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ZOOM - Perl extension implementing the ZOOM API for Information Retrieval


 use ZOOM;
 eval {
     $conn = new ZOOM::Connection($host, $port,
                                  databaseName => "mydb");
     $conn->option(preferredRecordSyntax => "usmarc");
     $rs = $conn->search_pqf('@attr 1=4 dinosaur');
     $n = $rs->size();
     print $rs->record(0)->render();
 if ($@) {
     print "Error ", $@->code(), ": ", $@->message(), "\n";


This module provides a nice, Perlish implementation of the ZOOM Abstract API described and documented at

The ZOOM module is implemented as a set of thin classes on top of the non-OO functions provided by this distribution's Net::Z3950::ZOOM module, which in turn is a thin layer on top of the ZOOM-C code supplied as part of Index Data's YAZ Toolkit. Because ZOOM-C is also the underlying code that implements ZOOM bindings in C++, Visual Basic, Scheme, Ruby, .NET (including C#) and other languages, this Perl module works compatibly with those other implementations. (Of course, the point of a public API such as ZOOM is that all implementations should be compatible anyway; but knowing that the same code is running is reassuring.)

The ZOOM module provides two enumerations (ZOOM::Error and ZOOM::Event), three utility functions diag_str(), event_str() and event() in the ZOOM package itself, and eight classes: ZOOM::Exception, ZOOM::Options, ZOOM::Connection, ZOOM::Query, ZOOM::ResultSet, ZOOM::Record, ZOOM::ScanSet and ZOOM::Package. Of these, the Query class is abstract, and has four concrete subclasses: ZOOM::Query::CQL, ZOOM::Query::PQF, ZOOM::Query::CQL2RPN and ZOOM::Query::CCL2RPN. Finally, it also provides a ZOOM::Query::Log module which supplies a useful general-purpose logging facility. Many useful ZOOM applications can be built using only the Connection, ResultSet, Record and Exception classes, as in the example code-snippet above.

A typical application will begin by creating a 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 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 a query object of one of the Query subclasses. Finally, sets of options may be manipulated independently of the objects they are associated with, by 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.



 $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 ZOOM::Exception::code(), ZOOM::Connection::error_x() or ZOOM::Connection::errcode(), irrespective of whether it is a member of the ZOOM::Error enumeration or drawn from the BIB-1 diagnostic set.


 $msg = ZOOM::diag_srw_str(18);

Returns a human-readable English-language string corresponding to the specified SRW error code.


 $msg = ZOOM::event_str(ZOOM::Event::RECV_APDU);

Returns a human-readable English-language string corresponding to the event code that is its own parameter. This works for any value of the ZOOM::Event enumeration.


 $connsRef = [ $conn1, $conn2, $conn3 ];
 $which = ZOOM::event($connsRef);
 $ev = $connsRef->[$which-1]->last_event()
     if ($which != 0);

Used only in complex asynchronous applications, this function takes a reference to a list of Connection objects, waits until an event occurs on any one of them, and returns an integer indicating which of the connections it occurred on. The return value is a 1-based index into the list; 0 is returned if no event occurs within the longest timeout specified by the timeout options of all the connections.

See the section below on asynchronous applications.


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.


 $conn = new ZOOM::Connection("");
 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())

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 Connection class in the ZOOM Abstract API at



 $conn = new ZOOM::Connection("", 210);
 $conn = new ZOOM::Connection("");
 $conn = new ZOOM::Connection("");
 $conn = new ZOOM::Connection("");
 $conn = new ZOOM::Connection("", 210,
                               databaseName => "mydb",
                               preferredRecordSyntax => "marc");

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 create() and 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

When the two-option form is used (which may be done using a vacuous second argument of zero), any number of additional argument pairs may be provided, which are interpreted as key-value pairs to be set as options after the Connection object is created, but before it is connected to the server. This is a convenient way to set options, including those that must be set before connecting such as authentication tokens.

The server-name string is of the form:

  • [scheme:]host[:port][/databaseName]

In which the host and port parts are as in the two-argument form, the databaseName if provided specifies the name of the database to be used in subsequent searches on this connection, and the optional scheme (default tcp) indicates what protocol should be used. At present, the following schemes are supported:


Z39.50 connection.


Z39.50 connection encrypted using SSL (Secure Sockets Layer). Not many servers support this, but Index Data's Zebra is one that does.


