.\" Automatically generated by Pod::Man 4.14 (Pod::Simple 3.40) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. Capital omega is used to do unbreakable dashes and .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, .\" nothing in troff, for use with C<>. .tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is >0, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{\ . if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{\ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" ======================================================================== .\" .IX Title "SimpleServer 3pm" .TH SimpleServer 3pm "2020-11-08" "perl v5.32.0" "User Contributed Perl Documentation" .\" For nroff, turn off justification. Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" Net::Z3950::SimpleServer \- Simple Perl API for building Z39.50 servers. .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& use Net::Z3950::SimpleServer; \& \& sub my_search_handler { \& my $args = shift; \& \& my $set_id = $args\->{SETNAME}; \& my @database_list = @{ $args\->{DATABASES} }; \& my $query = $args\->{QUERY}; \& \& ## Perform the query on the specified set of databases \& ## and return the number of hits: \& \& $args\->{HITS} = $hits; \& } \& \& sub my_fetch_handler { # Get a record for the user \& my $args = shift; \& \& my $set_id = $args\->{SETNAME}; \& \& my $record = fetch_a_record($args\->{OFFSET}); \& \& $args\->{RECORD} = $record; \& if (number_of_hits() == $args\->{OFFSET}) { ## Last record in set? \& $args\->{LAST} = 1; \& } else { \& $args\->{LAST} = 0; \& } \& } \& \& ## Register custom event handlers: \& my $z = new Net::Z3950::SimpleServer(GHANDLE = $someObject, \& INIT => \e&my_init_handler, \& CLOSE => \e&my_close_handler, \& SEARCH => \e&my_search_handler, \& FETCH => \e&my_fetch_handler); \& \& ## Launch server: \& $z\->launch_server("ztest.pl", @ARGV); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" The SimpleServer module is a tool for constructing Z39.50 \*(L"Information Retrieval\*(R" servers in Perl. The module is easy to use, but it does help to have an understanding of the Z39.50 query structure and the construction of structured retrieval records. .PP Z39.50 is a network protocol for searching remote databases and retrieving the results in the form of structured \*(L"records\*(R". It is widely used in libraries around the world, as well as in the \s-1US\s0 Federal Government. In addition, it is generally useful whenever you wish to integrate a number of different database systems around a shared, abstract data model. .PP The model of the module is simple: It implements a \*(L"generic\*(R" Z39.50 server, which invokes callback functions supplied by you to search for content in your database. You can use any tools available in Perl to supply the content, including modules like \s-1DBI\s0 and WWW::Search. .PP The server will take care of managing the network connections for you, and it will spawn a new process (or thread, in some environments) whenever a new connection is received. .PP The programmer can specify subroutines to take care of the following type of events: .PP .Vb 7 \& \- Start service (called once). \& \- Initialize request \& \- Search request \& \- Present request \& \- Fetching of records \& \- Scan request (browsing) \& \- Closing down connection .Ve .PP Note that only the Search and Fetch handler functions are required. The module can supply default responses to the other on its own. .PP After the launching of the server, all control is given away from the Perl script to the server. The server calls the registered subroutines to field incoming requests from Z39.50 clients. .PP A reference to an anonymous hash is passed to each handler. Some of the entries of these hashes are to be considered input and others output parameters. .PP The Perl programmer specifies the event handlers for the server by means of the SimpleServer object constructor .PP .Vb 11 \& my $z = new Net::Z3950::SimpleServer( \& START => \e&my_start_handler, \& INIT => \e&my_init_handler, \& CLOSE => \e&my_close_handler, \& SEARCH => \e&my_search_handler, \& PRESENT => \e&my_present_handler, \& SCAN => \e&my_scan_handler, \& FETCH => \e&my_fetch_handler, \& EXPLAIN => \e&my_explain_handler, \& DELETE => \e&my_delete_handler, \& SORT => \e&my_sort_handler); .Ve .PP In addition, the arguments to the constructor may include \s-1GHANDLE,\s0 a global handle which is made available to each invocation of every callback function. This is typically a reference to either a hash or an object. .PP If you want your SimpleServer to start a thread (threaded mode) to handle each incoming Z39.50 request instead of forking a process (forking mode), you need to register the handlers by symbol rather than by code reference. Thus, in threaded mode, you will need to register your handlers this way: .PP .Vb 5 \& my $z = new Net::Z3950::SimpleServer( \& INIT => "my_package::my_init_handler", \& CLOSE => "my_package::my_close_handler", \& .... \& .... ); .Ve .PP where my_package is the Perl package in which your handler is located. .PP After the custom event handlers are declared, the server is launched by means of the method .PP .Vb 1 \& $z\->launch_server("MyServer.pl", @ARGV); .Ve .PP Notice, the first argument should be the name of your server script (for logging purposes), while the rest of the arguments are documented in the \s-1YAZ\s0 toolkit manual: The section on application invocation: .PP In particular, you need to use the \-T switch to start your SimpleServer in threaded mode. .SS "Start handler" .IX Subsection "Start handler" The start handler is called when service is started. The argument hash passed to the start handler has the form .PP .Vb 3 \& $args = { \& CONFIG => "default\-config" ## GFS config (as given by \-c) \& }; .Ve .PP The purpose of the start handler is to read the configuration file for the Generic Frontend Server . This is specified by option \-c. If \-c is omitted, the configuration file is set to \*(L"default-config\*(R". .PP The start handler is optional. It is supported in Simpleserver 1.16 and later. .SS "Init handler" .IX Subsection "Init handler" The init handler is called whenever a Z39.50 client is attempting to logon to the server. The exchange of parameters between the server and the handler is carried out via an anonymous hash reached by a reference, i.e. .PP .Vb 1 \& $args = shift; .Ve .PP The argument hash passed to the init handler has the form .PP .Vb 2 \& $args = { \& ## Response parameters: \& \& PEER_NAME => "", ## Name or IP address of connecting client \& IMP_ID => "", ## Z39.50 Implementation ID \& IMP_NAME => "", ## Z39.50 Implementation name \& IMP_VER => "", ## Z39.50 Implementation version \& ERR_CODE => 0, ## Error code, cnf. Z39.50 manual \& ERR_STR => "", ## Error string (additional info.) \& USER => "xxx" ## If Z39.50 authentication is used, \& ## this member contains user name \& PASS => "yyy" ## Under same conditions, this member \& ## contains the password in clear text \& GHANDLE => $obj ## Global handle specified at creation \& HANDLE => undef ## Handler of Perl data structure \& }; .Ve .PP The \s-1HANDLE\s0 member can be used to store any scalar value which will then be provided as input to all subsequent calls (i.e. for searching, record retrieval, etc.). A common use of the handle is to store a reference to a hash which may then be used to store session-specific parameters. If you have any session-specific information (such as a list of result sets or a handle to a back-end search engine of some sort), it is always best to store them in a private session structure \- rather than leaving them in global variables in your script. .PP The Implementation \s-1ID,\s0 name and version are only really used by Z39.50 client developers to see what kind of server they're dealing with. Filling these in is optional. .PP The \s-1ERR_CODE\s0 should be left at 0 (the default value) if you wish to accept the connection. Any other value is interpreted as a failure and the client will be shown the door, with the code and the associated additional information, \s-1ERR_STR\s0 returned. .SS "Search handler" .IX Subsection "Search handler" Similarly, the search handler is called with a reference to an anonymous hash. The structure is the following: .PP .Vb 2 \& $args = { \& ## Request parameters: \& \& GHANDLE => $obj # Global handle specified at creation \& HANDLE => ref, # Your session reference. \& SETNAME => "id", # ID of the result set \& REPL_SET => 0, # Replace set if already