexdata.dk:210/gils");
+
+Creates a new Connection object, and immediately connects it to the
+specified server. If you want to make a new Connection object but
+delay forging the connection, use the C<create()> and C<connect()>
+methods instead.
+
+This constructor can be called with two arguments or a single
+argument. In the former case, the arguments are the name and port
+number of the Z39.50 server to connect to; in the latter case, the
+single argument is a YAZ service-specifier string of the form
+
+=over 4
+
+=item
+
+[I<scheme>:]I<host>[:I<port>][/I<databaseName>]
+
+=back
+
+In which the I<host> and I<port> parts are as in the two-argument
+form, the I<databaseName> if provided specifies the name of the
+database to be used in subsequent searches on this connection, and the
+optional I<scheme> (default C<tcp>) indicates what protocol should be
+used. At present, the following schemes are supported:
+
+=over 4
+
+=item tcp
+
+Z39.50 connection.
+
+=item ssl
+
+Z39.50 connection encrypted using SSL (Secure Sockets Layer). Not
+many servers support this, but Index Data's Zebra is one that does.
+
+=item unix
+
+Z39.50 connection on a Unix-domain (local) socket, in which case the
+I<hostname> portion of the string is instead used as a filename in the
+local filesystem.
+
+=item http
+
+SRW connection using SOAP over HTTP.
+
+=back
+
+Support for SRU will follow in the fullness of time.
+
+If an error occurs, an exception is thrown. This may indicate a
+networking problem (e.g. the host is not found or unreachable), or a
+protocol-level problem (e.g. a Z39.50 server rejected the Init
+request).
+
+=head4 create() / connect()
+
+ $options = new ZOOM::Options();
+ $options->option(implementationName => "my client");
+ $conn = create ZOOM::Connection($options)
+ $conn->connect($host, 0);
+
+The usual Connection constructor, C<new()> brings a new object into
+existence and forges the connection to the server all in one
+operation, which is often what you want. For applications that need
+more control, however, these two method separate the two steps,
+allowing additional steps in between such as the setting of options.
+
+C<create()> creates and returns a new Connection object, which is
+I<not> connected to any server. It may be passed an options block, of
+type C<ZOOM::Options> (see below), into which options may be set
+before or after the creation of the Connection. The connection to the
+server may then be forged by the C<connect()> method, the arguments of
+which are the same as those of the C<new()> constructor.
+
+=head4 error_x() / errcode() / errmsg() / addinfo() / diagset()
+
+ ($errcode, $errmsg, $addinfo, $diagset) = $conn->error_x();
+ $errcode = $conn->errcode();
+ $errmsg = $conn->errmsg();
+ $addinfo = $conn->addinfo();
+ $diagset = $conn->diagset();
+
+These methods may be used to obtain information about the last error
+to have occurred on a connection - although typically they will not
+been used, as the same information is available through the
+C<ZOOM::Exception> that is thrown when the error occurs. The
+C<errcode()>,
+C<errmsg()>,
+C<addinfo()>
+and
+C<diagset()>
+methods each return one element of the diagnostic, and
+C<error_x()>
+returns all four at once.
+
+See the C<ZOOM::Exception> for the interpretation of these elements.
+
+=head4 option() / option_binary()
+
+ print("server is '", $conn->option("serverImplementationName"), "'\n");
+ $conn->option(preferredRecordSyntax => "usmarc");
+ $conn->option_binary(iconBlob => "foo\0bar");
+ die if length($conn->option_binary("iconBlob") != 7);
+
+Objects of the Connection, ResultSet, ScanSet and Package classes
+carry with them a set of named options which affect their behaviour in
+certain ways. See the ZOOM-C options documentation for details:
+
+=over 4
+
+=item *
+
+Connection options are listed at
+http://indexdata.com/yaz/doc/zoom.tkl#zoom.connections
+
+=item *
+
+ScanSet options are listed at
+http://indexdata.com/yaz/doc/zoom.scan.tkl
+I<### move this obvservation down to the appropriate place>
+
+=item *
+
+Package options are listed at
+http://indexdata.com/yaz/doc/zoom.ext.html
+I<### move this obvservation down to the appropriate place>
+
+=back
+
+These options are set and fetched using the C<option()> method, which
+may be called with either one or two arguments. In the two-argument
+form, the option named by the first argument is set to the value of
+the second argument, and its old value is returned. In the
+one-argument form, the value of the specified option is returned.
