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4.2
Interpretive Transformer Approach
An interpretive transformer accepts a source definition, a target definition, and a
mapping definition, and then maps the stored data from the source to the target
database (Lochovsky and Tsichritzis 1982 ) as shown in Fig. 4.1 .
Suppose that the database of a source nonrelational schema S s is mapped to a
target relational schema S t . There are three distinct processes in this approach. One
process accesses the source data (reading). Another process performs logical trans-
formations on the data to place it into an internal form. A third process creates the
target data (writing).
For example, Fry et al ( 1978 ) described a method that uses two specialized lan-
guages, the Stored Data Definition Language (SDDL) and the Translation Defini-
tion Language (TDL), to define the structure of the two databases and the source to
target translation parameters. Using these definitions, a series of programs (refer to
Fig. 4.2 ) are used to perform the data conversion process.
Definitions of
source, target,
and mapping
Interpretive
transformer
source
target
Fig. 4.1 Interpretive transformer
Description
of Source
Description
of Ta rget
Restructuring
Source
Converter
Ta rget
converter
Source
Form
normal
Form
normal
form
Target
form
Restructure
Fig. 4.2 The general model for data translator
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