existing? \& DATABASES => ["xxx"], # Reference to a list of databases to search \& QUERY => "query", # The query expression as a PQF string \& RPN => $obj, # Reference to a Net::Z3950::APDU::Query \& CQL => $x, # A CQL query, if this is provided instead of Type\-1 \& SRW_SORTKEYS => $x, # XXX to be described \& PID => $x, # XXX to be described \& PRESENT_NUMBER => $x, # XXX to be described \& EXTRA_ARGS => $x, # XXX to be described \& INPUTFACETS => $x, # Specification of facets required: see below. \& \& ## Response parameters: \& \& ERR_CODE => 0, # Error code (0=Successful search) \& ERR_STR => "", # Error string \& HITS => 0, # Number of matches \& ESTIMATED_HIT_COUNT => $x, # XXX to be described \& EXTRA_RESPONSE_DATA => $x, # XXX to be described \& OUTPUTFACETS => $x # Facets returned: see below. \& }; .Ve .PP Note that a search which finds 0 hits is considered successful in Z39.50 terms \- you should only set the \s-1ERR_CODE\s0 to a non-zero value if there was a problem processing the request. The Z39.50 standard provides a comprehensive list of standard diagnostic codes, and you should use these whenever possible. .PP \fIQuery structures\fR .IX Subsection "Query structures" .PP In Z39.50, the most comment kind of query is the so-called Type\-1 _query, a tree-structure of terms combined by operators, the terms being qualified by lists of attributes. .PP The \s-1QUERY\s0 parameter presented this tree to the search function in the Prefix Query Format (\s-1PQF\s0) which is used in many applications based on the \s-1YAZ\s0 toolkit. The full grammar is described in the \s-1YAZ\s0 manual. .PP The following are all examples of valid queries in the \s-1PQF.\s0 .PP .Vb 1 \& dylan \& \& "bob dylan" \& \& @or "dylan" "zimmerman" \& \& @set Result\-1 \& \& @or @and bob dylan @set Result\-1 \& \& @and @attr 1=1 "bob dylan" @attr 1=4 "slow train coming" \& \& @attrset @attr 4=1 @attr 1=4 "self portrait" .Ve .PP You will need to write a recursive function or something similar to parse incoming query expressions, and this is usually where a lot of the work in writing a database-backend happens. Fortunately, you don't need to support any more functionality than you want to. For instance, it is perfectly legal to not accept boolean operators, but you should try to return good error codes if you run into something you can't or won't support. .PP A more convenient alternative to the \s-1QUERY\s0 member is the \s-1RPN\s0 member, which is a reference to a Net::Z3950::APDU::Query object representing the \s-1RPN\s0 query tree. The structure of that object is supposed to be self-documenting, but here's a brief summary of what you get: .IP "\(bu" 4 \&\f(CW\*(C`Net::Z3950::APDU::Query\*(C'\fR is a hash with two fields: .Sp .RS 4 .ie n .IP """attributeSet""" 4 .el .IP "\f(CWattributeSet\fR" 4 .IX Item "attributeSet" Optional. If present, it is a reference to a \&\f(CW\*(C`Net::Z3950::APDU::OID\*(C'\fR. This is a string of dot-separated integers representing the \s-1OID\s0 of the query's top-level attribute set. .ie n .IP """query""" 4 .el .IP "\f(CWquery\fR" 4 .IX Item "query" Mandatory: a reference to the \s-1RPN\s0 tree itself. .RE .RS 4 .RE .IP "\(bu" 4 Each node of the tree is an object of one of the following types: .Sp .RS 4 .ie n .IP """Net::Z3950::RPN::And""" 4 .el .IP "\f(CWNet::Z3950::RPN::And\fR" 4 .IX Item "Net::Z3950::RPN::And" .PD 0 .ie n .IP """Net::Z3950::RPN::Or""" 4 .el .IP "\f(CWNet::Z3950::RPN::Or\fR" 4 .IX Item "Net::Z3950::RPN::Or" .ie n .IP """Net::Z3950::RPN::AndNot""" 4 .el .IP "\f(CWNet::Z3950::RPN::AndNot\fR" 4 .IX Item "Net::Z3950::RPN::AndNot" .PD These three classes are all arrays of two elements, each of which is a node. .ie n .IP """Net::Z3950::RPN::Term""" 4 .el .IP "\f(CWNet::Z3950::RPN::Term\fR" 4 .IX Item "Net::Z3950::RPN::Term" A query term. See below for details. .ie n .IP """Net::Z3950::RPN::RSID""" 4 .el .IP "\f(CWNet::Z3950::RPN::RSID\fR" 4 .IX Item "Net::Z3950::RPN::RSID" A reference to a result-set \s-1ID\s0 indicating a previous search. The \s-1ID\s0 of the result-set is in the \f(CW\*(C`id\*(C'\fR element. .RE .RS 4 .RE .IP "\(bu" 4 \&\f(CW\*(C`Net::Z3950::RPN::Term\*(C'\fR is a hash with two fields: .Sp .RS 4 .ie n .IP """term""" 4 .el .IP "\f(CWterm\fR" 4 .IX Item "term" A string