+
+For historical reasons, option values are not binary-clean, so that a
+value containing a NUL byte will be returned in truncated form. The
+C<option_binary()> method behaves identically to C<option()> except
+that it is binary-clean, so that values containing NUL bytes are set
+and returned correctly.
+
+=head4 search() / search_pqf()
+
+ $rs = $conn->search(new ZOOM::Query::CQL('title=dinosaur'));
+ # The next two lines are equivalent
+ $rs = $conn->search(new ZOOM::Query::PQF('@attr 1=4 dinosaur'));
+ $rs = $conn->search_pqf('@attr 1=4 dinosaur');
+
+The principal purpose of a search-and-retrieve protocol is searching
+(and, er, retrieval), so the principal method used on a Connection
+object is C<search()>. It accepts a single argument, a C<ZOOM::Query>
+object (or, more precisely, an object of a subclass of this class);
+and it creates and returns a new ResultSet object representing the set
+of records resulting from the search.
+
+Since queries using PQF (Prefix Query Format) are so common, we make
+them a special case by providing a C<search_prefix()> method. This is
+identical to C<search()> except that it accepts a string containing
+the query rather than an object, thereby obviating the need to create
+a C<ZOOM::Query::PQF> object. See the documentation of that class for
+information about PQF.
+
+=head4 scan()
+
+Many Z39.50 servers allow you to browse their indexes to find terms to
+search for. This is done using the C<scan> method, which creates and
+returns a new ScanSet object representing the set of terms resulting
+from the scan.
+
+C<scan()> takes a single argument, but it has to work hard: it
+specifies both what index to scan for terms, and where in the index to
+start scanning. What's more, the specification of what index to scan
+includes multiple facets, such as what database fields it's an index
+of (author, subject, title, etc.) and whether to scan for whole fields
+or single words (e.g. the title ``I<The Empire Strikes Back>'', or the
+four words ``Back'', ``Empire'', ``Strikes'' and ``The'', interleaved
+with words from other titles in the same index.
+
+All of this is done by using a single term from the PQF query as the
+C<scan()> argument. (At present, only PQF is supported, although
+there is no reason in principle why CQL and other query syntaxes
+should not be supported in future). The attributes associated with
+the term indicate which index is to be used, and the term itself
+indicates the point in the index at which to start the scan. For
+example, if the argument is C<@attr 1=4 fish>, then
+
+=over 4
+
+=item @attr 1=4
+
+This is the BIB-1 attribute with type 1 (meaning access-point, which
+specifies an index), and type 4 (which means ``title''). So the scan
+is in the title index.
+
+=item fish
+
+Start the scan from the lexicographically earliest term that is equal
+to or falls after ``fish''.
+
+=back
+
+The argument C<@attr 1=4 @attr 6=3 fish> would behave similarly; but
+the BIB-1 attribute 6=3 mean completeness=``complete field'', so the
+scan would be for complete titles rather than for words occurring in
+titles.
+
+This takes a bit of getting used to.
+
+The behaviour is C<scan()> is affected by the following options, which
+may be set on the Connection through which the scan is done:
+
+=over 4
+
+=item number [default: 10]
+
+Indicates how many terms should be returned in the ScanSet. The
+number actually returned may be less, if the start-point is near the
+end of the index, but will not be greater.
+
+=item position [default: 1]
+
+A 1-based index specifying where in the returned list of terms the
+seed-term should appear. By default it should be the first term
+returned, but C<position> may be set, for example, to zero (requesting
+the next terms I<after> the seed-term), or to the same value as
+C<number> (requesting the index terms I<before> the seed term).
+
+=item stepSize [default: 0]
+
+An integer indicating how many indexed terms are to be skipped between
+each one returned in the ScanSet. By default, no terms are skipped,
+but overriding this can be useful to get a high-level overview of the
+index.
+
+=back
+
+=head4 package()
+
+ $p = $conn->package();
+ $o = new ZOOM::Options();
+ $o->option(databaseName => "newdb");
+ $p = $conn->package($o);
+
+Creates and returns a new C<ZOOM::Package>, to be used in invoking an
+Extended Service. An options block may optionally be passed in. See
+the C<ZOOM::Package> documentation.
