UML syntax: Value specification

[ronaldtse]

Value specification

• Def.- A value specification indicates one or several values in a model.
• Semantics.- Examples for value specifications include simple, mathematical expressions, such as 4+2, and expressions with values from the object model, Integer::MAX_INT-1

Value specification-semantics

• In addition, there are language-dependent expressions defined by a language statement and the pertaining expression in that language (opaque expression), such OCL or Java expression (the language statement can be omitted if the language is implicity defined by the expression or context).

Proposal:

instance :Expression {
  symbol="+"
  operand op1
  operand op2
}

instance op1:LiteralInteger {
  value = 1
}

instance op2:LiteralInteger {
  value = 1
}

// Or explicit association
:Expression <>-> |operand| op1:LiteralInteger
:Expression <>-> |operand| op2:LiteralInteger

[w00lf]

I think we should stick with object association declaration, so the first version looks better, but because we already have short hand notation for fields I think we should introduce keyword for values, something like this:

instance :Expression {
  value symbol="+"
  operand op1
  operand op2
}

instance op1:LiteralInteger {
  value value = 1
}

instance op2:LiteralInteger {
  value value = 1
}

value value = 1 looks kind of clumsy here I guess but it will be easier to implement and I guess we don't always have value = 1 as values.

[ronaldtse]

@w00lf in this case do we want to accept both "explicit" vs "implicit" syntax?

i.e. these two blocks are equivalent:

instance :Expression {
  myvalue=1
}

// is same as
instance :Expression {
  value myvalue=1
}

We can distinguish the case of value because value = 1 is of the pattern {attribute name} {equal sign} {attribute value}.

[w00lf]

@w00lf in this case do we want to accept both "explicit" vs "implicit" syntax?

i.e. these two blocks are equivalent:

instance :Expression {
  myvalue=1
}

// is same as
instance :Expression {
  value myvalue=1
}

We can distinguish the case of value because value = 1 is of the pattern {attribute name} {equal sign} {attribute value}.

in that case, we can just use the implicit syntax as you described above.

[ronaldtse]

in that case, we can just use the implicit syntax as you described above.

OK, so we now have established the syntax pattern of an attribute with value:

class {Class name, if any} {as ref name, optional} {
  {attribute name} = {attribute value}
  {attribute name}:{attribute class} = {attribute value}
}

instance :{Class name, if any} {as ref name, optional} {
  {attribute name} = {attribute value}
  {attribute name}:{attribute class} = {attribute value}
}