Date: 2004-04-26T05:49:44
Editor: HowardLewisShip <[EMAIL PROTECTED]>
Wiki: Jakarta HiveMind Wiki
Page: NotXMLProposal
URL: http://wiki.apache.org/jakarta-hivemind/NotXMLProposal
no comment
New Page:
= Problem Description =
HowardLewisShip, April 26 2004, 1-0-alpha-4
One of the tenets of !HiveMind is that deployment descriptors for J2EE are in
verbose XML.
And yet, the descriptors for HiveMind are themselves XML and can be quite
verbose.
Several people, especially ErikHatcher, have '''repeatedly''' pointed this out
to me.
As things currently stand, XML is used for two reasons:
* It's easy to use an XML parser to read the kind of hierarchical data
inside a descriptor.
* It's easy to generate HiveDoc directly from the XML.
= Proposed Solution =
WE can define our own special purpose langage for the descriptors. The
language could be more readable and succinct than the equivalent XML. More work
would have to be put
into the HiveDoc, to generate the HiveDoc directly from the descriptor objects,
or to generate an intermediate XML format from the descriptor objects.
Here's some examples along the lines of thinking:
{{{
module myapp.ui.toolbar, version 1.0.1
configuration-point ToolbarActions
{
element item
{
required attribute label;
required attribute icon;
attribute action-class;
attribute service-id;
conversion (class=myapp.ui.toolbar.ToolbarAction)
{
map (attribute=action-class property=action translator=object)
map (attribute=service-id property=action translator=service)
}
}
}
contribution ToolbarAction
{
item(label=Open icon=Open.gif service-id=OpenService)
}
service-point OpenService interface=myapp.ui.toolbar.ToolbarAction
{
invoke hivemind.BuilderFactory
{
construct(class=myapp.ui.toolbar.impl.OpenActionImpl log-property=log
messages-property=messages)
{
set(name=frob value=grognard)
set-service(name=dialogViewer service-id=myapp.ui.DialogViewer)
set-configuration(name=pipeline
configuration-id=myapp.ui.FileOpenPipeline)
}
}
add-interceptor service-id=hivemind.LoggingFactory;
}
}}}
This is pretty obviouslly darn isomorphic to the existing XML format. Remember,
XML started as a document format, where using punctuation for blocking
delimiters
was a bad idea, since such characters could show up in the document text. Our
use of !HiveMind deployment descriptors is a much more constrained environment,
more like scripting
than like pure documents. For example, quoting of attributes is not necessary
for most attributes, just the ones with whitespace (or other characters outside
a specific subset).
Also, many parts of XML were intended to make it easier to write an XML parser
(though, over time, things have twisted such that a fully conformant XML
parser is now an enourmous beast). Again ... not our concern.
This solution involves nailing down precisely (in BNF) what our format will
look like and writing that parser. Most likely, something like ["JavaCC"] can
be leveraged (depending on licensing). Possibly, we write a simply parser that
converts the above to a DOM-like format and work from there.
= Discussion =
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