+
+=head4 destroy()
+
+ $conn->destroy()
+
+Destroys a Connection object, tearing down any low-level connection
+associated with it and freeing its resources. It is an error to reuse
+a Connection that has been C<destroy()>ed.
+
+=head2 ZOOM::ResultSet
+
+ $rs = $conn->search_pqf('@attr 1=4 mineral');
+ $n = $rs->size();
+ for $i (1 .. $n) {
+ $rec = $rs->record($i-1);
+ print $rec->render();
+ }
+
+A ResultSet object represents the set of zero or more records
+resulting from a search, and is the means whereby these records can be
+retrieved. A ResultSet object may maintain client side cache or some,
+less, none, all or more of the server's records: in general, this is
+supposed to an implementaton detail of no interest to a typical
+application, although more sophisticated applications do have
+facilities for messing with the cache. Most applications will only
+need the C<size()>, C<record()> and C<sort()> methods.
+
+There is no C<new()> method nor any other explicit constructor. The
+only way to create a new ResultSet is by using C<search()> (or
+C<search_prefix()>) on a Connection.
+
+See the description of the C<Result Set> class in the ZOOM Abstract
+API at
+http://zoom.z3950.org/api/zoom-current.html#3.4
+
+=head3 Methods
+
+=head4 option()
+
+ $conn->option(elementSetName => "f");
+
+Allows options to be set into, and read from a ResultSet, just like
+the Connection class's C<option()> method. There is no
+C<option_binary()> method for ResultSet objects.
+
+ResultSet options are listed at
+http://indexdata.com/yaz/doc/zoom.resultsets.tkl
+
+=head4 size()
+
+ print "Found ", $rs->size(), " records\n";
+
+Returns the number of records in the result set.
+
+=head4 record(), record_immediate()
+
+ $rec = $rs->record(0);
+ $rec2 = $rs->record_immediate(0);
+ $rec3 = $rs->record_immediate(1)
+ or print "second record wasn't in cache\n";
+
+The C<record()> method returns a C<ZOOM::Record> object representing
+a record from result-set, whose position is indicated by the argument
+passed in. This is a zero-based index, so that legitimate values
+range from zero to C<$rs->size()-1>.
+
+The C<record_immediate()> API is identical, but it never invokes a
+network operation, merely returning the record from the ResultSet's
+cache if it's already there, or an undefined value otherwise. So if
+you use this method, B<you must always check the return value>.
+
+=head4 records()
+
+ $rs->records(0, 10, 0);
+ for $i (0..10) {
+ print $rs->record_immediate($i)->render();
+ }
+
+ @nextseven = $rs->records(10, 7, 1);
+
+The C<record_immediate()> method only fetches records from the cache,
+whereas C<record()> fetches them from the server if they have not
+already been cached; but the ZOOM module has to guess what the most
+efficient strategy for this is. It might fetch each record, alone
+when asked for: that's optimal in an application that's only
+interested in the top hit from each search, but pessimal for one that
+wants to display a whole list of results. Conversely, the software's
+strategy might be always to ask for blocks of a twenty records:
+that's great for assembling long lists of things, but wasteful when
+only one record is wanted. The problem is that the ZOOM module can't
+tell, when you call C<$rs->record()>, what your intention is.
+
+But you can tell it. The C<records()> method fetches a sequence of
+records, all in one go. It takes three arguments: the first is the
+zero-based index of the first record in the sequence, the second is
+the number of records to fetch, and the third is a boolean indication
+of whether or not to return the retrieved records as well as adding
+them to the cache. (You can always pass 1 for this if you like, and
+Perl will discard the unused return value, but there is a small
+efficiency gain to be had by passing 0.)
+
+Once the records have been retrieved from the server
+(i.e. C<records()> has completed without throwing an exception), they
+can be fetched much more efficiently using C<record()> - or
+C<record_immediate(), which is then guaranteed to succeed.
+
+=head4 cache_reset()
+
+ $rs->cache_reset()
+
+Resets the ResultSet's record cache, so that subsequent invocations of
+C<record_immediate()> will fail. I struggle to imagine a real
+scenario where you'd want to do this.
+
+=head4 sort()
+
+ if ($rs->sort("yaz", "1=4 >i") < 0) {
+ die "sort failed";
+ }
+
+Sorts the ResultSet in place ###
+
+=head4 destroy()
+
+ $rs->destroy()
+
+Destroys a ResultSet object, freeing its resources. It is an error to
+reuse a ResultSet that has been C<destroy()>ed.
