Create an abstract database object.
The return value is the new abstract database object.

Add a real number to a record.
`key' specifies the key.
`num' specifies the additional value.
If successful, the return value is the summation value, else, it is `nil'.
If the corresponding record exists, the value is treated as a real number and is added to. If no record corresponds, a new record of the additional value is stored. Because records are stored in binary format, they should be processed with the `unpack' method with the `d' operator after retrieval.

Add an integer to a record.
`key' specifies the key.
`num' specifies the additional value.
If successful, the return value is the summation value, else, it is `nil'.
If the corresponding record exists, the value is treated as an integer and is added to. If no record corresponds, a new record of the additional value is stored. Because records are stored in binary format, they should be processed with the `unpack' method with the `i' operator after retrieval.

Close the database.
If successful, the return value is true, else, it is false.
Update of a database is assured to be written when the database is closed. If a writer opens a database but does not close it appropriately, the database will be broken.

Copy the database file.
`path' specifies the path of the destination file. If it begins with `@', the trailing substring is executed as a command line.
If successful, the return value is true, else, it is false. False is returned if the executed command returns non-zero code.
The database file is assured to be kept synchronized and not modified while the copying or executing operation is in progress. So, this method is useful to create a backup file of the database file.

Get forward matching keys.
`prefix' specifies the prefix of the corresponding keys.
`max' specifies the maximum number of keys to be fetched. If it is not defined or negative, no limit is specified.
The return value is a list object of the keys of the corresponding records. This method does never fail. It returns an empty list even if no record corresponds.
Note that this method may be very slow because every key in the database is scanned.

Retrieve a record.
`key' specifies the key.
If successful, the return value is the value of the corresponding record. `nil' is returned if no record corresponds.

Initialize the iterator.
If successful, the return value is true, else, it is false.
The iterator is used in order to access the key of every record stored in a database.

Get the next key of the iterator.
If successful, the return value is the next key, else, it is `nil'. `nil' is returned when no record is to be get out of the iterator.
It is possible to access every record by iteration of calling this method. It is allowed to update or remove records whose keys are fetched while the iteration. However, it is not assured if updating the database is occurred while the iteration. Besides, the order of this traversal access method is arbitrary, so it is not assured that the order of storing matches the one of the traversal access.

Call a versatile function for miscellaneous operations.
`name' specifies the name of the function.
`args' specifies an array of arguments. If it is not defined, no argument is specified.
If successful, the return value is an array of the result. `nil' is returned on failure.

Open a database.
`name' specifies the name of the database. If it is “*”, the database will be an on-memory hash database. If it is “+”, the database will be an on-memory tree database. If its suffix is “.tch”, the database will be a hash database. If its suffix is “.tcb”, the database will be a B+ tree database. If its suffix is “.tcf”, the database will be a fixed-length database. If its suffix is “.tct”, the database will be a table database. Otherwise, this method fails. Tuning parameters can trail the name, separated by “#”. Each parameter is composed of the name and the value, separated by “=”. On-memory hash database supports “bnum”, “capnum”, and “capsiz”. On-memory tree database supports “capnum” and “capsiz”. Hash database supports “mode”, “bnum”, “apow”, “fpow”, “opts”, “rcnum”, and “xmsiz”. B+ tree database supports “mode”, “lmemb”, “nmemb”, “bnum”, “apow”, “fpow”, “opts”, “lcnum”, “ncnum”, and “xmsiz”. Fixed-length database supports “mode”, “width”, and “limsiz”. Table database supports “mode”, “bnum”, “apow”, “fpow”, “opts”, “rcnum”, “lcnum”, “ncnum”, “xmsiz”, and “idx”.
If successful, the return value is true, else, it is false.
The tuning parameter “capnum” specifies the capacity number of records. “capsiz” specifies the capacity size of using memory. Records spilled the capacity are removed by the storing order. “mode” can contain “w” of writer, “r” of reader, “c” of creating, “t” of truncating, “e” of no locking, and “f” of non-blocking lock. The default mode is relevant to “wc”. “opts” can contains “l” of large option, “d” of Deflate option, “b” of BZIP2 option, and “t” of TCBS option. “idx” specifies the column name of an index and its type separated by “:”. For example, “casket.tch#bnum=1000000opts=ld” means that the name of the database file is “casket.tch“, and the bucket number is 1000000, and the options are large and Deflate.

Optimize the storage.
`params' specifies the string of the tuning parameters, which works as with the tuning of parameters the method `open'. If it is not defined, it is not used.
If successful, the return value is true, else, it is false.

Remove a record.
`key' specifies the key.
If successful, the return value is true, else, it is false.

Get the path of the database file.
The return value is the path of the database file or `nil' if the object does not connect to any database instance. “*” stands for on-memory hash database. “+” stands for on-memory tree database.

Store a record.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If a record with the same key exists in the database, it is overwritten.

Concatenate a value at the end of the existing record.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If there is no corresponding record, a new record is created.

Store a new record.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If a record with the same key exists in the database, this method has no effect.

Get the number of records.
The return value is the number of records or 0 if the object does not connect to any database instance.

Get the size of the database.
The return value is the size of the database or 0 if the object does not connect to any database instance.

Synchronize updated contents with the file and the device.
If successful, the return value is true, else, it is false.
This method is useful when another process connects the same database file.

Abort the transaction.
If successful, the return value is true, else, it is false.
Update in the transaction is discarded when it is aborted. The state of the database is rollbacked to before transaction.

Begin the transaction.
If successful, the return value is true, else, it is false.
The database is locked by the thread while the transaction so that only one transaction can be activated with a database object at the same time. Thus, the serializable isolation level is assumed if every database operation is performed in the transaction. All updated regions are kept track of by write ahead logging while the transaction. If the database is closed during transaction, the transaction is aborted implicitly.

Commit the transaction.
If successful, the return value is true, else, it is false.
Update in the transaction is fixed when it is committed successfully.

Remove all records.
If successful, the return value is true, else, it is false.

Get the size of the value of a record.
`key' specifies the key.
If successful, the return value is the size of the value of the corresponding record, else, it is -1.