what is the difference between Condition & Const

[dangel]

in sequence diagram, if I have a relation between two objects, I know that I can add constraint on the relation , but what is the difference between Constraint and Condition,, please see the image bellow:



Thank you

[qwerty]

Some glossary in OMG's papers would have helped here. According to Superstructures:

A constraint is a condition or restriction expressed in natural language text or in a machine readable language for the purpose of declaring some of the semantics of an element.

I guess something like "the sun rises every morning" or "it's dark at night". Wishy washy.

Now what is a condition? I could not find anything at the first glance. Maybe one of the Sparxians can chip in and comment.


q.

[RoyC]

In the Help:

Condition: Type any conditions that must be true in order for the Message to be sent.

Constraint: Type any constraints that might exist on when the Message is sent.

The distinction is not obvious, but my interpretation is that the Condition must exist (is True) before the message can be sent and, if False, the Message can never be sent, whilst the Constraint modifies how or when the Message is sent (for example, defines a delay in sending). But I am open to correction.

[qwerty]

Let's ask Webster's:

constraint |k[ch601]n[ch712]str[ch257]nt|
noun

• a limitation or restriction: the availability of water is the main constraint on food production | time constraints make it impossible to do everything.
• stiffness of manner and inhibition in relations between people: they would be able to talk without constraint.

condition |k[ch601]n[ch712]diSH[ch601]n|
noun

• the state of something, especially with regard to its appearance, quality, or working order: the wiring is in good condition | [ in sing. ] : the bridge is in an extremely dangerous condition.

• a person's or animal's state of health or physical fitness: he is in fairly good condition considering what he has has been through | [ in sing. ] : she was in a serious condition.
• an illness or other medical problem: a heart condition.
• [ in sing. ] a particular state of existence: a condition of misery.
• archaic social position or rank: those of humbler condition.

• (conditions) the circumstances affecting the way in which people live or work, especially with regard to their safety or well-being: harsh working and living conditions.

• the factors or prevailing situation influencing the performance or the outcome of a process: present market conditions.
• the prevailing state of the weather, ground, sea, or atmosphere at a particular time, especially as it affects a sporting event: the appalling conditions determined the style of play.

• a state of affairs that must exist or be brought about before something else is possible or permitted: for a member to borrow money, three conditions have to be met | all personnel should comply with this policy as a condition of employment | I'll accept your offer on one condition.