Z39.50 connection on a Unix-domain (local) socket, in which case the hostname portion of the string is instead used as a filename in the local filesystem.


SRU connection over HTTP.

If the http scheme is used, the particular SRU flavour to be used may be specified by the sru option, which takes the following values:


SRU over SOAP (i.e. what used to be called SRW). This is the default.


"SRU Classic" (i.e. SRU over HTTP GET).



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).

create() / connect()

 $options = new ZOOM::Options();
 $options->option(implementationName => "my client");
 $options->option(implementationId => 12345);
 $conn = create ZOOM::Connection($options)
 # or
 $conn = create ZOOM::Connection(implementationName => "my client",
                                 implementationId => 12345);

 $conn->connect($host, 0);

The usual Connection constructor, 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 methods separate the two steps, allowing additional steps in between such as the setting of options.

create() creates and returns a new Connection object, which is not connected to any server. It may be passed an options block, of type ZOOM::Options (see below), into which options may be set before or after the creation of the Connection. Alternatively and equivalently, create() may be passed a list of key-value option pairs directly. The connection to the server may then be forged by the connect() method, which accepts hostname and port arguments like those of the new() constructor.

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 ZOOM::Exception that is thrown when the error occurs. The errcode(), errmsg(), addinfo() and diagset() methods each return one element of the diagnostic, and error_x() returns all four at once.

See the ZOOM::Exception for the interpretation of these elements.


 die $conn->exception();

exception() returns the same information as error_x() in the form of a ZOOM::Exception object which may be thrown or rendered. If no error occurred on the connection, then exception() returns an undefined value.



Checks whether an error is pending on the connection, and throw a ZOOM::Exception object if so. Since errors are thrown as they occur for synchronous connections, there is no need ever to call this except in asynchronous applications.

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:

Connection options are listed at

These options are set and fetched using the 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 option_binary() method behaves identically to option() except that it is binary-clean, so that values containing NUL bytes are set and returned correctly.

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 search(). It accepts a single argument, a 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 search_pqf() method. This is identical to search() except that it accepts a string containing the query rather than an object, thereby obviating the need to create a ZOOM::Query::PQF object. See the documentation of that class for information about PQF.

scan() / scan_pqf()

 $rs = $conn->scan(new ZOOM::Query::CQL('title=dinosaur'));
 # The next two lines are equivalent
 $rs = $conn->scan(new ZOOM::Query::PQF('@attr 1=4 dinosaur'));
 $rs = $conn->scan_pqf('@attr 1=4 dinosaur');

Many Z39.50 servers allow you to browse their indexes to find terms to search for. This is done using the scan method, which creates and returns a new ScanSet object representing the set of terms resulting from the scan.

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 ``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 Query object representing a query of a single term as the scan() argument. 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 the query @attr 1=4 fish, then

@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.


Start the scan from the lexicographically earliest term that is equal to or falls after ``fish''.

The argument @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 of scan() is affected by the following options, which may be set on the Connection through which the scan is done:

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.

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 position may be set, for example, to zero (requesting the next terms after the seed-term), or to the same value as number (requesting the index terms before the seed term).

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.

Since scans using PQF (Prefix Query Format) are so common, we make them a special case by providing a scan_pqf() method. This is identical to scan() except that it accepts a string containing the query rather than an object, thereby obviating the need to create a ZOOM::Query::PQF object.


 $p = $conn->package();
 $o = new ZOOM::Options();
 $o->option(databaseName => "newdb");
 $p = $conn->package($o);

Creates and returns a new ZOOM::Package, to be used in invoking an Extended Service. An options block may optionally be passed in. See the ZOOM::Package documentation.


 if ($conn->last_event() == ZOOM::Event::CONNECT) {
     print "Connected!\n";

Returns a ZOOM::Event enumerated value indicating the type of the last event that occurred on the connection. This is used only in complex asynchronous applications - see the sections below on the ZOOM::Event enumeration and asynchronous applications.



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 destroy()ed.


 $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 of some, less, none, all or more of the server's records: in general, this is supposed to be an implementation 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 size(), record() and sort() methods.

There is no new() method, nor any other explicit constructor. The only way to create a new ResultSet is by using search() (or search_pqf()) on a Connection.

See the description of the Result Set class in the ZOOM Abstract API at



 $rs->option(elementSetName => "f");

Allows options to be set into, and read from, a ResultSet, just like the Connection class's option() method. There is no option_binary() method for ResultSet objects.