containing the search term itself. .ie n .IP """attributes""" 4 .el .IP "\f(CWattributes\fR" 4 .IX Item "attributes" A reference to a \f(CW\*(C`Net::Z3950::RPN::Attributes\*(C'\fR object. .RE .RS 4 .RE .IP "\(bu" 4 \&\f(CW\*(C`Net::Z3950::RPN::Attributes\*(C'\fR is an array of references to \&\f(CW\*(C`Net::Z3950::RPN::Attribute\*(C'\fR objects. (Note the plural/singular distinction.) .IP "\(bu" 4 \&\f(CW\*(C`Net::Z3950::RPN::Attribute\*(C'\fR is a hash with three elements: .Sp .RS 4 .ie n .IP """attributeSet""" 4 .el .IP "\f(CWattributeSet\fR" 4 .IX Item "attributeSet" Optional. If present, it is dot-separated \s-1OID\s0 string, as above. .ie n .IP """attributeType""" 4 .el .IP "\f(CWattributeType\fR" 4 .IX Item "attributeType" An integer indicating the type of the attribute \- for example, under the \s-1BIB\-1\s0 attribute set, type 1 indicates a ``use'' attribute, type 2 a ``relation'' attribute, etc. .ie n .IP """attributeValue""" 4 .el .IP "\f(CWattributeValue\fR" 4 .IX Item "attributeValue" An integer or string indicating the value of the attribute \- for example, under \&\s-1BIB\-1,\s0 if the attribute type is 1, then value 4 indicates a title search and 7 indicates an \s-1ISBN\s0 search; but if the attribute type is 2, then value 4 indicates a ``greater than or equal'' search, and 102 indicates a relevance match. .RE .RS 4 .RE .PP All of these classes except \f(CW\*(C`Attributes\*(C'\fR and \f(CW\*(C`Attribute\*(C'\fR are subclasses of the abstract class \f(CW\*(C`Net::Z3950::RPN::Node\*(C'\fR. That class has a single method, \f(CW\*(C`toPQF()\*(C'\fR, which may be used to turn an \s-1RPN\s0 tree, or part of one, back into a textual prefix query. .PP Note that, apart to \f(CW\*(C`toPQF()\*(C'\fR, none of these classes have any methods at all: the blessing into classes is largely just a documentation thing so that, for example, if you do .PP .Vb 1 \& { use Data::Dumper; print Dumper($args\->{RPN}) } .Ve .PP you get something fairly human-readable. But of course, the type distinction between the three different kinds of boolean node is important. .PP By adding your own methods to these classes (building what I call ``augmented classes''), you can easily build code that walks the tree of the incoming \s-1RPN.\s0 Take a look at \f(CW\*(C`samples/render\-search.pl\*(C'\fR for a sample implementation of such an augmented classes technique. .PP Finally, when SimpleServer is invoked using \s-1SRU/SRW\s0 (and indeed using Z39.50 if the unusual type\-104 query is used), the query that is _passed is expressed in \s-1CQL,\s0 the Contextual Query Language. In this case, the query string is made available in the \s-1CQL\s0 argument. .PP \fIFacets\fR .IX Subsection "Facets" .PP Servers may support the provision of facets \*(-- counted lists of field values which may subsequently be be used as query terms to narrow the search. .PP In \s-1SRU,\s0 facets may be requested by the \f(CW\*(C`facetLimit\*(C'\fR parameter, as documented in the \s-1OASIS\s0 standard that formalises the \s-1SRU\s0 specification . Its value is a string consisting of a comma-separated list of facet specifications. Each facet specification consists of of a count, a colon and a fieldname. For example, \f(CW\*(C`facetLimit=10:title,5:author\*(C'\fR asks for ten title facets and five author facets. .PP Request format .IX Subsection "Request format" .PP The facet request is passed to the search-handler function in the \&\s-1INPUTFACETS\s0 parameter. Its value is rather complex, due to backwards compatibility with Z39.50: .IP "\(bu" 4 The top-level value is a \f(CW\*(C`Net::Z3950::FacetList\*(C'\fR array. .IP "\(bu" 4 This is an array of \f(CW\*(C`Net::Z3950::FacetField\*(C'\fR objects. .IP "\(bu" 4 Each of these is an object with two members, \f(CW\*(C`attributes\*(C'\fR and \&\f(CW\*(C`terms\*(C'\fR. .IP "\(bu" 4 \&\f(CW\*(C`attributes\*(C'\fR has type \f(CW\*(C`Net::Z3950::RPN::Attributes\*(C'\fR and is a list of objects of type \f(CW\*(C`Net::Z3950::RPN::Attribute\*(C'\fR. .IP "\(bu" 4 Each attribute has two elements, \f(CW\*(C`attributeType\*(C'\fR and \&\f(CW\*(C`attributeValue\*(C'\fR. Each value is interpreted according to its type. The meanings of the types are as follows: .RS 4 .IP "1." 4 The name of the field to provide values of the facets. .IP "2." 