source: tags/arb-6.0.1/PERL2ARB/DOC.html

ARB_DB

Basic idea:

        All data is stored hierarchically in database elements.

        A database element is a small structure which stores:
                - key
                - type  (integer/string...)
                - it's value
                - last modification time
                - access rights
                ...

        A value itself might be a set of database elements.

        There are 10 basic data types:
        Type            C/C++ enum      PERL_NAME
        ----------------------------------------------------------------
        String          GB_STRING       STRING  // Null terminated string
        Integer         GB_INT          INT     // 32 bit integer
        Float           GB_FLOAT        FLOAT   // real number
        BitString       GB_BITS         BITS    // any bitstring
        Integer String  GB_INTS         INTS    // array of integer
        Container       GB_DB           CONTAINER // a set of other elements


        ****************************** Example 1 ***************

        Let's say we want to store the following key value pairs in the
        database:
                name    niels
                tel     37543345
                sex     male
                age     40

        So all we have to do is to create 4 database elements of type
        STRING and store the data into it:

                $gb_main = ARB::open("new_db.arb","wc");        // create new db
                                // we are operating
                                // in a multi user env., so we have to
                                // get exclusive rights to the server:
                ARB::begin_transaction($gb_main);
                                // create a dbelem key = "name"
                                //                      type = "STRING"
                $gb_name = ARB::create($gb_main,"name","STRING");
                                // and store a value in the dbelem
                $error = ARB:write_string($gb_name,"niels");
                        ...
                        ...
                ARB:commit_transaction($gb_main);       // everything is ok
                $error = ARB::save($gb_main,"new_db.arb", "a"); // save in ascii format

        ***************************** END 1 *********************


        What has been done:

                The first argument of nearly all ARB-Database (ARBDB) functions
                is an existing database element.
                You may change or read this element or use it to find or
                create other elements.

                First we create a new database "new_db.arb".
                ARB::open returns the root element of the database.
                Before we can actually read or write to it we have to
                get exclusive rights by calling
                        GB_begin_transaction( root_element_of_database );
                To make all changes to the database persistent we have
                to call GB_commit_transaction, or if we want to undo all
                recent changes GB_abort_transaction.
                Because the root node of the database is always a container
                we can simply add new items to it.


        ****************************** Example 2 ***************

        We have the same situation as in Example 1 but we want to store
        the name, tel .. of different persons in the database.

        So we simply store the person's data not in the root container,
        but in a person container.

                $gb_main = ....
                ARB::begin_transaction($gb_main);

                for all persons do {
                        $gb_person = ARB::create_container($gb_main,"person");
                        $gb_name = ARB::create($gb_person,"name","STRING");
                        $error = ARB:write_string($gb_name,"name of p");
                        if ($error) .....
                        $gb_tel = ARB::create($gb_person,"tel", STRING);
                        $error = ARB:write_string($gb_tel,"telnr of person");
                }
                commit and save

        ******************************* END 2 ***************************

        What's new in the last example:

                We created sub containers for each person. All this
                have the key 'person', so in this case the key is really
                useless. Some people might think that it would be much
                better to give each container the name of the person.
                But that would limit you to search for only one field.
                So we decided not to index the keys of the database
                elements but their values. So you should not use the
                key for indexing.


Searching the database:
        There are three main ways to find your data:

                1. Use the key of the elements:
                        This is good if all your keys are unique in
                        a container and if there are only a few elements
                        in a container.

                2. Use the value of the elements:
                        This works like grep in a filesystem. Go through
                        all elements and  inspect the value.
                        This can be indexed, and is therefor much faster
                        and more flexible than the search by key method.

                3. Walk through the database by hand:
                        All elements within one container are stored as
                        a linked list. A small loop allows you to create
                        any user defined query

        All searching is done by two functions:
                find and search
        Both functions start the search at a user defined database elem
        (first argument).

        ARB::search is used, if all keys in a container are unique.
        example:

        $gb_searched = ARB:search($gb_start,"key1","none");
                searches in the container $gb_start for an element with
                the key 'key1'

        $gb_searched = ARB:search($gb_start,"key1/key2","none");
                searches a container $gb_h with key 'key1' in $gb_start
                and if found continues searching in $gb_h for an element
                with key 'key2'

        The last parameter enables ARB::search to create an element if it
        has not found any. To do this simply enter the type of the new
        element as the third argument. This is really usefull, if you want
        to store information in an existing database and you do not know
        whether an element exists already or not.