ResultSet options are listed at


 print "Found ", $rs->size(), " records\n";

Returns the number of records in the result set.

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 record() method returns a 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 $rs->size()-1.

The 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, you must always check the return value.


 $rs->records(0, 10, 0);
 for $i (0..10) {
     print $rs->record_immediate($i)->render();

 @nextseven = $rs->records(10, 7, 1);

The record_immediate() method only fetches records from the cache, whereas 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 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 $rs->record(), what your intention is.

But you can tell it. The 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. records() has completed without throwing an exception), they can be fetched much more efficiently using record() - or record_immediate(), which is then guaranteed to succeed.



Resets the ResultSet's record cache, so that subsequent invocations of record_immediate() will fail. I struggle to imagine a real scenario where you'd want to do this.


 if ($rs->sort("yaz", "1=4 >i 1=21 >s") < 0) {
     die "sort failed";

Sorts the ResultSet in place (discarding any cached records, as they will in general be sorted into a different position). There are two arguments: the first is a string indicating the type of the sort-specification, and the second is the specification itself.

The sort() method returns 0 on success, or -1 if the sort-specification is invalid.

At present, the only supported sort-specification type is yaz. Such a specification consists of a space-separated sequence of keys, each of which itself consists of two space-separated words (so that the total number of words in the sort-specification is even). The two words making up each key are a field and a set of flags. The field can take one of two forms: if it contains an = sign, then it is a BIB-1 type=value pair specifying which field to sort (e.g. 1=4 for a title sort); otherwise it is sent for the server to interpret as best it can. The word of flags is made up from one or more of the following: s for case sensitive, i for case insensitive; < for ascending order and > for descending order.

For example, the sort-specification in the code-fragment above will sort the records in $rs case-insensitively in descending order of title, with records having equivalent titles sorted case-sensitively in ascending order of subject. (The BIB-1 access points 4 and 21 represent title and subject respectively.)



Destroys a ResultSet object, freeing its resources. It is an error to reuse a ResultSet that has been destroy()ed.


 $rec = $rs->record($i);
 print $rec->render();
 $raw = $rec->raw();
 $marc = new_from_usmarc MARC::Record($raw);
 print "Record title is: ", $marc->title(), "\n";

A Record object represents a record that has been retrieved from the server.

There is no new() method, nor any other explicit constructor. The only way to create a new Record is by using record() (or record_immediate(), or records()) on a ResultSet.

In general, records are ``owned'' by their result-sets that they were retrieved from, so they do not have to be explicitly memory-managed: they are deallocated (and therefore can no longer be used) when the result-set is destroyed.

See the description of the Record class in the ZOOM Abstract API at


error() / exception()

 if ($rec->error()) {
     my($code, $msg, $addinfo, $dset) = $rec->error();
     print "error $code, $msg ($addinfo) from $dset set\n";
     die $rec->exception();

These functions test for surrogate diagnostics associated with a record: that is, errors pertaining to a particular record rather than to the fetch-some-records operation as a whole. (The latter are known in Z39.50 as non-surrogate diagnostics, and are reported as exceptions thrown by searches.) If a particular record can't be obtained - for example, because it is not available in the requested record syntax - then the record object obtained from the result-set, when interrogated with these functions, will report the error.

error() returns the error-code, a human-readable message, additional information and the name of the diagnostic set that the error is from. When called in a scalar context, it just returns the error-code. Since error 0 means "no error", it can be used as a boolean has-there-been-an-error indicator.

exception() returns the same information in the form of a ZOOM::Exception object which may be thrown or rendered. If no error occurred on the record, then exception() returns an undefined value.


 print $rec->render();
 print $rec->render("charset=latin1,utf8");

Returns a human-readable representation of the record. Beyond that, no promises are made: careful programs should not make assumptions about the format of the returned string.

If the optional argument is provided, then it is interpreted as in the get() method (q.v.)

This method is useful mostly for debugging.


 use MARC::Record;
 $raw = $rec->raw();
 $marc = new_from_usmarc MARC::Record($raw);
 $trans = $rec->render("charset=latin1,utf8");

Returns an opaque blob of data that is the raw form of the record. Exactly what this is, and what you can do with it, varies depending on the record-syntax. For example, XML records will be returned as, well, XML; MARC records will be returned as ISO 2709-encoded blocks that can be decoded by software such as the fine Marc::Record module; GRS-1 record will be ... gosh, what an interesting question. But no-one uses GRS-1 any more, do they?