4 The order in which to sort the values. (But it's not clear how this is to be interpreted: it may be implementation dependent.) .IP "3." 4 The number of facets to include for the specified field. .IP "4." 4 The first facet to include in the response: for example, if this is 11, then the first ten facts should be skipped. .RE .RS 4 .RE .PP So for example, the \s-1SRU\s0 facet specification \&\f(CW\*(C`facetLimit=10:title,5:author\*(C'\fR would be translated as a \&\f(CW\*(C`Net::Z3950::FacetList\*(C'\fR list of two \f(CW\*(C`Net::Z3950::FacetField\*(C'\fRs. The \&\f(CW\*(C`attributes\*(C'\fR of the first would be [1=\*(L"title\*(R", 3=10], and those of the second would be [1=\*(L"author\*(R", 3=5]. .PP It is not clear what the purpose of \f(CW\*(C`terms\*(C'\fR is, but for the record, this is how it is represented: .IP "\(bu" 4 \&\f(CW\*(C`terms\*(C'\fR is a \f(CW\*(C`Net::Z3950::FacetTerms\*(C'\fR array. .IP "\(bu" 4 This is an array of \f(CW\*(C`Net::Z3950::FacetTerm\*(C'\fR objects. .IP "\(bu" 4 Each of these is an object with two members, \f(CW\*(C`term\*(C'\fR and \f(CW\*(C`count\*(C'\fR. The first of these is an integer, the second a string. .PP Response format .IX Subsection "Response format" .PP Having generated facets corresponding to the request, the search handler should return them in the \f(CW\*(C`OUTPUTFACETS\*(C'\fR argument. The structure of this response is similar to that of the request: .IP "\(bu" 4 The top-level value is a \f(CW\*(C`Net::Z3950::FacetList\*(C'\fR array. .IP "\(bu" 4 This is an array of \f(CW\*(C`Net::Z3950::FacetField\*(C'\fR objects. .IP "\(bu" 4 Each of these is an object with two members, \f(CW\*(C`attributes\*(C'\fR and \&\f(CW\*(C`terms\*(C'\fR. .IP "\(bu" 4 \&\f(CW\*(C`attributes\*(C'\fR has type \f(CW\*(C`Net::Z3950::RPN::Attributes\*(C'\fR and is a list of objects of type \f(CW\*(C`Net::Z3950::RPN::Attribute\*(C'\fR. .IP "\(bu" 4 Each attribute has two elements, \f(CW\*(C`attributeType\*(C'\fR and \&\f(CW\*(C`attributeValue\*(C'\fR. Each value is interpreted according to its type. The meanings of the types are as follows: .RS 4 .IP "1." 4 The name of the field for which terms are provided. .RE .RS 4 .Sp (That is the only type used.) .RE .IP "\(bu" 4 \&\f(CW\*(C`terms\*(C'\fR is a \f(CW\*(C`Net::Z3950::FacetTerms\*(C'\fR array. .IP "\(bu" 4 This is an array of \f(CW\*(C`Net::Z3950::FacetTerm\*(C'\fR objects. .IP "\(bu" 4 Each of these is an object with two members, \f(CW\*(C`term\*(C'\fR and \f(CW\*(C`count\*(C'\fR. The first of these is a string containing one of the facet terms, and the second is an integer indicating how many times it occurs in the records that were found by the search. .PP The example SimpleServer applicaation server \f(CW\*(C`ztest.pl\*(C'\fR includes code that shows how to examine the \s-1INPUTFACETS\s0 data structure and create the \s-1OUTPUTFACETS\s0 structure. .SS "Present handler" .IX Subsection "Present handler" The presence of a present handler in a SimpleServer front-end is optional. Each time a client wishes to retrieve records, the present service is called. The present service allows the origin to request a certain number of records retrieved from a given result set. When the present handler is called, the front-end server should prepare a result set for fetching. In practice, this means to get access to the data from the backend database and store the data in a temporary fashion for fast and efficient fetching. The present handler does *not* fetch anything. This task is taken care of by the fetch handler, which will be called the correct number of times by the \s-1YAZ\s0 library. More about this below. If no present handler is implemented in the front-end, the \s-1YAZ\s0 toolkit will take care of a minimum of preparations itself. This default present handler is sufficient in many situations, where only a small amount of records are expected to be retrieved. If on the other hand, large result sets are likely to occur, the implementation of a reasonable present handler can gain performance significantly. .PP The information exchanged between client and present handle is: .PP .Vb 2 \& $args = { \& ## Client/server request: \& \& GHANDLE => $obj ## Global handle specified at creation \& HANDLE => ref, ## Reference to