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$Id: step5.sdoc 1.7 2000/04/14 12:40:02 murata Exp $
Large modules are hard to maintain. STEP 5 introduces a mechanism for dividing a module into several pieces, which can be maintained easier.
Suppose that we rewrite a DTD containing 200 element types in RELAX. This size is fairly large, but is not uncommon. For each element type, RELAX needs an elementRule
and a tag
. If each elementRule
and tag
requires three lines, the total is 1200 lines. If we write extensive documentation, the total may become 3000 lines or even more. This size is too large to put in a single file.
Even DTD provides external parameter entities so as to divide large DTDs into modules and maintain each module independently. RELAX strongly requires some mechanism for dividing large modules.
include
elementIn RELAX, a module can reference to another module by the include
element. The include
element is replaced with the content of the referenced module.
Let us examine an example of include
. First, a module to be included is as below:
<module moduleVersion="1.2" relaxCoreVersion="1.0" targetNamespace="" xmlns="http://www.xml.gr.jp/xmlns/relaxCore"> <interface/> <elementRule role="bar" type="emptyString"/> <tag name="bar"/> </module>
This module contains an elementRule
and tag
for the element type bar
. The interface
element is empty. Suppose that this module is stored in bar.rlx
.
Next, a module which references to and includes this module is as below:
<module moduleVersion="1.2" relaxCoreVersion="1.0" targetNamespace="" xmlns="http://www.xml.gr.jp/xmlns/relaxCore"> <interface> <export label="foo"/> </interface> <elementRule role="foo"> <ref label="bar"/> </elementRule> <tag name="foo"/> <include moduleLocation="bar.rlx" /> </module>
This module contains an elementRule
and tag
for the element type foo
. The include
at the end of this this module references to bar.rlx
via the moduleLocation
attribute.
The include
element is replaced by the body of the referenced module, which the content of the module
element except the interface
element. In this example, replacement is done as below:
<module moduleVersion="1.2" relaxCoreVersion="1.0" targetNamespace="" xmlns="http://www.xml.gr.jp/xmlns/relaxCore"> <interface> <export label="foo"/> </interface> <elementRule role="foo"> <ref label="bar"/> </elementRule> <tag name="foo"/> <elementRule role="bar" type="emptyString"/> <tag name="bar"/> </module>
interface
elementsIn the above example, the interface
element of the referenced module is empty. Suppose that an export
element is supplied in the interface
element.
<module moduleVersion="1.2" relaxCoreVersion="1.0" targetNamespace="" xmlns="http://www.xml.gr.jp/xmlns/relaxCore"> <interface> <export label="bar"/> </interface> <elementRule role="bar" type="emptyString"/> <tag name="bar"/> </module>
In this case, the children of the interface
element in the referenced module are attached to the interface
element in the referencing module. In this example, the result of replacement is as below:
<module moduleVersion="1.2" relaxCoreVersion="1.0" targetNamespace="" xmlns="http://www.xml.gr.jp/xmlns/relaxCore"> <interface> <export label="foo"/> <export label="bar"/> </interface> <elementRule role="foo"> <ref label="bar"/> </elementRule> <tag name="foo"/> <elementRule role="bar" type="emptyString"/> <tag name="bar"/> </module>
STEP 5 makes it easy to maintain large modules. Enjoy and RELAX!