If the optional argument is provided, then it is interpreted as in the get() method (q.v.)


 $raw = $rec->get("raw");
 $rendered = $rec->get("render");
 $trans = $rec->get("render;charset=latin1,utf8");
 $trans = $rec->get("render", "charset=latin1,utf8");

This is the underlying method used by render() and raw(), and which in turn delegates to the ZOOM_record_get() function of the underlying ZOOM-C library. Most applications will find it more natural to work with render() and raw().

get() may be called with either one or two arguments. The two-argument form is syntactic sugar: the two arguments are simply joined with a semi-colon to make a single argument, so the third and fourth example invocations above are equivalent. The second argument (or portion of the first argument following the semicolon) is used in the type argument of ZOOM_record_get(), as described in This is useful primarily for invoking the character-set transformation - in the examples above, from ISO Latin-1 to UTF-8 Unicode.

clone() / destroy()

 $rec = $rs->record($i);
 $newrec = $rec->clone();
 print $newrec->render();

Usually, it's convenient that Record objects are owned by their ResultSets and go away when the ResultSet is destroyed; but occasionally you need a Record to outlive its parent and destroy it later, explicitly. To do this, clone() the record, keep the new Record object that is returned, and destroy() it when it's no longer needed. This is the only situation in which a Record needs to be destroyed.


In general, method calls throw an exception (of class 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 eval{} block and checking $@ 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 ZOOM::ResultSet class, record(), record_immediate(), and 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.

An exception carries the following pieces of information:


A numeric code that specifies the type of error. This can be checked for equality with known values, so that intelligent applications can take appropriate action.


A human-readable message corresponding with the code. This can be shown to users, but its value should not be tested, as it could vary in different versions or under different locales.

additional information [optional]

A string containing information specific to the error-code. For example, when the error-code is the BIB-1 diagnostic 109 ("Database unavailable"), the additional information is the name of the database that the application tried to use. For some error-codes, there is no additional information at all; for some others, the additional information is undefined, and may just be a human-readable string.

diagnostic set [optional]

A short string specifying the diagnostic set from which the error-code was drawn: for example, ZOOM for a ZOOM-specific error such as ZOOM::Error::MEMORY ("out of memory"), and BIB-1 for a Z39.50 error-code drawn from the BIB-1 diagnostic set.

In theory, the error-code should be interpreted in the context of the diagnostic set from which it is drawn; in practice, nearly all errors are from either the ZOOM or BIB-1 diagnostic sets, and the codes in those sets have been chosen so as not to overlap, so the diagnostic set can usually be ignored.

See the description of the Exception class in the ZOOM Abstract API at



 die new ZOOM::Exception($errcode, $errmsg, $addinfo, $diagset);

Creates and returns a new Exception object with the specified error-code, error-message, additional information and diagnostic set. Applications will not in general need to use this, but may find it useful to simulate ZOOM exceptions. As is usual with Perl, exceptions are thrown using die().

code() / message() / addinfo() / diagset()

 print "Error ", $@->code(), ": ", $@->message(), "\n";
 print "(addinfo '", $@->addinfo(), "', set '", $@->diagset(), "')\n";

These methods, of no arguments, return the exception's error-code, error-message, additional information and diagnostic set respectively.


 print $@->render();

Returns a human-readable rendition of an exception. The "" operator is overloaded on the Exception class, so that an Exception used in a string context is automatically rendered. Among other consequences, this has the useful result that a ZOOM application that died due to an uncaught exception will emit an informative message before exiting.


 $ss = $conn->scan('@attr 1=1003 a');
 $n = $ss->size();
 ($term, $occ) = $ss->term($n-1);
 $rs = $conn->search_pqf('@attr 1=1003 "' . $term . "'");
 assert($rs->size() == $occ);

A ScanSet represents a set of candidate search-terms returned from an index scan. Its sole purpose is to provide access to those terms, to the corresponding display terms, and to the occurrence-counts of the terms.

There is no new() method, nor any other explicit constructor. The only way to create a new ScanSet is by using scan() on a Connection.

