Lesson 5: Attributes, Variables and Action Logic

Definitions

Attributes

Attributes are placeholders associated with an individual entity. Its value cannot be seen or changed by any other entity. An attribute describes an entity such as name, size, color, type, condition, etc. They can be either numeric values or character descriptors (single-word descriptions). Attributes follow an entity as it moves through a model and can’t be changed globally by events that occur elsewhere in the model. All entities have 5 system-defined attributes, including Name, Cost, ID, VATime, and CycleStart. You may also create user-defined attributes. Attributes are often used to record time, control action logic, or make routing decisions in the model. User-defined attributes are not displayed in the output reports. You should begin all attribute names with “a_”. For example, a_Type, a_Color, a_Weight. That way, attribute names are easily recognized when reading your action logic. See What is an Attribute?

Variables

Variables are placeholders for either numeric values or character descriptors (single word descriptions). They may be used to describe or track activities and states in the system, such as the number of entities that have completed a particular activity, day of the week, an hour of the day, etc. Variables are global in nature. That means any entity can view them or assign a value in the Action tab of the Properties dialog at any location. Variables are shown in the output reports and may be used to export modeling results to Excel. You should begin all user-defined variable names with “v_”. For example, v_Count, v_Completed, v_BatchSize. That way, variable names are easily recognized when reading action logic. See What is a Variable?

Action logic

ProcessModel allows you to design custom behavior in your model by writing simple but powerful logic statements. Action logic allows you to go beyond the normal property fields to determine how an entity is processed. Examples include assigning values to attributes or variables or performing a test using an If…Then statement. See What is Action Logic?

Creating Attributes and Variables

You create an attribute by clicking the Insert menu and selecting Attributes & Variables. Then click New and enter the attribute name.