Step 1.1 Identifying Objects

Rules for Identifying Objects

Objects ...
	Are actors. Objects can be viewed as actors that play a role in the system to be built. For example some of the actors on the stage of the purchasing system are the vendor, the purchaser, the purchase order and the purchase requisition.
	Are nouns. Objects often appear as nouns in problem descriptions. Example: "A purchase order cannot be created until a purchase requisition is received."
	Have Uniqueness. Objects can be uniquely defined. That is instances of one object can be differentiated from another. For example, a person can be male or female. By contrast money has no distinguishing attributes. It only takes on importance as an attribute of some object; for example a bank account.
	Have attributes. Objects can be described by one or more attributes. To be distinguishable from one another, objects must have attributes. For example, one automobile is distinguished from another by model, make, colour etc.
	Are data stores. Objects are the data stores in a data flow diagram.

An object can be:

	A tangible thing something you can touch Example: plane, car, truck, purchase order, person, book, invoice, target
	A role the purpose or assignment of a person, item of equipment or organisation Example: operator, customer, pilot, vendor, purchaser, scheduler
	An incident something that happens Example: delivery, attack, landing, telephone call, accident
	An interaction objects that result from associations between other objects Example: A purchase results from the association of a vendor and a customer.
	A specification a representation of rules, standards or criteria Example: recipe, articles of association, quality criteria