See the description of the Scan Set class in the ZOOM Abstract API at



 print "Found ", $ss->size(), " terms\n";

Returns the number of terms in the scan set. In general, this will be the scan-set size requested by the number option in the Connection on which the scan was performed [default 10], but it may be fewer if the scan is close to the end of the index.

term() / display_term()

 $ss = $conn->scan('@attr 1=1004 whatever');
 ($term, $occurrences) = $ss->term(0);
 ($displayTerm, $occurrences2) = $ss->display_term(0);
 assert($occurrences == $occurrences2);
 if (user_likes_the_look_of($displayTerm)) {
     $rs = $conn->search_pqf('@attr 1=4 "' . $term . '"');
     assert($rs->size() == $occurrences);

These methods return the scanned terms themselves. term() returns the term in a form suitable for submitting as part of a query, whereas display_term() returns it in a form suitable for displaying to a user. Both versions also return the number of occurrences of the term in the index, i.e. the number of hits that will be found if the term is subsequently used in a query.

In most cases, the term and display term will be identical; however, they may be different in cases where punctuation or case is normalised, or where identifiers rather than the original document terms are indexed.


 print "scan status is ", $ss->option("scanStatus");

Allows options to be set into, and read from, a ScanSet, just like the Connection class's option() method. There is no option_binary() method for ScanSet objects.

ScanSet options are also described, though not particularly informatively, at



Destroys a ScanSet object, freeing its resources. It is an error to reuse a ScanSet that has been destroy()ed.


 $p = $conn->package();
 $p->option(action => "specialUpdate");
 $p->option(recordIdOpaque => 145);
 $p->option(record => content_of("/tmp/record.xml"));

This class represents an Extended Services Package: an instruction to the server to do something not covered by the core parts of the Z39.50 standard (or the equivalent in SRW or SRU). Since the core protocols are read-only, such requests are often used to make changes to the database, such as in the record update example above.

Requesting an extended service is a four-step process: first, create a package associated with the connection to the relevant database; second, set options on the package to instruct the server on what to do; third, send the package (which may result in an exception being thrown if the server cannot execute the requested operations; and finally, destroy the package.

Package options are listed at

The particular options that have meaning are determined by the top-level operation string specified as the argument to send(). For example, when the operation is update (the most commonly used extended service), the action option may be set to any of recordInsert (add a new record, failing if that record already exists), recordDelete (delete a record, failing if it is not in the database). recordReplace (replace a record, failing if an old version is not already present) or specialUpdate (add a record, replacing any existing version that may be present).

For update, the record option should be set to the full text of the XML record to added, deleted or replaced. Depending on how the server is configured, it may extract the record's unique ID from the text (i.e. from a known element such as the 001 field of a MARCXML record), or it may require the unique ID to passed in explicitly using the recordIdOpaque option.

Extended services packages are not currently described in the ZOOM Abstract API at They will be added in a forthcoming version, and will function much as those implemented in this module.



 $p->option(recordIdOpaque => "46696f6e61");

Allows options to be set into, and read from, a Package, just like the Connection class's option() method. There is no option_binary() method for Package objects.

Package options are listed at



Sends a package to the server associated with the Connection that created it. Problems are reported by throwing an exception. The single parameter indicates the operation that the server is being requested to perform, and controls the interpretation of the package's options. Valid operations include:


Request a copy of a nominated object, e.g. place an ILL request.


Create a new database, the name of which is specified by the databaseName option.


Drop an existing database, the name of which is specified by the databaseName option.


Commit changes made to the database within a transaction.


Modify the contents of the database by adding, deleting or replacing records (as described above in the overview of the ZOOM::Package class).


I have no idea what this does.

Although the module is capable of making all these requests, not all servers are capable of executing them. Refusal is indicated by throwing an exception. Problems may also be caused by lack of privileges; so send() must be used with caution, and is perhaps best wrapped in a clause that checks for exceptions, like so:

 eval { $p->send("create") };
 if ($@ && $@->isa("ZOOM::Exception")) {
     print "Oops!  ", $@->message(), "\n";
     return $@->code();



Destroys a Package object, freeing its resources. It is an error to reuse a Package that has been destroy()ed.


 $q = new ZOOM::Query::CQL("creator=pike and subject=unix");
 $q->sortby("1=4 >i 1=21 >s");
 $rs = $conn->search($q);

ZOOM::Query is a virtual base class from which various concrete subclasses can be derived. Different subclasses implement different types of query. The sole purpose of a Query object is to be used in a search() on a Connection; because PQF is such a common special case, the shortcut Connection method search_pqf() is provided.

