Variability allows elements in one content package to influence
or modify elements in other content packages without actually directly modifying
the original content. Variability enables changes to the content while keeping
the changes separate and optional.
Variability allows you to factor your method content and processes in interrelated
units and to architect method content and processes in layers that extend
each other with new capabilities. Variability also allows you to extend and
tailor method content and processes you do not own and cannot directly modify,
and to easily upgrade to newer versions by simply reapplying your personal
changes to the upgrades.
The use of variability affects two characteristics of a method element:
its attributes and its relationships with other content elements. If an element
allows variability, the specification is shown at the bottom of the element's
description view.
For the purposes of variability, there are three groups of information
for any element to be considered:
- Attributes - pieces of data about an element such as Main Description.
- Incoming Associations - associations to other elements where the
association reference is held in the other element. In other words, the other
element has references to the subject element.
- Outgoing Associations - associations to other elements where the
association reference is held in the subject element. In other words, the
subject element has references to the other element.
In addition, associations can be one-to-one or one-to-many. See
Variability Associations for
a full list of the associations for each type of element.
Variability Type
Variability
type defines the nature of how one element affects another element using variability.
The variability types are:
- Not Applicable - The element is a base element and does not affect
another element through variability. This is the default value of an element's
variability type.
- Contributes -
A contributing element adds to the base element. Contributes provides a way
for elements to contribute their properties into their base element without
directly changing any of its existing properties, such as in an additive fashion.
The effect, after contribution, is that the base element is logically replaced
with an element that combines the attributes and associations of the contributing
element with the base element.
- Replaces -
A replacing element replaces parts of the base element. Replaces provides
a way for an element to replace a base element without directly changing any
of the base element's existing properties. This is, in most cases, used for
method plug-ins that aim to replace specific content elements such as roles,
tasks, or activities with either a completely new variant or to change the
fundamental relationships of these elements. The effect of this, is that the
base content element is logically replaced with the new replacing element
to which all incoming associations still point as before, but which has potentially
new attribute values and outgoing association properties.
- Extends -
An extending element inherits characteristics of the base element. Extension
allows Method Plug-ins to easily reuse elements from a base plug-in by providing
a kind of inheritance for the extending element. Attribute values and association
instances are inherited from the "based-on" element to the extending element.
The result is that the extending element has the same properties as the "based-on"
element, but might define its own additions. Extends is not used to modify
content of the base plug-in, but to provide the ability for the extending
plug-in to define its own content which is a variant of content already defined.
For example, a special version of a generic Review Record for a specific type
of review. The effect of this is that the base element and any number of extending
elements can be used side by side, but refer to each other through the extends
relationship. Extends also provides the key mechanism for binding capability
patterns to processes: A pattern is applied by defining an extends relationship
from an activity of the applying processes to the capability pattern. The
activity inherits association instances from the pattern and the pattern appears
to be part of the resulting process after interpretation.