XML — Architecture, Tools, Techniques - Department of Computer ...

6.4 IBM alphaWorks XML Lightweight Extractor
XLE uses a DTD with source annotation (DTDSA). dtdsaCreator provides a GUI for editing.
The idea is that a DTD uniquely produces an XML based document if for every iteration with ?,
+, and * and for every selection with | and for PCDATA and CDATA it is known, how many and
which values will be inserted.
A DTDSA extends the DTD with value and binding specifications at the relevant positions. It
helps to load the DTD into dtdsaCreator, edit the necessary specifications, and store the result
as a DTDSA.
83
xle/hello.dtd
hello.dtdsa
Strictly speaking the DTD is not correct because as an external DTD it cannot be enclosed by
DOCTYPE. XLE, however, requires DOCTYPE to find the root element, i.e., XLE considers the
DTDSA more or less as a document that just consists of the prolog.
In this case there is no database access; therefore XLE can immediately be executed:
$ cd code/xle; alias run=`make run`
$ run XLE hello.dtdsa
Hello World
A value specification follows after a colon and must produce the value for a selection with |
and for PCDATA and CDATA. The following constructs can be used:
string "Hello World" string value.
parameter in0 command line argument following the
DTDSA.
field row.column value from the database: row is a variable
set by a binding specification, column is
an attribute name.
function field(table, column, row) value from the database: table selects
the table, column is the attribute name,
row is a variable set by a binding
specification.