datastructure \& SETNAME => "id", ## Result set ID \& START => xxx, ## Start position \& COMP => "", ## Desired record composition \& NUMBER => yyy, ## Number of requested records \& \& \& ## Response parameters: \& \& HITS => zzz, ## Number of returned records \& ERR_CODE => 0, ## Error code \& ERR_STR => "" ## Error message \& }; .Ve .SS "Fetch handler" .IX Subsection "Fetch handler" The fetch handler is asked to retrieve a \s-1SINGLE\s0 record from a given result set (the front-end server will automatically call the fetch handler as many times as required). .PP The parameters exchanged between the server and the fetch handler are: .PP .Vb 2 \& $args = { \& ## Client/server request: \& \& GHANDLE => $obj ## Global handle specified at creation \& HANDLE => ref ## Reference to data structure \& SETNAME => "id" ## ID of the requested result set \& OFFSET => nnn ## Record offset number \& REQ_FORM => "n.m.k.l"## Client requested format OID \& COMP => "xyz" ## Formatting instructions \& SCHEMA => "abc" ## Requested schema, if any \& \& ## Handler response: \& \& RECORD => "" ## Record string \& BASENAME => "" ## Origin of returned record \& LAST => 0 ## Last record in set? \& ERR_CODE => 0 ## Error code \& ERR_STR => "" ## Error string \& SUR_FLAG => 0 ## Surrogate diagnostic flag \& REP_FORM => "n.m.k.l"## Provided format OID \& SCHEMA => "abc" ## Provided schema, if any \& }; .Ve .PP The \s-1REP_FORM\s0 value has by default the \s-1REQ_FORM\s0 value, but can be set to something different if the handler desires. The \s-1BASENAME\s0 value should contain the name of the database from where the returned record originates. The \s-1ERR_CODE\s0 and \s-1ERR_STR\s0 works the same way they do in the search handler. If there is an error condition, the \s-1SUR_FLAG\s0 is used to indicate whether the error condition pertains to the record currently being retrieved, or whether it pertains to the operation as a whole (e.g. the client has specified a result set which does not exist.) .PP If you need to return \s-1USMARC\s0 records, you might want to have a look at the \s-1MARC\s0 module on \s-1CPAN,\s0 if you don't already have a way of generating these. .PP \&\s-1NOTE:\s0 The record offset is 1\-indexed, so 1 is the offset of the first record in the set. .SS "Scan handler" .IX Subsection "Scan handler" A full featured Z39.50 server should support scan (or in some literature browse). The client specifies a starting term of the scan, and the server should return an ordered list of specified length consisting of terms actually occurring in the data base. Each of these terms should be close to or equal to the term originally specified. The quality of scan compared to simple search is a guarantee of hits. It is simply like browsing through an index of a book, you always find something! The parameters exchanged are: .PP .Vb 2 \& $args = { \& ## Client request \& \& GHANDLE => $obj, ## Global handle specified at creation \& HANDLE => $ref, ## Reference to data structure \& DATABASES => ["xxx"], ## Reference to a list of data\- \& ## bases to search \& TERM => \*(Aqstart\*(Aq, ## The start term \& RPN => $obj, ## Reference to a Net::Z3950::RPN::Term \& \& NUMBER => xx, ## Number of requested terms \& POS => yy, ## Position of starting point \& ## within returned list \& STEP => 0, ## Step size \& \& ## Server response \& \& ERR_CODE => 0, ## Error code \& ERR_STR => \*(Aq\*(Aq, ## Diagnostic message \& NUMBER => zz, ## Number of returned terms \& STATUS => $status, ## ScanSuccess/ScanFailure \& ENTRIES => $entries ## Referenced list of terms \& }; .Ve .PP where the term list is returned by reference in the scalar \f(CW$entries\fR, which should point at a data structure of this kind, .PP .Vb 3 \& my $entries = [ \& { TERM => \*(Aqenergy\*(Aq, \& OCCURRENCE => 5 }, \& \& { TERM => \*(Aqenergy density\*(Aq, \& OCCURRENCE => 6, }, \& \& { TERM => \*(Aqenergy flow\*(Aq, \& OCCURRENCE => 3 }, \& \& ... \& \& ... \& ]; .Ve .PP The \f(CW$status\fR flag is only meaningful after a successful scan, and should be assigned one of two values: .PP .Vb 2 \& Net::Z3950::SimpleServer::ScanSuccess Full success (default) \& Net::Z3950::SimpleServer::ScanPartial Fewer terms returned than requested .Ve .PP The \s-1STEP\s0 member contains the requested