The following Query subclasses are provided, each providing the same set of methods described below:


Implements Prefix Query Format (PQF), also sometimes known as Prefix Query Notation (PQN). This esoteric but rigorous and expressive format is described in the YAZ Manual at


Implements the Common Query Language (CQL) of SRU, the Search/Retrieve URL. CQL is a much friendlier notation than PQF, using a simple infix notation. The queries are passed ``as is'' to the server rather than being compiled into a Z39.50 Type-1 query, so only CQL-compliant servers can support such queries. CQL is described at and in a slightly out-of-date but nevertheless useful tutorial at


Implements CQL by compiling it on the client-side into a Z39.50 Type-1 (RPN) query, and sending that. This provides essentially the same functionality as ZOOM::Query::CQL, but it will work against any standard Z39.50 server rather than only against the small subset that support CQL natively. The drawback is that, because the compilation is done on the client side, a configuration file is required to direct the mapping of CQL constructs such as index names, relations and modifiers into Type-1 query attributes. An example CQL configuration file is included in the ZOOM-Perl distribution, in the file samples/cql/


Implements CCL by compiling it on the client-side into a Z39.50 Type-1 (RPN) query, and sending that. Because the compilation is done on the client side, a configuration file is required to direct the mapping of CCL constructs such as index names and boolean operators into Type-1 query attributes. An example CCL configuration file is included in the ZOOM-Perl distribution, in the file samples/ccl/default.bib

CCL is syntactically very similar to CQL, but much looser. While CQL is an entirely precise language in which each possible query has rigorously defined semantics, and is thus suitable for transfer as part of a protocol, CCL is best deployed as a human-facing UI language.

See the description of the Query class in the ZOOM Abstract API at



 $q = new ZOOM::Query::CQL('title=dinosaur');
 $q = new ZOOM::Query::PQF('@attr 1=4 dinosaur');

Creates a new query object, compiling the query passed as its argument according to the rules of the particular query-type being instantiated. If compilation fails, an exception is thrown. Otherwise, the query may be passed to the Connection method search().

 $conn->option(cqlfile => "samples/cql/");
 $q = new ZOOM::Query::CQL2RPN('title=dinosaur', $conn);

Note that for the ZOOM::Query::CQL2RPN subclass, the Connection must also be passed into the constructor. This is used for two purposes: first, its cqlfile option is used to find the CQL configuration file that directs the translations into RPN; and second, if compilation fails, then diagnostic information is cached in the Connection and may be retrieved using $conn->errcode() and related methods.

 $conn->option(cclfile => "samples/ccl/default.bib");
 # or
 $conn->option(cclqual => "ti u=4 s=pw\nab u=62 s=pw");
 $q = new ZOOM::Query::CCL2RPN('ti=dinosaur', $conn);

For the ZOOM::Query::CCL2RPN subclass, too, the Connection must be passed into the constructor, for the same reasons as when client-side CQL compilation is used. The cclqual option, if defined, gives a CCL qualification specification inline; otherwise, the contents of the file named by the cclfile option are used.


 $q->sortby("1=4 >i 1=21 >s");

Sets a sort specification into the query, so that when a search() is run on the query, the result is automatically sorted. The sort specification language is the same as the yaz sort-specification type of the ResultSet method sort(), described above.



Destroys a Query object, freeing its resources. It is an error to reuse a Query that has been destroy()ed.


 $o1 = new ZOOM::Options();
 $o1->option(user => "alf");
 $o2 = new ZOOM::Options();
 $o2->option(password => "fruit");
 $opts = new ZOOM::Options($o1, $o2);
 $conn = create ZOOM::Connection($opts);
 $conn->connect($host); # Uses the specified username and password

Several classes of ZOOM objects carry their own sets of options, which can be manipulated using their option() method. Sometimes, however, it's useful to deal with the option sets directly, and the ZOOM::Options class exists to enable this approach.

Option sets are not currently described in the ZOOM Abstract API at They are an extension to that specification.



