In the context of Domain Driven Design, is a StackOverflow tag (ie. ddd ) a value object or entity?
EDIT:
Imagine, that you have to build SO website. How would you consider 'tag'?
+6
A:
To expand a little on awhite's answer a tag is a value type Why? Because it doesn't make sense to have
var tag1 = new Tag("DDD");
var tag2 = new Tag("DDD");
Assert.AreNotEqual(tag1, tag2);
clearly they should be equal to each other because a tag has no identity except for its label. Questions and answers on the other hand are definitely entities
George Mauer
2009-03-24 20:12:21
Thank you. I couldn't have said it better myself.
awhite
2009-03-24 20:20:12
Isn't tag label his identity itself?
Bartek Szabat
2009-03-24 20:38:02
Its not that value types don't have an identity its that all instances of a particular sort have the same identity
George Mauer
2009-03-24 20:48:37
You have to render user's tag list on user page. Doesn't it make 'tag' an entity? I'm noob to DDD, can you explain more ? :)
Bartek Szabat
2009-03-24 21:30:04
George Mauer
2009-03-25 01:01:28
+1
A:
Just some additional considerations: Tags can be normalized, "DDD" should be equal to "ddd" and "DdD", and in most tag systems, spaces get replaced with "_" underscores. Also I guess the creator will be tracked for the badge system.
kitsune
2009-03-24 20:19:45
Those are certainly worthwhile considerations. Let me point out that a value type (tag) can reference an entity (user)
George Mauer
2009-03-24 20:35:47