Tie::FieldVals 0.40

Tie::FieldVals is an array tie for a file of enhanced Field:Value data.

SYNOPSIS

use Tie::FieldVals;
use Tie::FieldVals::Row;

# tie the array
my @records;
my $recs_obj = tie @records, Tie::FieldVals, datafile=>$datafile;

# object methods
my @field_names = $recs_obj->field_names();

This is a Tie object to map the records in an enhanced Field:Value data file into an array. Each file has multiple records, each record has its values defined by a Field:Value pair, with the enhancements that (a) the Value part can extend over more than one line (because the Field names are predefined) and (b) Fields can have multiple values by repeating the Field:Value part for a given field.

Because of its use of the Tie::File module, access to each record is reasonably fast. The Tie::File module also ensures that (a) the whole file doesnt have to be read into memory (b) record changes are written to the file straight away (c) record changes dont require the whole file to be rewritten, just the part of the file after the change.

The advantage of this setup is that one can have useful data files which are plain text, human readable, human editable, and at the same time able to be accessed faster than using XML (I know, I wrote a version of my reporting software using XML data, and even the fastest XML parsers werent as fast as this setup, once there were a reasonable number of records). This also has advantages over a simpler setup where values are given one per line with no indication of what value belongs to what field; the problems with that is that it is harder to fix corrupted data by hand, and it is harder to add new fields, and one cant have multi-line data.

It is likewise better than a CSV (Comma-Separated Values) file, because again, with a CSV file, the data is positional and therefore harder to fix and harder to change, and again one cant have multi-line data.

This module is both better and worse than file-oriented databases like DB_File and its variants and extensions (such as MLDBM). This module does not require that each record have a unique key, and the fact that a DBM file is binary makes it not only less correctable, but also less portable. On the downside, this module isnt as fast.

Naturally, if ones data needs are more complex, it is probably better to use a fully-fledged database; this is oriented towards those who dont wish to have the overhead of setting up and maintaining a relational database server, and wish to use something more straightforward.

This comes bundled with other support modules, such as the Tie::FieldVals::Row module. The Tie::FieldVals::Select module is for selecting and sorting a sub-set from a Tie::FieldVals array, and the Tie::FieldVals::Join is a very simple method of joining two files on a common field.

This distribution includes the fv2xml script, which converts a Tie::FieldVals data file into an XML file, and xml2fv which converts an XML file into a Tie::FieldVals data file.