        ARB::find is used if not all keys are unique

        Like ARB::search it starts the search at a given element.
        It's basic syntax looks like this:

        ARB::find($gb_start_point, "[opt key]", "[opt value]", "mode");
                where mode can be:      "this"
                                        "down"
                                        "down_2"
                                        "this_next"
                                        "down_next"

        if "[opt key]" != "" than look only for items with that key
        if "[opt value]" != "" than return only those items which value
                        mach the "[opt value]"
                Any '*' maches any number of characters
                Any '?' maches exactly one character
                the rest maches itself

        If opt key is the searched key and opt value == "" and mode ==
        "down" than ARB::find will behave like ARB::search.

        mode indicates the direction of the search:
        "down"   means that $gb_start_point is a container and it
                looks for an element in that container
        "down_2" means that $gb_start_point is a container and all its
                elements are containers and it looks for elements in
                the subcontainers of $gb_start_point
        "this"  forces ARB::search to look for a brother
                of $gb_start_point.
        "this_next" continues a search started by mode == "down",
                The first parameter should be the last hit
        "down_next" continues a search started by mode == "down_2",
                The first parameter should be the father of the last hit.
                To get the father of an element call
                        ARB::get_father($gb_elem);



        ****************************** Example 3 ***************
        Let's find Niels in our database from example 2
        and print his data on the screen


        ....
                        // find an element which holds niels name
        $gb_niels_name = ARB::find($gb_main,"name","niels","down_2");
                        // We want the container for niels not just his name
        $gb_niels = ARB::get_father($gb_niels_name);
                        // lets loop through everything
        $gb_any = ARB::find($gb_niels,"","",down_level);
        while ($gb_any) {
                        // We know that we have only strings, so this is
save
                        // Just read the value
                $value = ARB::read_string($gb_any);
                        // and we need the key
                $key = ARB::read_key($gb_any);
                print "$key:    $value\n";
                        // get the next element
                $gb_any = ARB::find($gb_any,"","","this_next");
        }
        ...


***************************** All the functions ***************

Now the rest is really trivial: only a lot of functions

        Some name conventions:
                $gb_xxx indicates are variable which is a database
                        element
                $gb_cxxx is any container
                $gb_main is always the root element
                $error is an error string



$gb_main = ARB::open("path of existing or new database.arb",flags)
        if "path of existing or new database.arb" contains a ':'
        character, then ARB looks for a server instead of a file.
                path syntax:    hostname:tcpnr          // network mode
                                :path_of_unix_socket    // unix socket
                                :                       // default socket

        flags is a string of characters:
                r               read existing database
                w               database should be writeable
                c               create a new one if read failed
                -> r            reads a database
                -> rwc          reads or creates a database
                -> wc           always creates a new one


$error = ARB::save($gb_main,"path of the database",mode)
        mode
                a               ascii format
                b               binary format
        Only if you have opened a database on a file you are allowed to
        save it, otherwise the server has to do it.
        You may not change the path of the database, it is used
        for security. If you want to save the database to a new
        file use:

$error = ARB::save_as($gb_main,"path of the database",mode)


$error = ARB::save_quick($gb_main,"existing path of the database");
        Save all changes to a file "xxxx.quickX" where X is an
        autoincremented number between 0 and 7

$error = ARB::save_quick_as($gb_main,"new path");
        Fake an existing database by create a symbolic link and
        then call ARB::save_quick

$error = ARB::close($gb_main);
        You should be polite to your server and say good bye, so
        please call this function just before you exit.
        Nothing serious will happen if you forget to call it.


$error = ARB::begin_transaction($gb_main);
        Get the exclusive read and write rights from the server
$error = ARB::abort_transaction($gb_main);
        Undo everything since the last begin_transaction
$error = ARB::commit_transaction($gb_main);
        Write all data to the server and give the database rights
        back to other users

$error = ARB::push_transaction($gb_main);
        Increments an internal counter. If the counter was previously
        0 then calls begin_transaction. This is usefull when working
        in a subroutine and not knowing whether your calling function
        had opened a transaction already.
$error = ARB::pop_transaction($gb_main);
        Decrements the internal counter. If the counter gets zero,
        commit a transaction.


