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- From: "Mark L. Fussell" <email@example.com>
- To: firstname.lastname@example.org
- Date: Mon, 1 Dec 1997 06:20:09 -0800 (PST)
The MONDO Approach to: Extending Model Functionality
How can we extend the functionality of our information and information
model without becoming language specific?
Although information can be interpreted and implemented in many ways,
frequently we will want to provide possible implementations so
applications can automatically extend their capabilities in interesting
If we put the implementation into the information we will make the
information less general. If we provide no implementation (when we have
one) we make the information less knowledgeable and capable than we could
Describe implementation details in the same knowledge form as all our
other information and loosely associate/link Classes to Types through
We can represent a Java class as (the MONDO recipe in OML):
name = "COM.chimu.kernel.basicTypes.Period"
version = "v0.1"
vmRequired = "1.1"
description = "This is a simple Period which uses java.util.Dates as
its start and end values"
bytecodes = <Binary encoding=hex [[cafebabe...2000a]]>
This is readable to both Java and non-Java systems. A non-Java system
may not understand the bytecodes, but it can understand everything else
and work with the information usefully.
Next we can associate this class with a particular Type in our model.
type = <TypeReference name="Period">
language = "Java"
class = <ClassReference name= "COM.chimu.kernel.primitives.Period">
The loose association is (relatively) complete, and a particular program
can decide whether it can use and wants to use a Java implementation of
the Type Period. It can also check whether the VM level is acceptable.
We can similarly provide a Smalltalk or ".dll" implementation (assuming
we can move the ".dll" around).
None of this had any effect on our original instance and model:
start = <Date iso="1997-10-01">
end = <Date>
name = "Period"
description = "A range of dates"
properties = (
<Property name="start" type=<TypeReference name="Date"> >
<Property name="end" type=<TypeReference name="Date"> >
constructors = (
<Constructor ("start" "end")>
So they still describe "pure" general knowledge and we can still use them
independently of all the language-localized implementations.
Generally, it is a win-win situation. Implementation can be reasoned
about and chosen without directly coupling it into the information
itself. The architecture itself is also no more complicated, but only
has new objects and classes to represent implementation information. A
negative might be the added complexity of the:
associations, but the complexity can be selected as needed. Another
negative might be the required based functionality of an ObjectBuilder,
but generally ObjectBuilders must be able to simply model (e.g. as an
object with properties) anything they can not understand in more detail.
The MONDO Design addition on "Modeling and Implementing, Objects and
i ChiMu Corporation Architectures for Information
h M email@example.com Object-Oriented Information Systems
C u www.chimu.com Architecture, Frameworks, and Mentoring
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