number of entries in the term-list between two adjacent entries in the response. .PP A better alternative to the \s-1TERM\s0 member is the the \s-1RPN\s0 member, which is a reference to a Net::Z3950::RPN::Term object representing the scan clause. The structure of that object is the same as for Term objects included as part of the \s-1RPN\s0 tree passed to search handlers. This is more useful than the simple \s-1TERM\s0 because it includes attributes (e.g. access points associated with the term), which are discarded by the \s-1TERM\s0 element. .SS "Close handler" .IX Subsection "Close handler" The argument hash received by the close handler has two elements only: .PP .Vb 2 \& $args = { \& ## Server provides: \& \& GHANDLE => $obj ## Global handle specified at creation \& HANDLE => ref ## Reference to data structure \& }; .Ve .PP What ever data structure the \s-1HANDLE\s0 value points at goes out of scope after this call. If you need to close down a connection to your server or something similar, this is the place to do it. .SS "Explain handler" .IX Subsection "Explain handler" The argument hash received by the explain handler has the following elements: .PP .Vb 5 \& $args = { \& ## Request parameters: \& GHANDLE => $obj, # Global handle specified at creation \& HANDLE => ref, # Reference to data structure \& DATABASE => $dbname, # Name of database to be explained \& \& ## Response parameters: \& EXPLAIN => $zeerex # ZeeRex record for specified database \& }; .Ve .PP The handler should return a string containing the ZeeRex \s-1XML\s0 that describes that nominated database. .SS "Delete handler" .IX Subsection "Delete handler" The argument hash received by the delete handler has the following elements: .PP .Vb 5 \& $args = { \& ## Client request: \& GHANDLE => $obj, ## Global handle specified at creation \& HANDLE => ref, ## Reference to data structure \& SETNAME => "id", ## Result set ID \& \& ## Server response: \& STATUS => 0 ## Deletion status \& }; .Ve .PP The \s-1SETNAME\s0 element of the argument hash may or may not be defined. If it is, then \s-1SETNAME\s0 is the name of a result set to be deleted; if not, then all result-sets associated with the current session should be deleted. In either case, the callback function should report on success or failure by setting the \s-1STATUS\s0 element either to zero, on success, or to an integer from 1 to 10, to indicate one of the ten possible failure codes described in section 3.2.4.1.4 of the Z39.50 standard \*(-- see http://www.loc.gov/z3950/agency/markup/05.html#Delete\-list\-statuses1 .SS "Sort handler" .IX Subsection "Sort handler" The argument hash received by the sort handler has the following elements: .PP .Vb 7 \& $args = { \& ## Client request: \& GHANDLE => $obj, ## Global handle specified at creation \& HANDLE => ref, ## Reference to data structure \& INPUT => [ a, b ... ], ## Names of result\-sets to sort \& OUTPUT => "name", ## Name of result\-set to sort into \& SEQUENCE ## Sort specification: see below \& \& ## Server response: \& STATUS => 0, ## Success, Partial or Failure \& ERR_CODE => 0, ## Error code \& ERR_STR => \*(Aq\*(Aq, ## Diagnostic message \& \& }; .Ve .PP The \s-1SEQUENCE\s0 element is a reference to an array, each element of which is a hash representing a sort key. Each hash contains the following elements: .IP "\s-1RELATION\s0" 4 .IX Item "RELATION" 0 for an ascending sort, 1 for descending, 3 for ascending by frequency, or 4 for descending by frequency. .IP "\s-1CASE\s0" 4 .IX Item "CASE" 0 for a case-sensitive sort, 1 for case-insensitive .IP "\s-1MISSING\s0" 4 .IX Item "MISSING" How to respond if one or more records in the set to be sorted are missing the fields indicated in the sort specification. 