 $o1 = new ZOOM::Options();
 $o1and2 = new ZOOM::Options($o1);
 $o3 = new ZOOM::Options();
 $o1and3and4 = new ZOOM::Options($o1, $o3);

Creates and returns a new option set. One or two (but no more) existing option sets may be passed as arguments, in which case they become ``parents'' of the new set, which thereby ``inherits'' their options, the values of the first parent overriding those of the second when both have a value for the same key. An option set that inherits from a parent that has its own parents also inherits the grandparent's options, and so on.

option() / option_binary()

 $o->option(preferredRecordSyntax => "usmarc");
 $o->option_binary(iconBlob => "foo\0bar");
 die if length($o->option_binary("iconBlob") != 7);

These methods are used to get and set options within a set, and behave the same way as the same-named Connection methods - see above. As with the Connection methods, values passed to and retrieved using option() are interpreted as NUL-terminated, while those passed to and retrieved from option_binary() are binary-clean.


 $o->option(x => "T");
 $o->option(y => "F");
 assert($o->bool("x", 1));
 assert(!$o->bool("y", 1));
 assert($o->bool("z", 1));

The first argument is a key, and the second is a default value. Returns the value associated with the specified key as a boolean, or the default value if the key has not been set. The values T (upper case) and 1 are considered true; all other values (including t (lower case) and non-zero integers other than one) are considered false.

This method is provided in ZOOM-C because in a statically typed language it's convenient to have the result returned as an easy-to-test type. In a dynamically typed language such as Perl, this problem doesn't arise, so bool() is nearly useless; but it is made available in case applications need to duplicate the idiosyncratic interpretation of truth and falsehood and ZOOM-C uses.


 $o->option(x => "012");
 assert($o->int("x", 20) == 12);
 assert($o->int("y", 20) == 20);

Returns the value associated with the specified key as an integer, or the default value if the key has not been set. See the description of bool() for why you almost certainly don't want to use this.


 $o->set_int(x => "29");

Sets the value of the specified option as an integer. Of course, Perl happily converts strings to integers on its own, so you can just use option() for this, but set_int() is guaranteed to use the same string-to-integer conversion as ZOOM-C does, which might occasionally be useful. Though I can't imagine how.


 sub cb {
     ($udata, $key) = @;
     return "$udata-$key-$udata";
 $o->set_callback(\&cb, "xyz");
 assert($o->option("foo") eq "xyz-foo-xyz");

This method allows a callback function to be installed in an option set, so that the values of options can be calculated algorithmically rather than, as usual, looked up in a table. Along with the callback function itself, an additional datum is provided: when an option is subsequently looked up, this datum is passed to the callback function along with the key; and its return value is returned to the caller as the value of the option.

Warning. Although it ought to be possible to specify callback function using the \&name syntax above, or a literal sub { code } code reference, the complexities of the Perl-internal memory management system mean that the function must currently be specified as a string containing the fully-qualified name, e.g. "main::cb".>

Warning. The current implementation of this method leaks memory, not only when the callback is installed, but on every occasion that it is consulted to look up an option value.



Destroys an Options object, freeing its resources. It is an error to reuse an Options object that has been destroy()ed.


The ZOOM module provides two enumerations that list possible return values from particular functions. They are described in the following sections.


 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 ZOOM::Exception::code(), ZOOM::Connection::error_x() and ZOOM::Connection::errcode().


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

All error-codes, whether client-side from the ZOOM::Error enumeration or server-side from the BIB-1 diagnostic set, can be translated into human-readable messages by passing them to the ZOOM::diag_str() utility function.


 if ($conn->last_event() == ZOOM::Event::CONNECT) {
     print "Connected!\n";

In applications that need it - mostly complex multiplexing applications - The 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 NONE, CONNECT, SEND_DATA, RECV_DATA, TIMEOUT, UNKNOWN, SEND_APDU, RECV_APDU, RECV_RECORD, RECV_SEARCH or ZEND.

See the section below on asynchronous applications.


 ZOOM::Log::log("myapp", "starting up with pid ", $$);

Logging facilities are provided by a set of functions in the ZOOM::Log module. Note that ZOOM::Log is not a class, and it is not possible to create ZOOM::Log objects: the API is imperative, reflecting that of the underlying YAZ logging facilities. Although there are nine logging functions altogether, you can ignore nearly all of them: most applications that use logging will begin by calling mask_str() and init_level() once each, as above, and will then repeatedly call log().


 $level = ZOOM::Log::mask_str("zoom,myapp,-warn");

Returns an integer corresponding to the log-level specified by the parameter. This is a string of zero or more comma-separated module-names, each indicating an individual module to be either added to the default log-level or removed from it (for those components prefixed by a minus-sign). The names may be those of either standard YAZ-logging modules such as fatal, debug and warn, or custom modules such as myapp in the example above. The module zoom requests logging from the ZOOM module itself, which may be helpful for debugging.

