Re: [UML Forum] What does the arrow end of a dependency relationship indicate?

[H. S. Lahman]

Responding to Martin...

Hello,
i'm preparing for the OCUP fundamental test and have found some sample questions with answers.
one is regarding dependency relationship: What does the arrow end of a dependency relationship indicate?
with possible answers:
A. more general classifier
B. element initiates communication
C. whole in a whole-part relationship
D. client element is affected by a change in the supplier element
E. supplier element is unaffected by a change in the client element
correct answer is E.

why is also D not a correct answer?

Because this borders on being a trick question. Dependencies are about what one element knows about the other element. A basic tenet of dependency management is that dependencies should be one-way with the client knowing something about the supplier but the supplier knowing nothing about the client.

Superficially it seems that both D and E are the correct answers. The trick is that "knowing" does not necessarily imply anything about change. Thus, in practice D is usually true, but not always. OTOH, E is always true because the supplier knows nothing about the client.

They are also employing a limited definition of 'change'. They are talking about changes to the semantics of the element (as opposed to changes in the <attribute> state of the element). Thus the dependency may be that the client knows the supplier has certain knowledge and uses that knowledge, without any change in semantics.

-- 
Life is the only flaw in an otherwise perfect nonexistence
   -- Schopenhauer

Imagine how much more difficult physics would be if electrons had feelings
   -- Richard Feynman

Rene Descartes went into a bar. The bartender asked if he would like a drink. Descartes said, "I think not," and disappeared.

H. S. Lahman
H.la...@verizon.net
software blog: http://pathfinderpeople.blogs.com/hslahman/index.html
software book: Model Based Development, Addison-Wesley, 2011
geology book: The Evolution and Utilization of Marine Resources, MIT Press, 1972

[david reye]

Martin,

I understand your confusion.

The answer to the question is that the arrow end of a dependency relationship represents the supplier and the tail represents the client.

The provided answers are poorly worded. A, B, C are clearly wrong.

I think D is trying to say [the arrow end indicates ] the client element, which is affected by a change in the supplier element

and E is trying to say [the arrow end indicates ] the supplier element, which is unaffected by a change in the client element

By that interpretation, D is wrong and E is right.

Without the "which", the answers do not address the question - they simply describe a dependency relationship, not what the arrow represents.

Cheers,

David

On 23/05/2013, at 6:15 PM, Martin wrote:

Hello,
i'm preparing for the OCUP fundamental test and have found some sample questions with answers.
one is regarding dependency relationship: What does the arrow end of a dependency relationship indicate?
with possible answers:
A. more general classifier
B. element initiates communication
C. whole in a whole-part relationship
D. client element is affected by a change in the supplier element
E. supplier element is unaffected by a change in the client element
correct answer is E.

why is also D not a correct answer?

using dependency relationship means telling which side of element is dependant, not independant (E must not be correct if there also exists a reverse dependency between same classes  - is that allowed?:).

definition of dependency: "A dependency is a relationship that signifies that a single or a set of model elements requires other model elements for
their specification or implementation. This means that the complete semantics of the depending elements is either
semantically or structurally dependent on the definition of the supplier element(s)."

thans for help,
Martin

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David Reye

Software Systems Consultant

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