UML Weekend Crash Course™ - To Parent Directory

98
Saturday Morning
In a modeling tool, an attribute definition may appear as a set of fields on a specification
window, or the single line format, or a combination of the two. Regardless of the tool
interface, this set of fields can be a good tool for remembering the types of questions you
need to answer for each piece of information in your model. This data forms the foundation
for your databases, your user interfaces, reporting, and nearly every aspect of your design.
Thoroughness here pays big dividends later.
Modeling an Operation
Objects have behaviors, things they can do and things that can be done to them. These
behaviors are modeled as operations. By way of clarification, the UML distinguishes between
operation and method, whereas many people use them interchangeably. In the UML, an
operation is the declaration of the signature or interface, the minimum information
required to invoke the behavior on an object. A method is the implementation of an operation
and must conform to the signature of the operation that it implements.
Elements of an operation specification
Operations require a name, arguments, and sometimes a return. Arguments, or input parameters,
are simply attributes, so they are specified using the attribute notation (name, data
type, constraints, and default), although it is very common to use the abbreviated form of
name and data type only.
Note that if you use constraints on an argument, you are constraining the input value,
not the value of the attribute as it resides in the source object. The value in the source
object was constrained in the attribute definition within the class.
The return is an attribute data type. You can specify the visibility of the operation:
private (-) limits access to objects of the same class, public (+) allows access by any object,
protected (#) limits access to objects of subclasses within the inheritance hierarchy (and
sometimes the same package), and package (~) limits access to objects within the same
package. Given these requirements, the following notation is used to define an operation:
visibility operationName ( argname : data type {constraints}, ...) :
return data type {constraints}
Once again, writing this down as a kind of cheat sheet isn’t a bad idea. It will help you
remember all the issues you need to address when defining operations. Here’s the run-down
on each element in this expression.
Operation name: Required. Does not have to be unique, but the combination of
name and parameters does need to be unique within a class.
Arguments/parameters: Any number of arguments is allowed. Each argument
requires an identifier and a data type. Constraints may be used to define the valid
set of values that may be passed in the argument. But constraints are not supported
in many tools and will not be reflected in the code for the operation, at least not at
this point.