Note that calling this function does not in any way change the logging state: it merely returns a value. To change the state, this value must be passed to init_level().


 $level = ZOOM::Log::module_level("zoom");
 ZOOM::Log::log($level, "all systems clear: thrusters invogriated");

Returns the integer corresponding to the single log-level specified as the parameter, or zero if that level has not been registered by a prior call to mask_str(). Since log() accepts either a numeric log-level or a string, there is no reason to call this function; but, what the heck, maybe you enjoy that kind of thing. Who are we to judge?



Initialises the log-level to the specified integer, which is a bitmask of values, typically as returned from mask_str(). All subsequent calls to log() made with a log-level that matches one of the bits in this mask will result in a log-message being emitted. All logging can be turned off by calling init_level(0).



Initialises a prefix string to be included in all log-messages.



Initialises the output file to be used for logging: subsequent log-messages are written to the nominated file. If this function is not called, log-messages are written to the standard error stream.


 ZOOM::Log::init($level, $0, "/tmp/myapp.log");

Initialises the log-level, the logging prefix and the logging output file in a single operation.


 ZOOM::Log::time_format("%Y-%m-%d %H:%M:%S");

Sets the format in which log-messages' timestamps are emitted, by means of a format-string like that used in the C function strftime(). The example above emits year, month, day, hours, minutes and seconds in big-endian order, such that timestamps can be sorted lexicographically.


(This doesn't seem to work, so I won't bother describing it.)


 ZOOM::Log::log(8192, "reducing to warp-factor $wf");
 ZOOM::Log::log("myapp", "starting up with pid ", $$);

Provided that the first argument, log-level, is among the modules previously established by init_level(), this function emits a log-message made up of a timestamp, the prefix supplied to init_prefix(), if any, and the concatenation of all arguments after the first. The message is written to the standard output stream, or to the file previously specified by init_file() if this has been called.

The log-level argument may be either a numeric value, as returned from module_level(), or a string containing the module name.


Although asynchronous applications are conceptually complex, the ZOOM support for them is provided through a very simple interface, consisting of one option (async), one function (ZOOM::event()), one Connection method (last_event() and an enumeration (ZOOM::Event).

The approach is as follows:


Create several connections to the various servers, each of them having the option async set, and with whatever additional options are required - e.g. the piggyback retrieval record-count can be set so that records will be returned in search responses.


Send searches to the connections, request records, etc.

Event harvesting

Repeatedly call ZOOM::event() to discover what responses are being received from the servers. Each time this function returns, it indicates which of the connections has fired; this connection can then be interrogated with the last_event() method to discover what event has occurred, and the return value - an element of the ZOOM::Event enumeration - can be tested to determine what to do next. For example, the ZEND event indicates that no further operations are outstanding on the connection, so any fetched records can now be immediately obtained.

Here is a very short program (omitting all error-checking!) which demonstrates this process. It parallel-searches three servers (or more if you add them the list), displaying the first record in the result-set of each server as soon as it becomes available.

 use ZOOM;
 @servers = ('',
 for ($i = 0; $i < @servers; $i++) {
     $z[$i] = new ZOOM::Connection($servers[$i], 0,
                                   async => 1, # asynchronous mode
                                   count => 1, # piggyback retrieval count
                                   preferredRecordSyntax => "usmarc");
     $r[$i] = $z[$i]->search_pqf("mineral");
 while (($i = ZOOM::event(\@z)) != 0) {
     $ev = $z[$i-1]->last_event();
     print("connection ", $i-1, ": ", ZOOM::event_str($ev), "\n");
     if ($ev == ZOOM::Event::ZEND) {
         $size = $r[$i-1]->size();
         print "connection ", $i-1, ": $size hits\n";
         print $r[$i-1]->record(0)->render()
             if $size > 0;


The ZOOM abstract API,

The Net::Z3950::ZOOM module, included in the same distribution as this one.

The Net::Z3950 module, which this one supersedes.

The documentation for the ZOOM-C module of the YAZ Toolkit, which this module is built on. Specifically, its lists of options are useful.

The BIB-1 diagnostic set of Z39.50,


Mike Taylor, <>


Copyright (C) 2005-2017 by Index Data.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of Perl 5 you may have available.