+
+=head2 ZOOM::Record
+
+I<###>
+
+=head2 ZOOM::Exception
+
+In general, method calls throw an exception (of class
+C<ZOOM::Exception>) if anything goes wrong, so you don't need to test
+for success after each call. Exceptions are caught by enclosing the
+main code in an C<eval{}> block and checking C<$@> on exit from that
+block, as in the code-sample above.
+
+There are a small number of exceptions to this rule: the three
+record-fetching methods in the C<ZOOM::ResultSet> class,
+C<record()>,
+C<record_immediate()>,
+and
+C<records()>
+can all return undefined values for legitimate reasons, under
+circumstances that do not merit throwing an exception. For this
+reason, the return values of these methods should be checked. See the
+individual methods' documentation for details.
+
+=head3 Methods
+
+I<###>
+
+=head2 ZOOM::ScanSet
+
+I<###>
+
+=head2 ZOOM::Package
+
+I<###>
+
+=head2 ZOOM::Query
+
+I<###>
+
+=head2 ZOOM::Options
+
+I<###>
+
+=head1 ENUMERATIONS
+
+The ZOOM module provides two enumerations that list possible return
+values from particular functions. They are described in the following
+sections.
+
+=head2 ZOOM::Error
+
+ if ($@->code() == ZOOM::Error::QUERY_PQF) {
+ return "your query was not accepted";
+ }
+
+This class provides a set of manifest constants representing some of
+the possible error codes that can be raised by the ZOOM module. The
+methods that return error-codes are
+C<ZOOM::Exception::code()>,
+C<ZOOM::Connection::error_x()>
+and
+C<ZOOM::Connection::errcode()>.
+
+The C<ZOOM::Error> class provides the constants
+C<NONE>,
+C<CONNECT>,
+C<MEMORY>,
+C<ENCODE>,
+C<DECODE>,
+C<CONNECTION_LOST>,
+C<INIT>,
+C<INTERNAL>,
+C<TIMEOUT>,
+C<UNSUPPORTED_PROTOCOL>,
+C<UNSUPPORTED_QUERY>,
+C<INVALID_QUERY>,
+C<CREATE_QUERY>,
+C<QUERY_CQL>,
+C<QUERY_PQF>,
+C<SORTBY>,
+C<CLONE>,
+C<PACKAGE>
+and
+C<SCANTERM>,
+each of which specifies a client-side error. Since errors may also be
+diagnosed by the server, and returned to the client, error codes may
+also take values from the BIB-1 diagnostic set of Z39.50, listed at
+the Z39.50 Maintenance Agency's web-site at
+http://www.loc.gov/z3950/agency/defns/bib1diag.html
+
+All error-codes, whether client-side from the C<ZOOM::Error>
+enumeration or server-side from the BIB-1 diagnostic set, can be
+translated into human-readable messages by passing them to the
+C<ZOOM::diag_str()> utility function.
+
+=head2 ZOOM::Event
+
+ if ($conn->last_event() == ZOOM::Event::CONNECT) {
+ print "Connected!\n";
+ }
+
+In applications that need it - mostly complex multiplexing
+applications - The C<ZOOM::Connection::last_event()> method is used to
+return an indication of the last event that occurred on a particular
+connection. It always returns a value drawn from this enumeration,
+that is, one of C<NONE>, C<CONNECT>, C<SEND_DATA>, C<RECV_DATA>,
+C<TIMEOUT>, C<UNKNOWN>, C<SEND_APDU>, C<RECV_APDU>, C<RECV_RECORD> or
+C<RECV_SEARCH>.
+
+You almost certainly don't need to know about this. Frankly, I'm not
+sure how to use it myself.
=head1 SEE ALSO
+The ZOOM abstract API,
+http://zoom.z3950.org/api/zoom-current.html
+
The C<Net::Z3950::ZOOM> module, included in the same distribution as this one.
The C<Net::Z3950> module, which this one supersedes.
+http://perl.z3950.org/
+
+The documentation for the ZOOM-C module of the YAZ Toolkit, which this
+module is built on. Specifically, its lists of options are useful.
+http://indexdata.com/yaz/doc/zoom.tkl
+
+The BIB-1 diagnostic set of Z39.50,
+http://www.loc.gov/z3950/agency/defns/bib1diag.html
=head1 AUTHOR