http://fbclient.googlecode.com/files/DataDef.pdf の p107-p110
Using the EXTERNAL FILE option
The EXTERNAL FILE option creates a table for which the data resides in an external table
or file, rather than in the InterBase database. External files are ASCII text that can also be
read and manipulated by non-InterBase applications. In the syntax for CREATE TABLE, the
filespec that accompanies the EXTERNAL keyword is the fully qualified file specification for
the external data file. You can modify the external file outside of InterBase, since
InterBase accesses it only when needed.
Use the EXTERNAL FILE option to:
Import data from a flat external file in a known fixed-length format into a new or existing
InterBase table. This allows you to populate an InterBase table with data from an external
source. Many applications allow you to create an external file with fixed-length records.
SELECT from the external file as if it were a standard InterBase table.
Export data from an existing InterBase table to an external file. You can format the data
from the InterBase table into a fixed-length file that another application can use.