1 to abort the sort, 2 to use a \*(L"null value\*(R", 3 if a value is provided to use in place of the missing data (although in the latter case, the actual value to use is currently not made available, so this is useless). .PP And one or other of the following: .IP "\s-1SORTFIELD\s0" 4 .IX Item "SORTFIELD" A string indicating the field to be sorted, which the server may interpret as it sees fit (presumably by an out-of-band agreement with the client). .IP "\s-1ELEMENTSPEC_TYPE\s0 and \s-1ELEMENTSPEC_VALUE\s0" 4 .IX Item "ELEMENTSPEC_TYPE and ELEMENTSPEC_VALUE" I have no idea what this is. .IP "\s-1ATTRSET\s0 and \s-1SORT_ATTR\s0" 4 .IX Item "ATTRSET and SORT_ATTR" \&\s-1ATTRSET\s0 is the attribute set from which the attributes are taken, and \&\s-1SORT_ATTR\s0 is a reference to an array containing the attributes themselves. Each attribute is represented by (are you following this carefully?) yet another hash, this one containing the elements \&\s-1ATTR_TYPE\s0 and \s-1ATTR_VALUE:\s0 for example, type=1 and value=4 in the \s-1BIB\-1\s0 attribute set would indicate access-point 4 which is title, so that a sort of title is requested. .PP Precisely why all of the above is so is not clear, but goes some way to explain why, in the Z39.50 world, the developers of the standard are not so much worshiped as blamed. .PP The backend function should set \s-1STATUS\s0 to 0 on success, 1 for \*(L"partial success\*(R" (don't ask) or 2 on failure, in which case \s-1ERR_CODE\s0 and \&\s-1ERR_STR\s0 should be set. .SS "Support for \s-1SRU\s0 and \s-1SRW\s0" .IX Subsection "Support for SRU and SRW" Since release 1.0, SimpleServer includes support for serving the \s-1SRU\s0 and \s-1SRW\s0 protocols as well as Z39.50. These ``web\-friendly'' protocols enable similar functionality to that of Z39.50, but by means of rich URLs in the case of \s-1SRU,\s0 and a SOAP-based web-service in the case of \&\s-1SRW.\s0 These protocols are described at http://www.loc.gov/standards/sru/ .PP In order to serve these protocols from a SimpleServer-based application, it is necessary to launch the application with a \s-1YAZ\s0 Generic Frontend Server (\s-1GFS\s0) configuration file, which can be specified using the command-line argument \f(CW\*(C`\-f\*(C'\fR \fIfilename\fR. A minimal configuration file looks like this: .PP .Vb 5 \& \& \& pqf.properties \& \& .Ve .PP This file specifies only that \f(CW\*(C`pqf.properties\*(C'\fR should be used to translate the \s-1CQL\s0 queries of \s-1SRU\s0 and \s-1SRW\s0 into corresponding Z39.50 Type\-1 queries. For more information about \s-1YAZ GFS\s0 configuration, including how to specify an Explain record, see the \fIVirtual Hosts\fR section of the \s-1YAZ\s0 manual at http://www.indexdata.com/yaz/doc/server.vhosts.html .PP The mapping of \s-1CQL\s0 queries into Z39.50 Type\-1 queries is specified by a file that indicates which \s-1BIB\-1\s0 attributes should be generated for each \s-1CQL\s0 index, relation, modifiers, etc. A typical section of this file looks like this: .PP .Vb 5 \& index.dc.title = 1=4 \& index.dc.subject = 1=21 \& index.dc.creator = 1=1003 \& relation.< = 2=1 \& relation.le = 2=2 .Ve .PP This file specifies the \s-1BIB\-1\s0 access points (type=1) for the Dublin Core indexes \f(CW\*(C`title\*(C'\fR, \f(CW\*(C`subject\*(C'\fR and \f(CW\*(C`creator\*(C'\fR, and the \s-1BIB\-1\s0 relations (type=2) corresponding to the \s-1CQL\s0 relations \f(CW\*(C`<\*(C'\fR and \&\f(CW\*(C`<=\*(C'\fR. For more information about the format of this file, see the \fI\s-1CQL\s0\fR section of the \s-1YAZ\s0 manual at http://www.indexdata.com/yaz/doc/tools.html#cql .PP The \s-1YAZ\s0 distribution includes a sample CQL-to-PQF mapping configuration file called \f(CW\*(C`pqf.properties\*(C'\fR; this is sufficient for many applications, and a good base to work from for most others. .PP If a SimpleServer-based application is run without this SRU-specific configuration, it can still serve \s-1SRU\s0; however, \s-1CQL\s0 queries will not be translated, but passed straight through to the search-handler function, as the \f(CW\*(C`CQL\*(C'\fR member of the parameters hash. It is then the responsibility of the back-end application to parse and handle the \s-1CQL\s0 query, which is most easily done using Ed Summers' fine \f(CW\*(C`CQL::Parser\*(C'\fR module, available from \s-1CPAN\s0 at http://search.cpan.org/~esummers/CQL\-Parser/ .SH "AUTHORS" .IX Header "AUTHORS" Anders Sønderberg (sondberg@indexdata.dk), Sebastian Hammer (quinn@indexdata.dk), Mike Taylor (indexdata.com). .SH "COPYRIGHT AND LICENCE" .IX Header "COPYRIGHT AND LICENCE" Copyright (C) 2000\-2016 by Index Data. .PP 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. .SH "SEE ALSO" .IX Header "SEE ALSO" Any Perl module which is useful for accessing the data source of your choice.