****************** Now the following functions assume that you have
        began a transaction ***************************

*************************** error handling ********************
Most of the functions return an optional error string if there have
been a problem. If a function do not return a error string but
for example a database element, you may get the error string by
        calling ARB::get_error()

example:
        $gb_main = ARB::open("Idonotexist","rw");
        if (! $gb_main ) $error = ARB::get_error();

**************************** find and search entries ***********

$gb_xxx = ARB::search($gb_start_search_point,"path/in/the/database",
                "TYPE_OF_ELEMENT_YOU_WANT_CREATE/none"
        search a database element if all keys are unique

$gb_xxx = ARB::find($gb_start_search_point, "[key]", "[value]",
        "search_mode"


************************** create new entries ***************

$gb_new_entry = ARB::create($gb_cxx, "key", "type");
        creates a new element of type "type" within $gb_cxx

$gb_new_container = ARB::create_container($gb_cxx,"key");
        create a new container within $gb_cxx

************************* read entries *******************
        // simple types
$val = ARB::read_byte($gb_xxx);
$val = ARB::read_int($gb_xxx);
$val = ARB::read_float($gb_xxx);
        // array types
$val = ARB::read_string($gb_xxx);       // read the value
$val = ARB::read_bytes($gb_xxx);        // may contain \0 characters
$val = ARB::read_ints_using_index($gb_xx, "index");
                                        // read the integer #index of an
                                        // integer array
$val = ARB::read_floats_using_index($gb_xxx, "index");

$val = ARB::read_count($gb_xxx);        // get the size of the array

$val = ARB::read_as_string($gb_xxx);    // read and convert to string

$val = ARB::read_bits($gb_xxx,char_0,char_1);
        convert a bit array into a string,
        a '0' will be converted into char_0
        a '1' into char_1

        eg: ARB:read_bits($gb_xxx, "-", "+" ); returns a '-' '+' string


************************* write entries *******************

$error = ARB::write_int($gb_xxx, "value");      // write the value
$error = ARB::write_float($gb_xxx, "value");    // write the value
$error = ARB::write_byte($gb_xxx, "value");     // write the value

$error = ARB::write_bytes($gb_xxx, "value", len);// write array of bytes
$error = ARB::write_string($gb_xxx, "value");   // write the value
$error = ARB::write_bits($gb_xxx, "value", char_0); // convert a string
                                // into bitarray, all characters !=
                                // char_0 will converted to 1 else 0

$error = ARB::write_as_string($gb_xxx); try to interpret the value and
                                // convert it automatically to the right
                                // format

If you write to an element and you do not change the value,
the element thinks, that you have done nothing, and no
element pending events are called, and the modification time is not
changed. If you want to force to change the element, call

$error = ARB::touch($gb_xxx);

******************************* etc entries ****************

$error = ARB::delete($gb_xxx);
        deletes an element or a container and it's subelements

$error = ARB::copy($gb_destination, $gb_source);
        copy's the value from source to destination.
        does not create a new element.
        the type of $gb_destination must be the type of $gb_source
        if type == "CONTAINER" than all subelements are copied

************************ security levels **********************

each database element has three security levels:
        read write and delete
each level's value is between 0 and 7

$val = ARB::read_security_read($gb_xxx);
$val = ARB::read_security_write($gb_xxx);
$val = ARB::read_security_delete($gb_xxx);

$error = ARB::write_security_read($gb_xxx, "val");
$error = ARB::write_security_write($gb_xxx, "val");
$error = ARB::write_security_delete($gb_xxx, "val");

to change any element, the users security level must be greater or
equal the elements level. To change the users level call:

$error        = ARB::change_my_security($gb_main,"level","passwd");
        passwd is not in use yet


*********************** additional element information ***********

$type = ARB::read_type($gb_xxx);
        gets the type of a database elem: "INT" "STRING" "CONTAINER" ....

