re: Clarifying the definition of a component

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Avraham Makeler

Nov 8, 2020, 9:35:24 PM11/8/20
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re: Clarifying the definition of a component 
The OMG UML Spec v2.5.1, section 11.6  writes: "... it specifies a Component as a modular unit with well-defined Interfaces that is replaceable within its environment." 

Also: "Component can always be considered an autonomous unit within a system or subsystem."

And: "A Component is a self-contained unit that encapsulates the state and behavior of a number of Classifiers."

And similar.  I.e., Components have well defined interfaces.

But pretty much all SW units should be like that. And abs all HW units are like that. What is special about the definition? 

So please give an example of what is not a component. Maybe a SW "item" that accesses global variables is not a component. Is that it? That's all?

So what about MS Word? Doesn't Word acess some Windows global variables? So does that mean Word is not a component?  


Eran Peleg

Nov 10, 2020, 2:55:35 AM11/10/20

Hi Avi

The source of understanding “Business Components” paradigm is the Herum and Sims book – “Business Component Factory”, 2000.

Shortly - A component may be fully autonomous, if all its services are internal, including its UI, database (resources), interfaces, internal services, etc.  However, most components have “Required” services provided by other Components.  For that concept, UML has its “Provided” and “Required” interfaces.  In theory, a system element is a Component if it has an interface (1..n interfaces).

Specifically, Word is a component, because it as UI, interface (API), etc.  Some internal data of Word, such as customization parameters, are internal, and for others Word is using another component – Windows File System to store user objects – Word documents.

The only way to use Word is through its interfaces – API, and UI.

The only way to use files is through Windows File System – API, and UI.


Therefore, both are Autonomous SW components.






Eran Peleg, CEO

Metaphor Vision Ltd.



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