Objects encompass both tangible as well as non-tangible concepts. Some examples which are considered to be non-tangible include electronic transactions, newspaper articles, or phone calls. There will be times when it is necessary to speak of a specific instance within your system model.
For instance, the bank may be comprised of a number of important system accounts. You may wish to describe employees, as well as executive officers. At the same time, the collection of classes will generally be described.
The term "class" is used to describe a group of objects which are related to each other, a "family" if you will. The class should not be associated with a collection of objects, because at any point you may consider the group of instances which are related to the class.
The class may be viewed as the thing which all the objects have in common. The class must not be connected with a group of objects, even though at any point you may see the group of instances which belong with the class. The class may be viewed as the thing which all the sets have in common.
From a technical viewpoint, the class is defined as the intensions for a specific set of entities, while the group of objects may conform for a characterization for a specific period of time. This period of time is referred to as being the extension.
In the notation, the rectangle will generally encapsulate the name for the class. The object must be defined as the instance for a minimum of one class. Some methods allow the object to be altered, and this class will be the instance.
The freedom that is given will enhance the power for expression for the analysis method. At the same time, because many object oriented software languages do not offer support for this function, and because the results of the modification may be showcased in other ways, many experts do not use this practice.
Specific objects could be characterized based on the indication for which the class they are in. There are times where the instance characterization may not be enough. At this point, you will not have the means to make a distinction between the many instances that make up the class.
Generally, you should wish to avoid the usage of names that describe specific objects, and the reason for this is because the objects often do not use natural names. For instance, a bank transaction or phone call does not have natural names.
Characterization for Instances
Descriptions must be used for the purpose of denoting entities which are unique. The attributes for the objects can do a job which is highly descriptive.
Another thing which must be considered is the attributes. Many entities which exist in the real world will be described by words that are responsible for indicating a number of features which are stable.
For example, most physical objects have a specific color, weight, and shape. Humans have features associated with them such as their data of birth, their eye color, and their name. A feature may be thought of as the binary relationship which exists among the class and a specific domain.
For instance, eye color may be viewed as the binary relationship that exists among the eyes, as well as a domain. The domain may come in the form of a class, and could be a parent, spouse, or an account.
There are a number of features which are applicable, but they could also become altered over time. For instance, in the natural world, both butterflies and frogs go through a number of major changes over the course of their lives.
It is necessary to avoid a great deal of flexibility, and these means that the class must be defined by the set of features which define it, which are better known as attributes. This group of features will not change. At the same time, there are a number of tricks you can use to bypass these limitations.
The notion of a relation which is binary must be considered. You must recognize the differences between the binary relationships and the contingent relationships. Binary relationships represent properties which are intrinsic, while contingent relationships showcase connections among objects which are incidental.