$key = ARB::read_key($gb_xxx);
        read the key of a database elem:

$clock = ARB::read_clock($gb_xxx);
        gets the last modification time of an entry.
        The modification time of a container is always greater or equal
        then the modification time of it's subelements.
        The clock counts transactions, not seconds


$error = ARB::set_temporary($gb_xxx);
        Marks a field in the database as a temporary field.
        That means that this field is never saved to a file.
$error = ARB::clear_temporary($gb_xxx);
        Clears tmp flag

$error = ARB::write_flag($gb_xxx, bool);
        Sets or clears a flag in the database,
        There are functions to quickly find all flagged == marked
        entries

$gb_xxx = ARB::first_marked($gb_cxx);
        finds the first flagged element in a container

$gb_xxx = ARB::next_marked($gb_xxx);
        gets the next flagged item

$count = ARB::number_of_marked_subentries($gb_cxxx);
        adds all flags of direct subentries within $gb_cxxx

$error = ARB::write_usr_public($gb_xxx, value);
        Each element has 8 free public bits
        public means that all clients share the same bits

$value = ARB::read_usr_public($gb_xxx);


$error = ARB::write_usr_private($gb_xxx, value);
        Each element has 8 free private bits
        private means each database client has it's own bits
$value = ARB::read_usr_private($gb_xxx);


************************** ETC ************************

$error = ARB::release($gb_xxx);
        By default all clients cache all data which has been searched,
        read or modified.
        If you want to get rid of some cached items you may call
        ARB::release, which frees all data below $gb_xxx.
        Warning: All database elements, which are a subentry of $gb_xxx
        will be temporary lost. You have to search or find them again.


$error = ARB::add_callback($gb_xxx, function_name, clientdata);
        Adds a callback to a database element.
        Every time you call begin_transaction and any other client
        has changed this database element, your function_name is called
        Every time you call commit_transaction and you have made
        changed to this item, your function_name is called,

        function_name is a function with the following parameters:

        func($gb_changed_element, clientdata, "DELETED/CHANGED"
                A "DELETED" value in the third argument means that
                the element had been deleted
                A "CHANGED" value indicate only a change.

$error = ARB::remove_callback($gb_xxx, function_name);
        remove a callback


$error = ARB::create_index($gb_cxx, "key", estimated_size);
        If you call ARB::find with mode "down_2" or "this_next"
        very often on a huge database you may create an index.
        estimated_size is the estimated number of items which should
        be indexed.
        In the current version we are using a hash mechanism to index
        the elements. Only strings can be indexed.

$error = ARB::undo($gb_main, "UNDO"/"REDO");
        undo oder redo the database.
        Should not be called within a running transaction

$info = ARB::undo_info($gb_main, "UNDO"/"REDO");
        Should give you a short information about the next undo/redo

$error = ARB::set_undo_mem($gb_main, size_in_bytes);
        sets the amount of memory used to store undo values

$time = ARB::last_saved_clock($gb_main);
        transaction number when the database was last saved
        Can only be called from the server program

$time = ARB::last_saved_time($gb_main);
        the same but in seconds after 1 Jan 0:00 1970

$error = ARB::set_cache_size($gb_main, "size_in_bytes");
        ARB uses datacompression for long strings. If some strings
        are used very intensely the program may slow down.
        Therefor a small cache is used and it's size can be set
        by this function. If you are working with sequences, a value
        of 1 or 2 meg seems reasonable


$error = ARB::check_key("key");
        checks "key" is a valid key

************************* Creating a server ******************

$error = ARB::sopen("socketid",timeout_in_millisec, $gb_main);
        serves $gb_main for other clients.
        syntax of "socketid":
                host:tcpnr
                :/path/of/unix/socket
                :                       // default unix socket

        prepares the database to be served. timeout is not used now
        but later in:

$error = ARB::accept_calls($gb_main);
        Watch your socket timeout_in_millisec for any clients, who need
        help

$error = ARB::shutdown($gb_main);
        shutdown the server

$clients = ARB::read_clients($gb_main)
        Get the number of clients using this server.
        if $clients == -1 than I'm a client no server
        So this can be used to check wether I'm a client or server